Download user presentations that focus on applications of FLOW-3D for the water & environmental industry from past users conferences.
Study of the outlet structures of the Marne Reservoir
Gwenaël Chevallet and Eric Vuillermet, BRLi
The Marne reservoir (350 Mm³, 48 km²) is the largest artificial lake in France and one of the largest in Europe. Its main purpose is to protect the city of Paris against the floods of the Seine river. The embankment dam is characterized by a height of about 20 m. The flows are restored downstream using (from upstream to downstream): an intake tower controlled by two tainter gates, 2 galleries, a dissipation basin, a stilling basin, and a channel. Seine-Grands-Lacs, which manages the reservoir, wanted to study the flow conditions in the dam’s release structure in order to evaluate the maximum flow rates that can be discharged before the galleries are loaded, and redefine the structure’s “Z-Q” law of the discharge outlet controlled by the 2 tainter gates. The FLOW-3D model was subjected to a very fine calibration. To calibrate the flow, an ADCP was used. To calibrate altitude, GPS was used, and laser surveys were taken of the water line for different flow conditions. In addition, many sensitivity tests were carried out on different parameters (roughness, air entrainment, etc.). The results of these calibrations were excellent and the maximum flow before loading the galleries was estimated at about 245 m³/s.
The Vlachovice Dam – pre-project preparation
Tomas Studnicka and Jan Sehnal, AQUATIS a.s.
In hydrological terms, the Czech Republic can be called “the roof of Europe,” as it is situated in the watershed of three seas. Practically all its major watercourses drain water into neighbouring countries. The water sources of the Czech Republic are thus almost exclusively dependent on precipitation. As drought in the Czech Republic has become more common in recent years, the government has passed a resolution to build four new dams with water reservoirs in order to help with the security of the water supply during periods of drought. The largest one will be the Vlachovice reservoir on the Vlara River in the Zlín Region. At present, the Vlachovice Dam project is getting more concrete contours because the government has included it in its priorities. As part of the pre-project preparation, FLOW-3D v11.2 has been used to assess and optimize various hydraulic structures of the Vlachovice Dam, especially the spillway, chute and stilling basin. Both RNG and LES turbulence models have been utilized in the simulations, as well as the air entrainment model. The presentation will discuss the obtained simulation results and the impact of the turbulence model on predicted flow characteristics.
Storm surge barrier, Nieuwpoort, Belgium
Jeroen Adema, Arcadis Netherlands
The new storm surge barrier in Nieuwpoort is part of the Coastal Safety Masterplan that was approved by the Flemish government in 2011. The storm surge barrier protects one of the largest recreational harbors in northern Europe and its hinterland. In a feasibility study, a rising sector gate barrier turned out to be most suitable for Nieuwpoort. The reduction of the width of the access channel causes the flow velocities to increase. Additional studies were carried out to optimize the nautical conditions to navigate through the opening of the barrier. Including culverts in the abutments on both sides will reduce longitudinal velocities. In FLOW-3D, the access channel to the harbor has been schematized and different guide wall designs have been implemented to optimize the cross currents. Quasi-steady state simulations were carried out for spring and average tidal conditions. A comparison of the flow patterns has shown that an optimal design of the guide walls can reduce cross currents significantly.
Numerical modeling of air entrainment in an aeration chamber and pipes
Pin-Tzu Su, ATE Energy International
This is a study of warm water discharged from an aeration chamber and pipes into the ocean. In the discharging process, air can be entrained into the pipes. When air flows through the pipes, the pipe stability is reduced. Hence, to study the water which is entrained with air in the aeration chamber and pipes is important for the power plant design, and an applicable structure design which can decrease air entrainment is important for practice work. Due to air density being less than sea water, the air gathers at the top of the pipes. Air vents are designed at the top of the pipes to allow air to escape into the atmosphere. This numerical simulation analysis compares different designs which influence the amount of air entrainment during discharging. The interaction between the fluid and the air diffusion is also investigated, so the appropriate designs can be determined.
Generating performance curves for sharp crested gates on the Zambezi
Gillian Murphy and John Chesterton, Mott MacDonald
A hydropower scheme is being developed in Africa, located at a wide waterfall which provides a natural head difference. However, during high flows the falls are almost completely drowned. During feasibility studies, a series of pneumatically controlled steel flap gates were proposed to provide control across the river as a robust solution that would accommodate flood flows and debris with minimal mechanical equipment in-stream. While some literature exists on the capacity of these gates, model testing has been limited to situations that did not represent the proposed location. In addition to this, the drowning of the falls at high flows required submergence curves. A full range of discharge coefficients were needed for a range of gate openings and submergence conditions. Given the length of the gates, in some cases over 120m, FLOW-3D was used to develop a range of vertical 2D models. A number of geometries were run concurrently within the same model to reduce the number of model files and ease post-processing. A total of 42 scenarios were run in 7 models. As sharp crested weirs require ventilation conditions to be accurately represented, this initially presented a challenge to the modelers. To overcome this, a combination of void pointers and timed void droplets were used to successfully represent vented conditions without forcing.
Flow velocities within Pont des Chèvres transfer work: Comparison between FLOW-3D model and site measurements
Anaïs Faivre, Thomas Pretet, and Julien Vermeulen, EDF-CIH
The Pont des Chèvres works are located in the French Alps. These works are composed of two basins which are closed by the Pont-des-Chèvres dam and connected through a transfer work. On the right bank, the “Arc basin” collects the flow from the river Arc. On the left bank, the “power station basin” collects the turbined water from the Orelle power plant and contains the Saussaz II intake. The “power station basin” also corresponds to the Super Bissorte pumped storage scheme lower reservoir. To prevent floating materials from the river Arc entering the power station basin, EDF wanted to set up a boom on the Arc basin side of the transfer work (this device is a screen floating over the free surface). In order to design the boom, it was necessary to estimate the flow conditions close to the boom for several operating conditions. Therefore, 45 FLOW-3D simulations were run to determine the flow rates and surface velocities within the transfer work for different water elevations within the two basins. One month later, EDF made some site measurements. The surface velocities were measured by LSPIV method. The comparison between numerical results and site measurements shows that the velocities are similar. The numerical model is conservative: it overestimates the velocities by 10%.
Using FLOW-3D to evaluate mixing performance and hydraulic efficiency in a contact basin
Steve Saunders, Ibis Group
In both potable and wastewater treatment facilities, process tanks wherein multiple constituents get mixed together are common. In the past, their designers have relied on 1D process models that have been continuously refined over years of practice. These process models often assume perfect hydraulic efficiency or “plug flow” and thorough mixing of constituents. In reality, hydraulic efficiency can be compromised by short circuiting or dead zones. Also, the water may pass through a system without complete mixing, thus resulting in zones of excessive or insufficient process constituents. In compensating for this, a facility can wind up being overdesigned and running at sub-optimal efficiency. One obvious course of action is to invest in 3D modeling during design and retrofit stages. Physical simulation of process tanks is expensive, due to the nature of tracer dispersal and the subsequent requirements for the models to be made at large scale ratios. Consequently, CFD simulation has come to the fore as a practical and cost-effective means of evaluating process tanks. Through the introduction of tracers into a CFD model, both hydraulic efficiency and mixing efficacy can be readily evaluated and documented. Also, by applying reacting properties to tracers, it is possible to simulate the decay of a disinfectant plus its ability to neutralize microorganisms. This presentation will show the setup and execution of a FLOW-3D model in the evaluation of a contact tank, where a tracer representing an active disinfectant is introduced near the model inlet and tracked as it progresses to the model exit.
Fish pass on the Revúca River
Jakub Kedrovič, Miloš Kedrovič, and Magdaléna Vicianová, Vodotika, a.s.
In Slovakia there is currently a great effort to remove existing barriers in water courses that prevent aquatic animals from migrating downstream or upstream. The barrier in this case is a fixed weir crest which creates a level difference of approximately 4.0 m on the Revúca River. This construction impedes the longitudinal movement of fish and other animals living in a given location upstream or downstream. As a solution, our company proposed a transition from a fixed to a controlled weir, which allowed the placement of a new slot fish pass between the weir and a small hydropower station. The final parameters of the fish pass resulted from a mathematical model computed in FLOW-3D. The parameters of the first design were based on methodical regulation and instructions from biologists. Unsurprisingly, the results of the first simulation were not acceptable, so the geometry of individual pools was changed. A terraced bed was proposed which would elevate the top of the slots so that they would not overflow, while leaving the width of the slots unchanged (400 mm). The size of the pools was then decreased to divert and slow down the stream line. The result of optimization was the discovery that for this kind of fish pass, it was best to reduce the width and length of the pools. The modelling process also provided us with the information that overflowed slots are inappropriate, as they cause aeration of the flow. To summarize, thanks to the application of modern computation techniques we were able to propose the best parameters for a fish pass that will ensure the correct flow for aquatic migration.
Reconstructing da Vinci’s Dam Valley
Emanuele Andalo and Roberto Saponelli, Protesa S.p.A.
Stefano Mascetti, XC Engineering S.r.l.
On the occasion of the 500th anniversary of Leonardo da Vinci’s death, it was decided that Protesa numerical services would do an historical investigation of one of Da Vinci’s studies: the design of a dam in a valley near his origin village, Vinci. This dam was designed for the purpose of generating a water basin for the population and to operate hydraulic machines designed by Leonardo himself. The project was never realized, and questions arised about the feasibility and impact of this project. For this study, environmental scanning techniques were used to make a 3D mapping of the valley in which Leonardo had intended to locate the dam. This scan provides the base of the FLOW-3D model, to which a dam was added, the design of which was created based on the dam built near Grosseto (which collapsed around 1500). Finally, the water basin was created, filling the valley as Leonardo had planned. The purpose of this activity was to combine top-level environmental scanner technologies with CFD simulations to reproduce in a virtual environment the Renaissance-era dam working conditions, adding the value of a dam break analysis to evaluate the consequences in the affected areas.
Physical and numerical modelling of flow at tunnel spillway intake
Vincent Gizard, EDF-CIH
This presentation deals with the modelling of the Gage Dam tunnel spillway intake provided by a flap gate and a piano key weir. The aim of the study was to compare FLOW-3D numerical results with physical scale model results, in terms of discharge, submergence, freeboard, etc. Numerical modelling is performed within one global mesh block with four nested mesh blocks (mesh sizes: 0.40, 0.20, 0.10 m). Despite complex geometries, the discharge results turn out to be quite similar (difference lower than 5%) in the physical and numerical models, whereas the downstream intake water levels show bigger differences as well as some contradictions, which will be reviewed.
Numerical investigation of Aşaği Kalekő spillway using FLOW-3D
Mete Köken and İsmail Aydin, Middle East Technical University
Aşağı Kaleköy Dam is designed to have an ogee spillway fitted with radial gates that is connected to a stilling basin through a chute channel. There are two aerators within the spillway chute to protect the structure from cavitation damage. A numerical and experimental study was conducted to investigate the flow within the reservoir, over the spillway and through the energy dissipation structures, both at design discharge and probable maximum flood discharge. A single phase numerical solution was used, and the air entrainment model was activated for the simulations of the spillway and the energy dissipation structure. A unit width physical model was constructed at a scale of 1/30 at the Hydromechanics Laboratory at METU to measure the capacity of the aerators. This model was used to calibrate the air entrainment model in the numerical simulations. It was observed that the air entrainment model was not able to predict the scale effects in terms of air entrainment in the model and prototype scales. Therefore, distributed air sources are added to the locations of the aerators for accurate simulation of the air-water mixture flow.
Turbidite forward modelling in FLOW-3D for geological simulations
Chiari Barbieri, Eni Upstream and Technical Services and Raul Pirovano, XC Engineering S.r.l.
The aim of this work is to present how FLOW-3D has been used in the geological field, with a focus on the simulation of underwater gravity-driven flows and their associated deposits. In order to manage and define the peculiarities of this process, a new graphical interface has been developed, giving the user the ability to modify a topographic surface and use shapefiles to define areas with different lithological compositions, working directly on georeferenced coordinate systems. Moreover, embedded with the GUI there is a customized, proprietary version of the solver (property of Eni Upstream and Technical Services), that allows for accurate simulations of bi-partite gravity-driven flows. The numerical model has been calibrated on flume experiments, with a good agreement between simulation and reality. Thanks to these developments, several tests have already been made on real cases, both for exploration, simulating the deposit due to past multiple runs, and for geohazard, to understand the possible effects of a future impact of turbidite flows on pipelines and to reduce the associated risk.
A Case Study of Flood Modelling from Tailings Storage Facility Failure
Rudolf Faber, Pöyry Energy GmbH
Tailings material is deposited in stacks which may reach heights of 100 meters. Depending on the material properties, in the case of failure such stacks pose risks of liquefied material runout, flooding, pollution, etc. Several aspects from a recent client project on tailings material flood modelling will be introduced. After a brief outline of the study area with the areas at risk around the storage facility, the failure and flooding process based on the literature are outlined first, including the non-Newtonian fluid character of the tailings material. Second, the model setup in terms of topography, fluid parameters, meshing and boundary conditions are discussed as well as sensitivity aspects. Third, the definition of failure scenarios under investigation is addressed with a focus on the tailings stack’s breach outflow as a main factor for the intensity of the simulated flooding. And finally, selected results are presented and specific experiences from the entire modelling project are discussed.
Complexity & Diversity in Sands & Gravels: A Case Study of Decision Options for Sediment Transport Modelling
Kate Bradbrook, JBA Consulting
FLOW-3D’s sediment transport model is one of the most advanced available to commercial users. For example, it is possible to specify several bed layers, each with a different grain size distribution. This presentation will start by showing a scour simulation at a case-study bridge with such a detailed representation and discusses the information needed as well as the computational overheads and shows interpretation of the results. However, in many real-world examples, the required input data for such a detailed representation will simply not be available; either significant assumptions would have to be made or a simpler approach taken. In either case, sensitivity testing is standard practice. We have therefore repeated our case-study bridge simulation with different levels of detail and assumptions. We will show, for example, the difference in modelling requirements and potential conclusions resulting from decisions such as uniform sediment versus mixed grain sizes, single layer versus several layers, and clear water input versus upstream sediment supply. As with many modelling decisions, the appropriate level of detail will be case-specific depending on specific characteristics and the reason for modelling. It is hoped that the comparisons shown in this presentation will provide useful information to help this decision-making process. The presentation will end with a real-world example where, with the minimum of data, we attempt to replicate a catastrophic scour event.
Hydrodynamic Forces on a High-head Slider Gate
Boris Huber, Vienna University of Technology
Slider gates are commonly used to operate bottom outlets in high-head power plants. When the gates are opened, flow passes underneath, generating hydrodynamic forces which can be lift or drag forces. Usually the weight of the gate is sufficient so that it closes automatically, but if lift forces are too high, the gate might not close. In the case under consideration, hydrodynamic forces on a rather unconventional gate were simulated with different CFD codes.
Influence of Floating Debris Racks on Flow Rate at Standard Spillways
Grégory Guyot, Christian Lassus, and Cécile Idelon, EDF-CIH
Flood events may entrain large amounts of floating debris; especially large wood debris may clog or dramatically decrease the spillway capacity. For safety reasons, it is crucial to find a solution that maintains the required discharge and prevents the floating debris from entering the lake upstream. Furthermore, a floating debris rack may be proposed to avoid the clogging of the spillway. Therefore, two numerical models were achieved to precisely determine the best location of a rack. For that purpose, FLOW-3D was coupled with EDF’s Python automation. It enabled around 1300 simulations to be created and run automatically in order to analyze the ranges of all influent parameters. A first simulation run was performed in 2D to efficiently determine the most suitable location. Then a full 3D model was used to investigate the influence of the rack design and the type of debris on the discharge drop. Both of the numerical results were compared with physical experimentation. First, the numerical models help us determine a location where the discharge capacity is preserved despite the debris. Second, they give us an accurate understanding of the different clogging processes depending on the wood debris type.
Orlik Dam – Protection of the Dam Against Large Floods
Tomas Studnicka and Jan Sehnal, AQUATIS
The Vltava Cascade is a sequence of 9 retention reservoirs on the Vltava River, and the Orlik reservoir forms a fundamental part of it. Holding 720 million m3 of water, it is the largest retention reservoir in the Czech Republic. In August 2002, catastrophic floods hit a considerable part of the Czech Republic. The region most affected was the Vltava River basin. During the flood event, the water level in the Orlik reservoir considerably exceeded the maximum allowable level, which resulted in the flooding of the Orlik hydropower plant that put it out of operation. The purpose of the project “Orlik Dam – Protection of the Dam Against Large Floods” was to design technical measures that would withstand extreme floods. The new standards for dam safety in the Czech Republic require that the most important water structures of this type must safely stand up to a Ten Thousand Years – Control Flood. In the project, numerical modelling followed by physical modelling have been used. This presentation describes the performed numerical simulations and compares their results with the data obtained through physical modelling.
Spillway Assessment – When is a Splash a Splash?
Mary Jeddere-Fisher, Mott MacDonald
As standards change and improvements are made in hydrological methods, existing spillways often need re-assessment. Typically, water depths and velocity measurements are required along the length of the spillway. The high level of detail in results made accessible by FLOW-3D is very desirable and can be used to provide high resolution long profiles of water depths and velocities, making it possible to refine and minimise planned spillway upgrade works. However, such measurements from unsteady simulation of turbulent flows are not straightforward. Careful consideration must be made in terms of how data are extracted, and what sampling frequency and period are sufficient for a robust assessment. This presentation will discuss some of the sampling methods used to extract such data and make a comparison of FLOW-3D results against a recent physical model study which looked at splash heights and training wall requirements on stepped spillways.
Numerical simulation of air entrainment and transport in low-Froude-number hydraulic jumpsFabián A. Bombardelli, UC Davis, Milagros N. Loguercio, National University of La Plata and Kaveh Zamani, Water Research Laboratory We assess the prediction capability of FLOW-3D to reproduce the flow and air transport in hydraulic jumps for different low Froude numbers. We compare results including different levels of complexity in the theoretical model to predict the mean flow, turbulence statistics as well as, more importantly, void fractions. To the best of our knowledge, this is the first time a validation with an extensive level of rigor has been conducted. Due to the lack of experimental works including data for the mean flow, turbulence statistics and air concentration altogether, one flow was selected to first check the accurate representation of the mean flow in a low-Froude-number hydraulic jump, and then other laboratory tests were chosen to analyze the void fractions. Rigorous mesh convergence tests were done to validate the numerical models. Results revealed that the numerical model can reproduce the flow field and turbulence statistics in very good agreement with data, whereas the void fractions are not as accurate as the above but that they are still acceptable and of the same level of agreement with published works. The presentation addresses the behavior of the different complexity levels against data.
Boundary Dam – Total dissolved gas analysis
Nikou Jalayeri, Hatch
The Boundary Dam is located on the Pend Oreille River in northeastern Washington. The project consists of a 340 ft. high concrete arch dam, seven low level sluiceway outlets, two high level overflow spillways, and a 1003 MW powerhouse. The Boundary Hydroelectric Development have been shown to produce high total dissolved gas (TDG) concentrations in the river reach downstream. Studies were commissioned to determine modifications to the project’s spillway structures to help mitigate this gas production. Resolution of many of the hydraulic design issues for the study relied heavily on the results of numerical hydraulic models. These modifications were constructed and tested in the field. The CFD model that was developed in support of these studies was used to simulate flows through a number of the project’s seven sluice gates and two overflow spillways. The model was set up to track the pressure- and time-histories of representative air bubbles within the plunge pool and tailrace. These data were then used as input to a TDG predictive tool to help predict total dissolved gas production in the tailrace. The overall predictive performance was successfully calibrated and validated to actual prototype (field) TDG data.
Making a wave in Idaho
Bruce Savage and Greg Roberts, Idaho State University
Flooding events pose a risk to nuclear reactor facilities, as evidenced by the recent Fukushima Daiichi nuclear power plant failure and other flood events. To improve probabilistic risk modeling of these circumstances, water rise, spray, and wave impact testing capabilities are being developed for the Component Flooding Evaluation Laboratory (CFEL) at Idaho State University. The goal of the wave impact testing is to develop a device that can test prototype scale components for extreme wave impacts. The assumption is that a tsunami wave represents a worst-case scenario. The goal was to develop a device that can simulate the impact of tsunami wave heights up to 20 feet. FLOW-3D was used to evaluate and explore different conceptional designs including horizontal pistons, a vertical piston, or an air pressure system as methods of fluid displacement are explored. The results indicated that an air pressure system using baffles produced a near-vertical wave section.
Two fluid modelling of a spillway flow
Stéphanie Thériault and Laurent Bilodeau, Hydro Quebec
We have been exploring the use of two-fluid modelling – air and water – for examining the flow downstream of a spillway gate. Our presentation will show how we went from one fluid to two fluids by means of a restart, plus a number of parameter and meshing adjustments. We will go over what worked well for us and how several pitfalls were circumvented.
Stratified environmental flows interacting with obstacles
Jian Zhou and Subhas K. Venayagamoorthy, Colorado State University
In this presentation, two published studies of stratified environmental flows interacting with solid obstacles using FLOW-3D will be discussed. These studies are respectively: (1) numerical simulations of intrusive gravity currents interacting with a bottom-mounted obstacle in a continuously stratified ambient; and (2) numerical simulations of the propagation dynamics of bottom-boundary gravity currents over and through a submerged array of cylindrical obstacles. In both of these studies, the numerical results from FLOW-3D were observed to be in excellent agreement with experimental data. With the aid of the robust numerical solver and the unique FAVORTM technique, the suitability and capacity of FLOW-3D to accurately model and provide fundamental insights into this important class of flows are demonstrated.
1Funded by the Office of Naval Research and the National Science Foundation
Spillway assessment with FLOW-3D
John Chesterton, Mott MacDonald
As standards change, existing spillways often need re-assessment. Complex, non-standard spillway geometries introduce unpredictable flow patterns requiring detailed modelling. FLOW-3D is well suited to these problems but, given the high consequences of dam failure, require sensitivity and validation studies to ensure sufficient accuracy. Important outputs usually include flow capacity and detailed water levels and velocities. This presentation will discuss the issues encountered while evaluating these outputs which often show considerable sensitivity to boundary conditions, grid resolution and turbulence model selection. For many of these problems, the LES turbulence model has been required and used successfully but would benefit from further development. The use of FlowSight to output the detailed information required for engineering design will also be discussed along with the limitations encountered.
Modelling oscillating flow structures: the cylinder laminar wake case study and a shallow reservoir application
Daniel Valero, FH Aachen University of Applied Sciences, University of Liège
Daniel B. Bung, FH Aachen University of Applied Sciences
Sebastien Erpicum and Benjamin Dewals, University of Liège
RANS modelling is particularly suited for the study of the mean flow in many environmental applications. It allows accurate determination of the most important three-dimensional features of common hydraulic problems. However, as numerical modelling becomes more powerful and robust, both the researchers’ and the practitioners’ communities are focusing on more complex and challenging problems. In this regard, a natural question arises: what are the real capabilities of RANS modelling for oscillating flow structures? Little is known about RANS performance in respect to fluctuating flow quantities, but it is reasonable to expect some loss of accuracy when compared to the mean flow features. In this study, a simple geometry (cylindrical pier) is subject to different numerical schemes in order to test their effect on the development of the physically based flow instabilities. Mesh refinement has shown to enhance the perturbation growth rate while maximum CFL value has not produced any effect. RNG k-ϵ and k-ω have shown to be more dissipative than k-ϵ. Some advection schemes seem to increase the spurious perturbation converging to the physically-based ones. Additionally, it has been observed that introducing an experimentally based perturbation at the inlet has proven to speed up the process. Finally, a proper orthogonal decomposition method is used to compare the RANS performance with a shallow reservoir experiment where highly unsteady structures have been investigated.
Nove Herminovy Dam – hydraulic modelling
Tomas Studnicka, Aquatis
The Opava river basin in the north-eastern part of the Czech Republic represents a region which was heavily affected by the devastating floods in 1997. By a resolution adopted in 2008, the Czech Republic government approved the final variant of measures to reduce the flood risk in the Opava river basin. The approved variant consists of a set of technical and semi-natural (nature-friendly) measures. A target level of the flood protection should be reached by the retention effect of a new dam acting in synergy with other measures. Numerical modelling using FLOW-3D was used to assess and optimize the performance of the initial spillway and bottom outlets design as well as the stilling basin of the dam so that desired capacity and functionality was achieved. Physical modelling was then used to evaluate the optimized design of the Nove Herminovy Dam. The presentation describes the performed numerical simulations and their results are compared with the data obtained by means of physical modelling.
Numerical investigation of a combined system of piano key weirs and stepped spillway
Mete Koken and Ismail Aydin, Middle East Technical University
Piano key weirs are useful overflow structures to increase discharge capacity per unit length of spillway crest for relatively small heads over the weir compared to a standard straight weir crest. Stepped spillways are an economical alternative for roller compacted concrete dams which use the dam surface as an energy dissipating structure leading to a more economical stilling basin at the toe of the spillway. Air entrainment and bulking effects are extremely important in a stepped spillway, which should be taken into account in the modelling process. Aşağı Kaleköy Dam spillway is hydraulically a very complicated spillway with different components which have different hydraulic characteristics. Because of their limited crest length, piano key weirs are used at the crest of the dam which is connected to a stepped spillway. Since the total design discharge cannot be passed through this system, six individual orifice spillways are added inside the dam body. Because of the topographic limitations the spillway is contracted in the downstream direction. All of these features required an extensive numerical investigation in the prototype scale. In this study, flow conditions for Aşağı Kaleköy Dam Spillway are investigated using FLOW-3D.
3D model of hydraulic efficiency of a grate inlet for streets
Jackson Tellez-Alvarez and Manuel Gomez, Institute FLUMEN
Beniamino Russo, Technical College of La Almunia (University of Zaragoza)
Poor surface drainage design is a common problem in our cities and often it can generate significant local urban floods. Furthermore, many studies are available to estimate the flows on the street network (runoff) as the flow in the storm drainage system (sewer flow). However, the studies show an inability to characterize the hydraulics of the elements which achieve the catchment of water: the inlets. In order to study this problem, a 3D numerical model has been developed to replicate the hydraulic performance of a common grated inlet, realised through the experimental facilities of the hydraulic laboratory of the Technical University of Catalonia. FLOW-3D predicts the performance of hydraulic behaviour of a specific grated inlet with similar results to the data obtained experimentally. The proposed method can be used to estimate the efficiency of grated inlets that were not tested in the laboratory. The advantage of this model is the use of hybrid shallow water 3D simulation, when the flow approaches 3D structures within a shallow water environment such as a grate in large domains. The turbulence model chosen was re-normalization group (RNG). The simulation was performed on a computer with Intel Core 2 Duo, 2.3 GHz and 12 GB RAM and the average time of simulation was around three days. The simulation domain was composed by 850583 cells elements that represent the platform of the grate in real scale.
CFD analysis of air-water flow structure in a circular dropshaft
Muhammed Uçar and S. Y. Kumcu, Necmettin Erbakan University
Circular dropshafts, commonly used in urban storm water systems for energy dissipation and flow control, are characterized by significant flow aeration. This study is made mainly for the aeration properties of dropshafts. The investigation is executed using both experimental and numeric modeling in the study. Experimental modeling studies have been used to achieve designing hardness, however, the studies take time and may not be economical. With the use of high performance computers and more efficient computational fluid dynamics (CFD) codes, the behavior of hydraulic structures can be investigated numerically in reasonable time and expense. In this study, FLOW-3D, which uses the VOF (Volume of Fluid) method and solves RANS (Reynolds Averaged Navier-Stokes) equations, is used for numerical modeling. In order to verify the numerical modeling results, physical experimental studies were set up in the laboratory. In the numerical model, a series of tests were performed in a circular dropshaft having two identical horizontal inflow and outflow circular channels and a circular drop chamber having diameter of various diameters to observe flow patterns and measure air bubble entrainment flow parameters. In the laboratory, a series of experiments were performed in a circular dropshaft having two identical horizontal inflow and outflow circular channels and circular drop chambers having alternated diameters for observing flow patterns and measuring air bubble entrainment flow parameters. Experimental observations showed distinct flow regimes associated with nappe impact in the shaft pool, in the outflow channel, and in the opposite shaft wall. New, detailed air-water flow measurements were conducted in a circular dropshaft using a double-tip fiber optical probe. Measurements of void fractions, bubble frequencies and bubble sizes were conducted for different flow conditions of the circular inflow channel. In the shaft pool, the results obtained from measurements demonstrated the complexity of different air entrainment mechanisms. Consequently, the distance after hydraulic jump to reach uniform flow for different discharges and gate opening ratios are obtained. And all measurements are compared with FLOW-3D in order to investigate the ability of the CFD modeling. FLOW-3D and experimental results showed a great consistency with each other.
ADP Observations of the Flow in a Tropical River and Numerical Modeling
Rubén Morales, Gabriel García, Víctor Mejía, Ernesto Aguilar and Santiago Flores, Instituto Mexicano de Tecnología del Agua
The Carrizal River is located in the southern coastal plains of the Gulf of Mexico. It is a branch of the Grijalva River that discharges into the Gulf of Mexico. In order to assess the hydraulic features of the Carrizal River and the impact of the flow over a group of pile bridge structures, systematic ADP measurements were carried out along 1.5 km of the river during May and June 2016. Therefore, data was gathered during four field experiments measuring the water level gradient, river bathymetry, discharge across several sections and the spatial flow velocity field upstream and downstream the bridge. Analysis of the data depicts the main hydraulic features of the study area and gives a clear understanding of the dynamics of the flow along the river and through the pile bridge structures. The data was synthesized using the FLOW-3D and the model was set up to simulate 3 different scenarios such as those observed during the field experiments. The simulations show similar patterns of the river hydrodynamics and provide further insight into the dynamics of the river flow. It is quite evident how the structures play an important role in modifying the flow and, consequently, there is an impact of the flow on the morphology of the river. The field measurements, along with the FLOW-3Dsimulations, have allowed the flow dynamics of the river to be better understood so that actions can be taken to ameliorate the erosion on the river banks. The numerical results are preliminary but along with the field data are the basis to extend the analysis and establish in detail the impact of the flow on the pile bridge structure and the morphology of the river.
Application of FLOW-3D at BC Hydro Dams
Faizal Yusuf, BC Hydro
FLOW-3D has been used to investigate complex hydraulic issues at several existing BC Hydro dams and to assist in the design and optimization of proposed facilities. Four case studies are presented that highlight the application of FLOW-3D to existing and proposed hydraulic structures at BC Hydro. At Bennett Dam, differences in the spillway geometry between the physical hydraulic model from the 1960s and the prototype make it difficult to draw reliable conclusions on shock wave formation and chute capacity from physical model test results. CFD model simulations of Bennett Dam spillway showed that passage of the Inflow Design Flood would not result in overtopping of the spillway chute walls as long as all three radial gates are opened as prescribed in existing operating orders. FLOW-3D was also used at Strathcona Dam to investigate the effects of poor approach flow conditions and potential pier overtopping at reservoir levels above the current operating range. Significant improvements in the design of a proposed passive spillway at John Hart Dam were made through a systematic optimization process using FLOW-3D. For Site C Dam, which is currently under construction along the Peace River in BC, CFD modelling was used to complement physical hydraulic modeling for the design and refinement of the approach channel, power intakes, spillway, stilling basin, tailrace and diversion tunnels. Highlights from the use of CFD modelling in the design of Site C hydraulic structures, which include the largest spillway in terms of discharge capacity at BC Hydro, will be presented.
Estimating Forces on Non-Conventional Miter Gate
Adrian Strain, HDR, Inc.
The non-conventional use of a miter gate was proposed during the design process of a flood control project. To gain confidence in the gate design, a CFD (Computational Fluid Dynamics) study was performed. Typically, miter gates close against static water, however, for this application the proposed miter gate closed against tidally-driven flow velocities. The simulations combined the Large-Eddy Simulation (LES) turbulence model with the General Moving Objects (GMO) module. The closing motion of the gate was prescribed and key design factors affecting the operational parameters of the miter gate were identified. Data from the FLOW-3D simulations were applied to an uncoupled structural model to determine deflections and mechanical loads. Several analysis points were identified and data was extracted from the results using arbitrary surfaces and user defined variables in FlowSight.
Earthen dam failure analysis
Bernard Twaróg, Cracow University of Technology
This presentation will discuss the issues in different areas of environmental engineering: failure of earth dam – washout analysis, failure of levee in Sandomierz – impact analysis, catastrophe of the largest landfill in Europe – impact analysis, and propagation of emergency threats in the river valley Soła as a result of the failure of the artificial power plant reservoir, located on the top of the Żar mountain. The results will be presented using NMT and GIS analysis.
Performance assessment of FLOW-3D for environmental modelling
Daniel Valero and Daniel B. Bung, FH Aachen
Because of increased interest in 3D hydro-numerical modelling, new environmental problems are faced that, in some cases, still lack of validation. Some knowledge on accuracy levels for different problems might encourage practitioners to choose a RANS model to help them design to the desired level of accuracy. Some experiences with numerical modelling of common environmental flows are presented, showing the main strengths of the model and how results were analysed in order to get the most out of them. Flows such as smooth and stepped spillways, hydraulic jumps, USBR stilling basins and environmental discharges with turbulent contaminant dispersion have been previously analysed by the authors, often conducting a parallel physical modelling comparison, thus allowing a performance evaluation. This presentation describes how the authors obtained results and/or reduced uncertainty. Topics such as meshing strategy, turbulence model selection and parameter calibration are addressed.
Pushing the air entrainment and drift flux models to their limits
Boris Huber, Vienna University of Technology
To avoid cavitation damage, spillway chutes with high flow velocities must be aerated. This can be done with an aerator, consisting of a step and a deflector. Several aerators with different step heights, deflectors and spillway chute’s inclinations were simulated with FLOW-3D and compared to hydraulic model tests.
Witka Barrage case study
Oscar Herrera-Granados, Wrocław University of Technology
In this study, the application of two water flow numerical models (one of them, the FLOW-3Dstandard k-epsilon model) is presented in detail. The functionality of the existing Ogee spillway, which was not destroyed in 2010, and the new labyrinth weir, is tested. In addition, the output of the numerical models is compared with the experimental works performed at the Wrocław University of Technology. The experiments demonstrated that the draining capacity of the new alleviation scheme is sufficient for catastrophic conditions if water is flowing under steady flow. Nevertheless, the temporary cofferdam, that was part of the reconstruction work, is severely affecting the draining capacity of the entire barrage project, most of all, the draining capacity of the Ogee weir.
3D numerical modelling of the Mohelno Reservoir
Tomas Studnicka, Marek Cejda and Jiri Svancara, Poyry Environment
The Mohelno Reservoir on the Jihlava River forms an inherent part of the Dalesice waterworks. With a total storage of 17.1 million m3, it balances the runoff from the Dalesice Pumped-Storage Hydroelectric Power Station, and serves as its lower basin for pumping. As a result, the water level in the Mohelno reservoir fluctuates up to 12 meters during 24 hours. Moreover, the Mohelno Reservoir provides cooling water for the nearby Dukovany Nuclear Power Station, and also receives its waste water. Currently, waste water is being discharged on the water surface next to the cooling water intake structure (CWIS). Significant water quality deterioration at the CWIS has been detected particularly during longer periods when the water level in the Mohelno Reservoir has been held close to the minimum operating level. A numerical model of the entire Mohelno Reservoir has been built to gain a better understanding of the flow patterns in the Mohelno Reservoir and to test various locations of releasing waste water in order to improve water quality at CWIS.
Dam break simulation and flood routing using a hybrid modeling approach
Randy S. Lagumbay, John E. Richardson, Cindy How and Timothy A. Harmsen, ARCADIS-US
A three-dimensional (3-D) Computational Fluid Dynamics (CFD) analysis was used to simulate flooding caused by failure of the Wauseon Upground Reservoirs. The primary objective of the study was to evaluate the downstream effects of a reservoir failure. A 3-D, CFD, model of the Upground Reservoirs and surrounding topography (approximately 10 miles radius) was constructed and used to simulate flood movement in the event of a failure. In this study, a hybrid approach was used due to the size of the computational domain. A fully 3-D modeling approach was used in the vicinity of the reservoir and a depth-averaged modeling approach was used away from the reservoir downstream. The results of the analyses were used to determine the maximal extent of inundated areas and to determine time factors associated with flood movement downstream. At the conclusion of the study, inundation maps were developed and included in the city’s Emergency Action Plan.
Falling water, an exploration of combined air and water flow in a simplified geometry
Laurent Bilodeau, Hydro-Québec
A cubic basin of water emptying sideways into another one provides a very basic geometry for exploring FLOW-3D’s capabilities for modeling a plunging water flow. This simple case is run with water as a single fluid system, and water and air as a two fluid system, with a variety of options and spatial resolutions. A number of simulations will be presented with animations and discussed.
Intrusive gravity currents interacting with obstacles in a continuously stratified environment
Jian Zhou and Karan Venayagamoorthy, Colorado State University
The flow dynamics of intrusive gravity currents past a surface-mounted obstacle were investigated using large eddy simulations. The propagation dynamics of a classical intrusive gravity current in the absence of an obstacle was first simulated to validate the numerical simulations. The numerical results showed good agreement with experimental measurements. An obstacle with a dimensionless height of ̃ = / ( the total fluid depth) was then introduced and acted as a controlling factor of the downstream flow pattern. It is found that for short obstacles, the intrusion re-established itself downstream in a form similar to the classical intrusion (in the absence of an obstacle). However, for tall obstacles, the downstream flow was found to be a joint effect of horizontal advection, overshoot-springback phenomenon, and the Kelvin-Helmholtz instability. Three regimes of downstream obstacle-affected propagation speed were identified depending on values of ̃, i.e. a retarding regime ( ̃ ≈ 0~0.3), an impounding regime ( ̃ ≈ 0.3~0.6), and a choking regime ( ̃ ≈ 0.6~1.0). This work highlights the significance of topographic effects in stratified flows with horizontal pressure forcing, and aims at providing a preliminary guidance for the engineering design of retarding facilities for intrusive gravity currents.
Maple River Aqueduct – Detailed hydraulic modeling
Andy McCoy, HDR
The U.S. Army Corps of Engineers (USACE) in cooperation with non-Federal sponsors completed a feasibility study to develop, evaluate, and compare flood risk management alternatives for the Red River of the North (RRN) around the Fargo-Moorhead Metropolitan (FMM) area. The selected plan is a diversion of the Red River to the west of Fargo. Detailed hydraulic design of the selected diversion and its associated structures is now progressing and will lead to plans and specifications (P&S). At the location where the Maple River crosses the diversion, complex hydraulic conditions are anticipated. An aqueduct, spillway, and channel re-alignment are all part of the crossing. HDR, as part of a joint venture with Hanson and Bergman, and in partnership with the University of Minnesota, Saint Anthony Falls Laboratory (SAFL), has been working with the St. Paul and Rock Island Districts and the local sponsors to investigate the performance of the Maple River aqueduct crossing using physical and numerical modeling to further develop the Maple River aqueduct hydraulic design criteria. The numerical model FLOW-3D was validated against the physical model, providing the basis for the hydraulic investigation. The result of the detailed modeling effort resulted in a confirmation of the structure type, optimization of the aqueduct sub-structure design, and spillway design.
Modeling efforts at Reclamation’s hydraulics laboratory
Bryan J. Heiner, USBR
The Bureau of Reclamation has a long standing history of both physical and numerical modeling of hydraulic structures. Both modeling techniques provide individual strengths and weaknesses. Many of the limitations of one modeling effort can be complemented by the other and vice versa. This presentation discusses examples of modeling performed at the Bureau of Reclamation’s Hydraulic Laboratory in Denver, CO where FLOW-3D has been used. Both solely numerical and composite modeling (numerical and physical modeling) efforts will be discussed.
Niagara hydro power project modeling and flow simulation
Jiankang (Jay) Zhu, NYPA
The New York Power Authority’s Niagara Project includes the Robert Moses Niagara Power Plant (RMNPP) and the Lewiston Pump Generating Plant (LPGP). Two intakes are located on the Niagara River, upstream from Niagara Falls. Water flows by gravity through two underground conduits into the forebay. LPGP pumps water from the forebay into the Lewiston Reservoir or provides generating flows into the forebay. LPGP typically operates to provide additional on-peak generation, to provide storage for future generation, and/or to balance diversion flows from the Niagara River. Due to its complexity, Niagara Project has difficulty to precisely measure/calculate the diversion flow. The existing flow measurement/calculation showed a few thousand CFS difference in some scenarios. The inaccurate flow data might have caused control errors and impacted the operational performance. Continuous efforts were made to improve the quality of the flow data. The flow calculation was adjusted and the advanced water level/flow measurement instruments were applied. Starting in 2012, FLOW-3D was used to set up the CFD model for the entire Niagara Project to better understand the flow conditions. The model included the forebay, two hydro power plants and two 4-mile-long underground conduits. The large size of the model and the need to simulate long term plant operations made it necessary to apply FLOW-3D/MP on a 64-core high performance cluster, which greatly reduced the computing time. Water level/flow under variant operation conditions were simulated, which served as a critical reference to verify and evaluate the existing flow calculation and measurement.
Practical dam breach analysis using FLOW-3D for flood routing
Francis Filion, Golder Associés Ltée
The presentation will feature the case study of a multiple dam breach analysis (DBA) for a project located in northern Québec. FLOW-3D was used to model the flood routing of the dam failures and determine the potential impacts of such failures to the environment and a bridge located downstream of the mine site. Numerous potential failure modes and locations were analyzed including cascading dam failures. This was done using a practical, quick and efficient approach, which Golder developed. A series of generated DBA flood routing maps from this particular project and others that Golder worked on are displayed to show the high quality of the final product. To portray the great potential of using FLOW-3D in DBA flood routing, a more complex DBA project is presented and its challenges discussed. In this project a non-Newtonian fluid is used to model more accurately the potential failure of a tailings retention dam on a mine site. To conclude, features likely to improve the current methodology are introduced.
Stepped spillway flow over small embankment dams: Some computational experiments
Inês Lúcio1, Inês Meireles2, and Jorge Matos1
1University of Lisbon, IST, 2University of Aveiro
In the last decades, urban development in the vicinity of dams, such as embankment dams, has led to hazard classification changes. Inadequate spillway capacity, which may result in embankment overtopping, can be considered a relevant deficiency. Roller compacted concrete (RCC) stepped spillways have been frequently used for providing overtopping protection and increased spillway capacity for these dams. An increased demand for stepped spillways applied to embankment dams has led to increased research efforts on the knowledge of the flow properties on stepped spillways. FLOW-3D possesses the capability of simulating the boundary layer development and point of inception of air entrainment on highly turbulent chute flows, along with the related turbulent flow properties. In this study, results of FLOW-3D are compared with those acquired on an experimental facility representative of a small embankment dam providing for safe overtopping, by means of a 1V:2H sloping stepped chute. FLOW-3D simulations (2D) were performed for various discharges using the κ-ε RNG turbulence model, and the results were compared with available experimental data, including flow depths, velocity distribution and energy dissipation. Such main flow properties are of great relevance for hydraulic design purposes. In general, a good agreement between numerical and experimental data has been achieved in the non-aerated flow region. However, the precise CFD modeling of the self-aerated flow region remains a challenge.
Using CFD for the evaluation of inlet distribution channels
Steve Saunders, Ibis Group
In both potable and wastewater treatment plants, there are often multiple treatment trains running in parallel. This is typical of settling basins and combined anoxic zone – oxidation lanes and is done in the interest of space economy. Having parallel treatment trains is also a practical means of handling a wide range of through-flow rates where a basin or basins can be taken out of service to ensure that the in-service trains are operating at their design levels. A key to the efficient operation of parallel treatment trains is in the design of their inlet flow distribution channel. The design objective is to have the inflow distributed equally among the in-service trains. To that end, a distribution channel may employ a feature like a varying cross sectional area to help maintain a common approach velocity to the individual trains. Often, velocities are low and the water surface in the channel is nearly planar, thus leading the CFD practitioner to consider employing a simple rigid lid as the air/water boundary condition. However, subtle variations in water elevation may have a profound effect on flow distribution. Therefore, a free-surface boundary condition becomes critical to achieving a representative simulation. This presentation discusses using FLOW-3D for the evaluation of several distribution channels where variation in water surface elevation plays a significant role in the simulation results.
Vortex identification using streamlines, vorticity and Q-criterion
Javier Patarroyo, SNC Lavalin
One of the biggest challenges when studying vortex problems in CFD is to be able to identify, evaluate its strength and/or to determine the type of vortex according to the vortex classifications (Type 1 to 6) as defined by ASCE, 1989. Usually this type of classification is done with a physical model by visual observation with the aid of colored dye. FLOW-3D offers some methods to aid in the vortex detection, namely, streamlines, vorticity and Q‑ Criterion. In general, the use of streamlines to detect vortices is intuitive and depends if the rotational patterns can be detected on different planes. By using the vorticity and the Q-criterion parameters, it is possible to narrow this search and locate the streamlines closer to detected cores. To qualify the vortex strength, it is imperative to have a correlation between the simulated vortex strength and the real vortex strength, whether in a physical model or in a prototype. In this presentation, different cases will be discussed showing how the use of streamlines, vorticity and Q-Criterion aided in the vortex identification. Furthermore, for one case, a vortex risk matrix was developed to qualify the vortex strength using photographs taken on site with known operating conditions.
A comparison of pump sump modeling using FLOW-3D
Stephen Saunders, IBIS Group
Large pump stations often require that a model study be performed prior to their designs getting approval for construction. The impetus behind this analysis is the life cycle cost of a station that needs to provide efficient and reliable service for what could be decades of operation. Scale physical modeling has been an industry standard for over 100 years, however, CFD simulation is gaining acceptance as a viable alternative. The challenge is not so much a question of the utility or accuracy of CFD solutions, but one of overcoming the inertia within the pump industry. This is an industry whose approach to model testing is conservative and has changed little in the past decades. Today, most CFD practitioners approach a pump station assignment by emulating a physical model knowing that the results obtained, if presented in the language of the physical modeling world, will have the best chances of being accepted by the client. The vast data files produced through CFD modeling along with the ability to access every corner of the model domain with a few key strokes means CFD simulation has the potential of being much more than just an emulator of physical models. FLOW-3Dwith its superior VOF model and the rapid adaptability of the FAVOR™ meshing scheme give it some distinct advantages as a choice of code for pump station modeling. This presentation is based on a sample pump station model that will be used as a means of comparison between the results obtained from FLOW-3D and some other popular CFD codes. Mesh resolutions of the cases are matched as closely as possible as are the discretization schemes and turbulence models.
Alternative methods for the implementation of trash rack losses
Michael Waldy, Roman Gabl, and Markus Aufleger, University of Innsbruck
Trash rack bars are relatively fine structures in front of an intake. In many simulations the effects of those obstacles are neglected to reduce the needed grid elements and computational time. In the presented work, alternative approaches for the implementation of trash rack losses are investigated. Therefore, two different model assumptions are used: (a) baffles and (b) porous media. Both are verified with a real trash rack based on a very fine grid and with the help of theoretical approaches. Afterwards, the resolution of the grid is reduced. The results show that porous media are a good way to model such trash rack losses.
Analysis of round-crested overflow spillway using physical and numerical modeling
Tomáš Studnička, Pöyry Environment a.s
The presentation describes the results of basic hydraulic research on round-crested overflow spillways, which are characterized by relatively high capacity and are widely used. Using physical modelling, the impact of weir crest length, model surface roughness and model scale on water discharge capacity has been analyzed. As a part of the research, investigation of pressure distribution along the spillway has been carried out. For selected scenarios, results of physical modelling are compared with results obtained by means of numerical modelling. Numerical simulations have been performed for various mesh, physics and numerics setting (e.g., cell size, turbulence model, momentum advection method) and its impact on nappe shape and pressure distribution along the spillway is analyzed.
Computational dam break analysis using PMF from statistical downscaling
Fahid Abbas and A. GÜVEN, Gaziantep University
Dam failure can be catastrophic if the structure is breached or significantly damaged. The main causes of dam failure include inadequate spillway capacity, piping through the embankment, foundation or abutments, overtopping and spillway design error. Large dams are designed based on Probable Maximum Flood (PMF) determined from gauged data using flood frequency analysis. In the past most of the existing dams were designed based on limited available hydrological data. Global warming and climate change caused an observed change in the hydrological data; therefore, forecasters need re-calculated scenarios in many situations. Downscaling, which is a reduction of time and space dimensions in climate models, will probably be the future of climate change research. However, it may not be possible to redesign an existing dam but at least precautionary measures can be taken for the worse scenarios of flood in the downstream of the dam location. The purpose of this study is to develop a new approach for computational dam break analysis, using FLOW-3D, based on predicted PMF from statistical downscaling. Attempts were made in order to evaluate the impacts of the global warming and climate change on determining of the flood discharge by considering different scenarios of General Circulation Models.
CFD modeling of a thermal buoyant plume
Navid Nekouee1, John Wendelbo2, and Adwaith Gupta2
1Tetra Tech, 2Flow Science
The nearshore dynamics of the Grand River Plume have been studied using FLOW-3D. The model results have been compared with extensive field studies to verify the accuracy of hydrodynamic predictions and the non-buoyant spreading effects of these types of density-driven currents. FLOW-3D has an advantage over other plume models because it accounts for the nonlinear accelerations at the boundaries of the plume. FLOW-3D can also reveal the flow information (velocities and densities) in all three dimensions and for a larger spatial scale. It can better represent the flow transition from near field to the far field. It solves the Navier Stokes equations including detailed free-surface dynamics, in 3D with a number of advanced turbulence models. With the advancements in computing technologies and runtime reductions, CFD models are becoming valuable tools in representing complex hydrodynamic processes such as buoyant plumes.
An attempt at providing a simplified method to predict risks of vortex formation
Amaury Pittion-Rossillon 1, Grégory Guyot1, and Antoine Archer 2
1 EDF-CIH, 2 EDF-R&D
The understanding of complex phenomena in hydraulics has often relied on physical modeling for industrial purposes. EDF has been challenging some of those issues with 3D CFD code FLOW-3D for six years, and wishes to apply it to vortices detection. The main difficulty in using finite elements programs is the relevance and stability of their numerical results. In the field of vortices, it has been decided to test how reliable FLOW-3D and its VOF method are. This study is based on a schematic hydraulic experimental model realized in the EDF-R&D laboratory. The chosen case is a simple configuration of a vertical downward drain hole. The basin is one meter long and around a half meter wide. The water level is fixed and the flow rate is adjustable. The main advantage of this experiment is that the geometry is easy to simulate with 3D CFD software. In this configuration it is ensured that a free vortex phenomenon does exist. Different types of vortices have been chosen for the validation case. The aerated vortex length for the maximal case reaches the basin bottom. The first goal of the 3D CFD simulation is to check if FLOW-3D is able to represent a vortex when it physically exists.The second objective is to find a simplified method that enables the representation of the vortex as it appears in the physical experimentation.The third one is to propose a numerical method that allows the engineer to predict the vortex type for the preliminary design of a hydraulic structure.
Failure of Niedów Dam in Poland – Preliminary analysis and conclusions
Bernard Twaróg, Cracow University of Technology
A disastrous flood occurred in 2010 at the Niedów reservoir (capacity 4.8 hm3) on the river Witka, south of the town of Zgorzelec (Görlitz). An extreme wave occurred with an estimated volume of 30 hm3. Overflow of the wave crest caused the failure of the earth dam. Catastrophic outflow flooded the villages of the Witka valley. Analysis of the causes and effects was performed with FLOW-3D. The simulation results and analysis will be presented during the conference.
Fish Ladder – Find the entrance (River Iller, Germany)
T. Liepert and P. Rutschmann, Department of Hydraulic and Water Resources Engineering
The project site is located at the river Iller in Germany. The operating company is going to do some refurbishment works on the existing power plant. The engineers want to install new turbines which are optimized for the given situation. The permission to do this requires that the works done at the plant comply with the European Water Framework Directive. This means that the ecological situation has to be improved – in this special case the circumstances for fish migration have to be enhanced. Therefore the operating company is planning to build a new fish ladder, which will allow the fish to move upstream. During the planning phase, various technically possible solutions were designed by the civil engineers. However, the essential question if the fish will find the entrance of the fish ladder, could not be assessed easily. To answer this question, a 3D-numerical model was created. Thus it was possible to simulate different configurations and positions of the fish ladder using various operating states. In collaboration with a fish expert, the numerical results were used to find the best solution for the new fish ladder entrance. One crucial point was the communication between the engineer and the biologist. The results had to be post processed in a way that enabled the biologist to gather the information he needed for his decision.
Numerical approaches for the prediction of head losses incurred over spoiler baffle arrays for use in slip-line rehabilitated fish passage culverts
Jason Duguay and Jay Lacey; Université de Sherbrooke
In this study, FLOW-3D was employed to determine the hydraulic head losses incurred over various arrays of spoiler baffles placed along the invert of a full flowing slip-lined highway culvert at moderate Reynolds numbers (1.1e5 – 2.3e5). Spoiler baffles are used to improve hydraulic conditions for a fish passage through roadway culverts. Two head loss calculation approaches were implemented. As a first approach, FLOW-3D‘s porous baffle functionality was used to determine the variation in flux averaged total hydraulic head incurred over a short baffled test section. As a second approach, a force balance of pressure and shear forces applied on each individual baffle was employed to determine pressure drops over the test section. The former approach has the advantage of providing spatial distributions of drag coefficients. The force balance approach demonstrated substantially less error in head loss predictions than the former compared to experimentally obtained values. Drag coefficients of the individual spoiler baffles demonstrated agreement with experimental values. This presentation explains and discusses both head loss prediction approaches and sheds light on the potential of FLOW-3D to determine head losses developed over isolated 3D bluff bodies.
Outlets and spillways – More capacity with FLOW-3D
Jakob Seibl, Roman Gabl, and Markus Aufleger, University of Innsbruck
Different types of outlets and spillways were investigated at the Unit of Hydraulic Engineering at the University of Innsbruck. Each project had a completely different hydraulic design and scope of the investigation. In the presentation we want to give a short overview of the main projects in the last two years and highlight the advantages of FLOW-3D for each one.
Simulation of flow over an ogee-shaped dam
Doug Joy, Ning Pan, and Xinqiao Cai; University of Guelph
This study presents the comparison of the flow over an ogee-shaped dam using FLOW-3D and a physical laboratory-scale model for the evaluation of numerical model performance. In the physical experiment, an ogee-shaped dam was modeled in Solidworks and printed using a 3D printer. The dam was put in the flume, and the data of water surface elevation and flow velocity were collected and compared with the results from the numerical model. In the numerical model, FLOW-3D was used for the simulation of the flow under the same conditions as the physical model. The numerical model used the finite volume method to solve the RANS equation. The motion of free surface was tracked using the volume of fluid (VOF) method. The simulated results matched well with the data collected from the physical experiments. This confirmed that the numerical model is an advanced tool to assist the design in hydraulic engineering.
The new sediment module in FLOW-3D version 11
Markus Grünzner and George Wei, Flow Science
This presentation shows the capabilities of the new sediment model in FLOW-3D version 11 and presents some results analyzed with the new post-processor FlowSight. It also gives an overview of the new hybrid mesh generation possibility. The hybrid approach is a combination of the shallow water model and the full 3D meshing. It is a challenge to simulate sedimentation and erosion processes in reservoirs and basins in one full model. Due to the size of catchment and storage areas/volumes of the reservoirs and the necessary high resolution near the barrier, in most real cases it is impossible to set up one full three-dimensional numerical model to simulate the processes of sediment transport. Several examples are presented to give an overview of the model capabilities. This presentation is a roundup of the special hydraulics training given at this user meeting.
Three-dimensional subaerial landslide generated wave simulations
W. Daley Clohan; University of British Columbia
Numerically simulating the highly complex real-world phenomenon of subaerial landslide generated waves (SLGW) is one of the most challenging hydrotechnical simulations to get ‘right’. As such, there are very few (or no) readily available numerical models that have been validated for reproducing this phenomenon as a whole. This study focuses on investigating FLOW-3D solutions for SLGW and advancing the continuing effort of numerical validation. Specifically, this work aims to quantitatively compare three-dimensional simulations against high-fidelity physical free-surface model data. The results of which indicate that using the default settings, FLOW-3D performs very well at generating and propagating waves, but tends to generally over-predict maximum wave run-up elevations. Deviating from FLOW-3D default settings, and adjusting several key settings can notably improve the outcome without overly impacting runtimes. For this test case, accuracy of the momentum advection solver is of particular importance. For example, using a second-order momentum advection scheme over a first-order scheme reduced the maximum wave run-up error by about 1.5 times. The results of this work provide not only insight into which FLOW-3D settings may provide better results for SLGW simulations, but also the underlying physics that pose the most grief to such simulations.
Turbulence analysis in a stilling basin through a mathematical simulation in FLOW-3D and an experimental technique with ADV
Víctor Ignacio Mastache Mendoza and Jesús Gracia Sánchez; Universidad Nacional Autónoma de México
In this research, a turbulent flow was characterized in a stilling basin of the Río El Salto’s physical model, with pre-established design conditions. The velocity of water was measured with an Acoustic Doppler Velocimeter (ADV), along the stilling basin and at different depths in order to determine the length of the stilling basin. Also, the stilling basin was modeled in FLOW-3D with the same dimensions and design conditions of the physical model in order to compare the behavior of turbulence in both models (physical and mathematical). Velocities were compiled and statistical parameters, such as resultant velocity, turbulent kinetic energy, and turbulence index were calculated. The results of the experimental technique with ADV demonstrated that the required stilling basin length was 1.20 m, in contrast to a 1.75 m length calculated with traditional empirical design. Simulation in FLOW-3D determined a smaller turbulence scale. According to the statistical parameters, the greater turbulence finished approximately at 0.8 m length. However, due to lack of variability or fluctuations in results, this information is not comparable with the one obtained in the physical model. This emphasizes the limits of the current mathematical model. Finally, it was concluded that the ADV experimental technique, commonly studied in recent years, is appropriate to characterize turbulent flows and that numerical methods like FLOW-3D are reliable when supplemented with physical models.
Using FLOW-3D to increase grit capture in an underperforming vortex grit chamber
Ryan Edison, AECOM
In wastewater treatment, an important aspect of treatment is the removal of grit prior to biological treatment. For many larger utilities, the management of grit is very costly if not removed efficiently at the upstream end of the treatment plant. During the design of treatment plants the percent required of grit removal is established, but often the as-built realities are vastly different. FLOW-3Dwas used to investigate ways of improving the removal efficiency of grit in such an as-built situation where the coarse grit removal target of 95% was actually only 77% based upon testing and grit characterization performed by the utility. AECOM developed a FLOW-3D model of the as-built vortex grit tank. After validation to hydraulic grade line (HGL) measurements, it was used to investigate the impacts of internal baffling, propeller rotational speed, grit hopper cover, guide vanes, and downstream channel modifications. The study concluded with specific recommendations to improve grit removal. Once adopted by the utility, they saw an increase grit capture of 17% – to within 1% of the coarse grit removal target of 95%. FLOW-3D modeling involved the use of the particle sub-model to simulate grit and the movable mesh model (GMO) to simulate the central, rotating impeller. Of particular interest was the demonstration that initial results, with no calibration (“out of the box”) effort, matched the provided HGL measurements and also accurately predicted the location of a well-established hydraulic jump within the system.
3D modeling of a street flow crossroad
Miguel de Ros Casacuberta and Manuel Gómez Valentín, Leonardo Nanía, Manuel Gómez; UPC. Barcelona Tech, Flumen Research Institute
The study of street flow in crossroads is still a subject of great interest in urban hydrology. Cities have grown both in number and size, and the study of urban runoff has become increasingly relevant. In recent years, natural events have highlighted shortcomings of the existing drainage infrastructure to capture urban runoff, so urban flooding increases. The particularity of the unsteady flow of urban runoff lies in two aspects: a high width/depth (aspect ratio), and a three-dimensional nature when the crossroad is reached. These reasons make it necessary to consider a three-dimensional study of the flow pattern as well as the influence of three-dimensional flows on the distribution of the flow between output streets. From the first approach of Nanía (1999), where the hydraulic behaviour of a supercritical flow in the street crossing was analysed considering experimental measures on a physical model, different studies with two-dimensional models have been done (Bonet, 2006) (Martinez, 2011). In the three-dimensional field, the first study was done by Mignot (2005). He applied a scale model to study the structure of the flow, complementing Nanía’s previous studies. The aim of this presentation is to develop a study of the flow pattern in a street crossing with a 3D code (FLOW-3D), comparing the results with those of a 2D model (code Iber), and with the available results of the physical model. The performance of the different approaches and the added value of a 3D code in these types of studies are analysed.
3D hydrodynamic computational modeling for the São Roque hydropower plant project
Diego David Baptista de Souza, Alexandre Charles Allain and Anaximandro Steckling Muller, Engevix Engenharia S/A
The São Roque hydroplant project is located in Brazil, in the State of Santa Catarina, on the Canoas River. A roller compacted concrete dam allows an installed capacity of 141,9 MW. Several 3D computational models were carried out on with FLOW-3D in order to evaluate some issues regarding the engineering design. These studies are presented on this work.
Analysis of the flow structure in aerated hydraulic jumps using physical and numerical modeling
Valero Huerta, D., García-Bartual, R., Fullana Montoro, O., Andrés Doménech, I., and Vallés Morán, F.J.; Institute of Water and Environment, Polytechnic University of Valencia
A hydraulic jump is the rapid transition from supercritical open channel flow to subcritical flow. Hence, the rapidly flowing liquid is abruptly slowed, while flow depth increases, converting some of the upstream kinetic energy into potential energy. An important amount of energy is irreversibly lost due to the turbulence generated. Interaction of such turbulence with air at the free surface produces air volumes trapped into the flow. In this research, several hydraulic jumps in a wide range of Froude numbers are modeled physically and numerically. Furthermore, experiments using air entrainment devices have been carried out, to check the effect of artificially aerated flows in the hydraulic jump properties. The new multiphase flow properties and associated energy dissipation are analyzed. These artificially aerated hydraulic jumps, where the bubble cloud interacts strongly with water, are found to have different dissipation rates. This fact can yield important potential benefits in practice, e.g., operation of hydraulic works designed for energy reduction of the flow in stilling basins at large dams. The FLOW-3D routine for turbulent air entrainment is used, coupled with variable density evaluation. The RNG turbulence model is also employed in the numerical modeling. Simulations are firstly performed in a calibration stage of the air entrainment model, being later compared with the physical model. Interesting conclusions are obtained about flow patterns and internal features within the hydraulic jump under different initial aeration conditions of the supercritical upstream flow.
Complementary spillway of Salamonde dam – physical and 3D numerical modeling
Miguel Silva, António N. Pinheiro; Technical University of Lisbon, António Muralha, and Lúcia Couto; Laboratório Nacional de Engenharia Civil
Throughout the planning and design of hydraulic structures, engineers and researchers are increasingly integrating computational fluid dynamics (CFD) into the process. Despite reports of success in the past, there is still no comprehensive assessment that assigns ability to CFD models to simulate a wide range of different spillway configurations. The complementary spillway for Salamonde dam, located in the north of Portugal is a gated spillway, controlled by an ogee crest, followed by a tunnel with rather complex geometry, where free surface flow was considered, and a terminal structure which directs the jet into the river bed. The present paper analyzes the ability of a CFD model (FLOW-3D) to simulate the flows along this spillway. The spillway was primarily tested and developed in a physical model built in National Laboratory for Civil Engineering (LNEC), where discharge and flow depth were recorded in ten defined cross-sections for four different gate openings conditions.
Estimating gate forces
Wade Moore and Justin Bartels, MWH Global, Inc.
The rapid closure of emergency gates at the upstream end of a penstock(s) at a hydropower plant can generate large forces on the gate and negative pressures within the penstock. FLOW-3D can be used to simulate various closure scenarios and provide directly the forces on the gate and the data needed to compute the air venting requirements to prevent penstock collapse. FLOW-3D was recently used on the design of a 36 MW power plant to simulate the closure of the upstream emergency gates during an uncontrolled unit runaway and the subsequent closure of the wicket gates when control is restored. During initial closure the penstock is partly drained drawing air in through the vent and then rapidly refills when the wicket gates close. The return wave from the closure impacts the gate generating a large upward thrust that must be taken into account in the design of the gate support structure.
Hybrid model tests for the Dal HEP (Nile River, Republic of Sudan)
T. Liepert, and P. Rutschmann; Department of Hydraulic and Water Resources Engineering, and R. Huber; Hydraulic Laboratory Obernach (VAO)
The project site is located on the river Great Nile in Sudan. The project site is characterized by a series of mid-river islands of various sizes, thus it is quite complicated to model the hydraulic situation in a proper and cost-efficient way. To overcome this problem the concept of hybrid modeling was used. The combination of physical and numerical models allows the model tests to benefit both methods.  The physical model was conducted by the VAO in Obernach, as the numerical model has been computed at the department in Munich using FLOW-3D. Spillway capacity: The capacity determination of only one or two opened bays was done both numerically and physically. The comparison of both models shows a quite high similarity. The maximum flood event could only be investigated numerically, as the physical model discharge is limited. Moreover, FLOW-3D was used to gain detailed information about the spatial flow field. Pressure heads on weir back: For numerous situations the pressure heads were measured in the physical model. The maximum underpressures that were occurring on the weir back can be accepted. The results are in good agreement with those numerically determined by the numerical model. Furthermore, a shape optimization of the underflow spillway was conducted numerically. The results show the physical and numerical determined measurements fit together well (qualitative and quantitative). Hybrid models are outstandingly suitable for model tests of such huge hydraulic structures.
Modeling and detecting vortex with 3D CFD
Amaury Pittion-Rossillon, Grégory Guyot; EDF-CIH and Antoine Archer; EDF-R&D
So far, the understanding of complex phenomena in hydraulics has relied on physical modeling. EDF has been studying some of those issues with FLOW-3D for six years, and wishes to apply it to vortices detection. Following the work that EDF presented at the 12th European Users Conference, on the benefits of FLOW-3D and physical model for vortices, this study aims at challenging further the reliability of FLOW-3D in this field.
This study starts from:
- a schematic experimental model realized in EDF R&D laboratory, simulating a stable vortex in a rectangular tank (one meter length and about half a meter width) by water discharge through a bottom-located outlet conduit, with a fixed water level and an adjustable flow rate;
- previous EDF works on vortices using FLOW-3D, reproducing the experimental model, providing sensitivity analyses on the sets of parameters allowing vortex emergence (momentum advection order, turbulence model, and VOF advection).
It aims at:
- improving the stability of the current FLOW-3D vortices model developed at EDF, which do not succeed in preserving a constant water level in the tank due to numerical losses;
- testing an alternative approach for imposing the boundary conditions, so as to optimize the size of the model;
- implementing vortex identification criteria commonly found in the literature in order to provide a comparative study of their efficiency on FLOW-3D such as Q invariant, swirling strength, and λ2 criterion).
The numerical results will be compared to the experimental measurements in order to determine their accuracy.
Numerical modeling of flows in pool-type fishways equipped with bottom orifices
Ana L. Quaresma; Instituto Superior Técnico, Technical University of Lisbon and António N. Pinheiro; CEHIDRO, Instituto Superior Técnico, Technical University of Lisbon
Rivers’ longitudinal connectivity is compromised by man-made obstacles such as dams and weirs which affect fish movements leading to population decrease and genetic deterioration. If properly designed, fishways re-establish connectivity allowing for fish migration. The aim of our work is to develop efficient pool-type fishways. Modelling free surface flows in hydraulic structures with complex geometry, like pool-type fishways, with aerated and complex flow patterns, represents a significant research challenge. Knowledge already acquired in an experimental full scale indoor pool-type fishway in previous studies is used. A 1:2.5 scaled fishway of this facility was built and used to characterize velocity and turbulence in a pool-type fishway with cross-walls equipped with bottom orifices. An offset orifice configuration was used with consecutive orifices positioned on opposite sides of the cross-walls, creating a sinusoidal flow path. An acoustic Doppler velocimeter (ADV) device was used to measure three-dimensional velocity components (x,y,z) of flowing water. A 3D computational fluid dynamics (CFD) model of the fishway was built using FLOW-3D. The numerical model was calibrated with the experimental data obtained with the ADV measurements. Parameters that influence fishways’ efficiency like velocity fields, turbulence, kinetic energy and Reynolds shear stress were determined and compared with the ones determined from ADV measurements and results deviations between experimental and numerical data were analyzed.
Simulation of fate and transport of fecal indicator bacteria (FIB)
Kordula Schwarzwälder; Technische Universität München
We have an ongoing DFG research project to get a closer look on the fate and transport of so called fecal indicator bacteria (FIB) in the river Isar and the effect of the biofilm on the kinetics of these bacteria. With the results of our experimental work we are programming a module which should enable us to simulate the analysed processes of fate and transport of bacteria and their interaction with the biofilm and to use this tool, at the very end, for prediction of water contamination. Factors of influence, which have to be considered in the module, are UV-inactivation of the bacteria, the turbidity of the water, the biofilm itself and the amount and size of other particles in the bulk phase that the bacteria can be attached to. Compared to freely suspended bacteria, the sorption changes the preconditions for the sedimentation of bacteria onto and into the biofilm and its re-suspension back into the bulk phase. These factors have to be considered according to the data measured in the experiments. We are using the Scalar and Chemical models in FLOW-3D to attach the bacteria module. Depending on the quality of the data of the experiments we will use the Particle model in FLOW-3D for a more accurate simulation of a single bacteria.
Uniform flow, sudden closure of turbines and discharge of overflow by stepped spillway in a hydropower plant
Anıl Olgaç and Filiz Yazıcılar Gözütok; Doğru Engineering Limited Co.
Power channel, side spillway, side spillway channel, discharge channel, stepped spillway channel, headpond and penstock of a hydropower plant are defined in one domain in FLOW-3D. The water level rise in case of a sudden closure of turbines and discharge of excess water through the side spillway is simulated for this configuration. Uniform flow conditions are provided in the simulation, which is the start position of the system. Effective parameters are identified to provide uniform flow. Sudden closure of turbines are simulated by stopping the outflow of the system. Water rise is observed to march through the headpond and power channel to the upstream part of the power channel. When it reached the side spillway on the power channel, the side spillway spilled the water to the side spillway channel and to the discharge channel (connecting the side spillway channel to the stepped spillway channel). Energy of water is dissipated by the stepped spillway and released to the river. In this study the flow regime before the stepped-spillway is supercritical, which is different than most applications of stepped spillways. Flow does not reach critical depth at the start of stepped spillway. Flow regime remains supercritical before and after the stepped spillway.
In this study;
- The system is evaluated in hydraulic means and structures are designed according to the simulation performed by FLOW-3D. Construction has already started, where it will be commenced within 2 months after test stage.
- Providing the uniform flow conditions in FLOW-3D is discussed and learned.
- In the case where the domain is huge as in this study, it is urgent to break the domain into pieces. Grid overlay boundary in FLOW-3D is used for these cases. However, “grid overlay” boundary was insufficient in our case. Because “grid overlay” cannot transfer the output of a domain to the neighboring domain as input in the “same” time interval. Therefore it was necessary to work in one domain in this study, although the duration of runs were considerably longer.
Validation of a hybrid 3-dimensional and 2-dimensional numerical flow modeling technique for an instantaneous dam break
David Souders1, Jeff Burnham1 and Jayesh Kariya2
1Flow Science, 2 Flow Science Software Pvt. Ltd.
Flooding due to dam failure can have catastrophic consequences and is of significant concern to dam safety professionals. A number of methods have been developed for predicting the outcome of a dam breach including flow behavior, inundation locations and depths, and possible damage and loss of life. Computational fluid dynamics (CFD) is one of the most cost-effective options in the water and environmental industry for modeling catastrophic conditions and validating designs for safety and environmental criteria. CFD proves especially useful wherever flows are complex and difficult to approximate with physical models.
Application of empirical constants for the eddy viscosity on the wake and jet
Young Jun Cho and Il eum Park; Chonnam National University
Wakes and jets that have analytical solutions were materialized and the most appropriate application range of major empirical constants was discussed using various turbulence models of the eddy viscosity concept. Relatively accurate accordance was shown by analytical solutions of wakes and jets when compared to various values of physical modeling, and they were used as reference index for all numerical modeling results. In the wake experiment with FLOW-3D, zero-equation model showed similar results for wake width and drag coefficient as analytical solutions and physical experiment values. However, absolute mean error and maximum velocity difference for all calculated cases were over-valued and appropriate eddy viscosity coefficient was not computed on the back of resistance body. Wake was not materialized appropriately using zero-equation model. One-equation model accurately materialized wakes when appropriate L was selected, because wake width, maximum velocity difference and drag coefficient accorded well with analytical solutions and physical experiment values when L =0.6b1/2. In case of κ-ε model, experiment was conducted with values of Cμ known as physical models, but results were unsatisfactory. RNG κ-ε model showed best results for correlation coefficient, maximum velocity difference and drag coefficient when Cμ = 6 Cμ,0, which was similar to the results of experiment on wakes in sphere back by Rodi (1972). Accordingly, wakes were relatively well materialized when value of Cμ was about 6 times that of various existing flows. In the jet experiment with FLOW-3D, κ-ε model showed best results for correlation coefficient and maximum velocity difference when Cμ = 1.0 Cμ,0 Cε1 = 1.0 Cε1,0 and Cε2 = 1.0 Cε2,0. The values were mostly similar to experimental constants used in turbulence model of Launder and Spalding (1972). Accordingly, κ-ε model materialized jets using experimental constants proposed by Launder and Spalding (1972) with relative accuracy. RNG κ-ε model showed best results for correlation coefficient and maximum velocity with Cμ = 1.0 Cμ,0, Cε1 = 1.0 Cε1,0 and Cε2 = 1.0 Cε2,0, which are experimental constants used as basic index in the turbulence model of Yakhot et al. (1992). Accordingly, RNG κ-ε model showed relatively sound materialization using existing experimental constants.
Design of a tangential vortex drop structure using FLOW-3D
Ryan Edison, AECOM
AECOM recently completed the design of the Deep Rock Tunnel Connector (DRTC), which is an 18-foot diameter Combined Sewage Overflow (CSO) tunnel currently under construction in the City of Indianapolis as part of its Long-Term Control Plan (LTCP). The tunnel is approximately 43,000 lineal feet with depths ranging from 200 to 250 feet below grade. Along its route there are 3 CSO sites that required drop structures. The largest of these is CSO 008, which has a maximum operational design inflow of 300 MGD. It is this drop structure that was subjected to a detailed hydraulic design using FLOW-3D. This FLOW-3D based design was then validated at an independent physical laboratory. Using FLOW-3D as the central aspect in design proved vital to the management of both risk and timing for this large project, which is under an Environmental Protection Agency (EPA) consent order to be online by 2017. By the time physical modeling was underway, a high degree of confidence was needed so that there would be no design surprises – just validation. Upon the completion of physical modeling, the laboratory concluded that the FLOW-3D based design required no modifications. This finding was unique for the laboratory, which has tested numerous tangential vortex drop structures, and provides a strong example of the usefulness of FLOW-3D based designs to manage design risks, schedules, and costs. The findings of this study have since influenced the way that drop structures are designed and has solidified the use of FLOW-3D in such designs. This paper presents the FLOW-3D based design approach, results, and comparison to physical modeling measurements. Also, this paper presents how the standard H4-type design based upon the Milwaukee Inline Storage Project has stability problems under certain flow conditions and how FLOW-3D was used to identify these problems and find solutions. This was a central point in developing a working design. It is this point that is likely the reason why many initial designs of tangential vortex drop structures tested in laboratories require design modifications.
Evaluating high head ratios for labyrinth weirs
Bruce Savage1, Brian Crookston2, Greg Paxson3
1Dept. of Civil Engineering, Idaho State University
2Schnabel Engineering and Dept. of Civil and Environ. Engineering, Utah State University
A labyrinth weir is a passive control structure that is being implemented more frequently to increase flow capacity (e.g., spillway rehabilitation, replacement, new spillways) and regulate upstream water elevations (e.g., limited freeboard, flooding and water level control). A labyrinth weir is sharp-crested linear weir that is folded in plan-view in a W shape. Folding the weir increases the crest length, thereby increasing the discharge capacity relative to linear overflow control structures for a given channel width and upstream head. Prior published hydraulic design methods for labyrinth weirs are limited by their geometric and hydraulic design constraints; a function of the experimental data used to define the design methods. As a result, designers have been limited to headwater ratios (HT/P) below 1.0. This study presents the results and conclusions from physical and numerical (FLOW-3D) modelling of labyrinth weirs for headwater ratios exceeding 1.0 and a cycle width ratio (W/P) equal to 2.0. The configurations of both models are discussed with additional variations outlined in the numerical model. A comparison between the methods shows excellent agreement for the expected flow rate with a slightly larger discrepancy with the water surface elevations. The results of both methods expand the design parameters for labyrinth weirs.
Hydraulic modeling of whitewater kayak parks using FLOW-3D
Nell Kolden, Brian Fox; Colorado State University
Engineered whitewater kayak parks are becoming a popular amenity in many US cities. These parks include drop structures and flow constrictions, built in existing streams to create stationary hydraulic jumps for kayak recreation. The hydraulic characteristics created by these structures are often quite different from what would be found in an analogous natural stream. Various wildlife management agencies have raised concerns that these altered hydraulics could have negative effects on habitat, but little data has been collected to adequately describe or quantify the hydraulic differences. To better understand the specifics of hydraulic alteration, we used FLOW-3D to model six 100-ft reaches in the St. Vrain River in Colorado. Three of the reaches included a kayak drop structure, and the other three included a natural riffle/pool sequence. Due to the difficulty of collecting accurate hydraulic field data in these reaches, we determined that modeling would produce the most accurate description of channel hydraulics. Topographic surveys performed with GPS, Total Station, and ground-based LIDAR were stitched together using GeoMagic, which resulted in a highly accurate representation of bed topography. We collected model validation data for each reach at high and low flows, including discharge, water surface elevation profiles, point velocities, hydraulic jump heights, and eddy locations. Modeling results accurately depicted the complex three-dimensional flow found in deep pools below the engineered structures. A comparison of the natural and man-made structures at ecologically significant discharges showed higher velocities in the kayak parks and differences in flow patterns that could potentially influence the behavior and mobility of aquatic organisms.
Using numerical techniques for the prediction and management of the Russian River, CA
Fabián A. Bombardelli, 1 Shreya Hegde, 1 Kate Hewett, 1,2, Dane K. Behrens, 1,2 and John L. Largier2
1 University of California, Davis, 2 University of California, Davis, Bodega Marine Laboratory
There is an increasing acceptance of results of numerical simulations as adequate and useful tools to predict the flow in estuaries of the world, with the goal of managing those water resources. Numerical models can be used to explore diverse management scenarios through the development of multi-purpose objective functions, the analysis of hypothetical conditions, and the simplification of complicated scenarios. The Russian River estuary (RRE) characterizes by the closure of its mouth several times each summer, due to sediment deposition at the river mouth when the river flow rate is relatively low. During closure conditions, the circulation at the RRE changes dramatically: The exchange of salt with the ocean is suppressed, and water of high salt content becomes trapped below an approximately 1-m fresh water surface layer, generating stratification. The action of wind is responsible for internal seiches within the estuary. The strong stratification also precludes the transport of dissolved oxygen (DO) from the surface of the estuary to the deep waters. Because of bio-chemical processes in the water column, DO concentrations reduce near the river bed resulting in severe environmental problems. Aimed at addressing potential solutions for this complicated environmental conditions, two-dimensional simulations of the RRE with FLOW-3D have been developed. We simulated the flow in the RRE subjected to diverse river discharge and wind forcings, as well as for different management scenarios of the river mouth. Model results show a good quantitative agreement with the density contours obtained from field work, and an overall adequate prediction of the dynamics of the RRE in terms of seiches, thickness of the fresh-water layer, and response times.