Reconstruction and Extension of the Méricourt Locks: Study of Hydraulic Operations

FLOW-3D HYDRO Case Studies

Reconstruction and extension of the Méricourt locks: Study of hydraulic operations

This article was contributed by Gwenaël CHEVALLET, Chloé CHENE, Antoine HALBARDIER, and Franck RANGOGNIO, BRL ingenierie.

With more than 60 years of experience in large scale hydraulic infrastructures, BRL Ingénierie is a leading company in the navigation sector both in France and abroad.

Modeling Premise

The design of a lock and the associated lock management operations are complex problems that are typically addressed using:

  • Scaled physical models that can be laborious to implement.
  • Issue-specific empirical methods often coupled with calculation approaches.
  • 1D transient hydraulic studies to verify compliance with average velocity, water line slopes and locking times criteria.
  • 3D steady-state hydraulic models for the filling and emptying of valve elements.
  • Charts or simplified calculation approaches for mooring problems.
  • Feedback from operators.

The BRL ingénierie teams has implemented a methodology to address these modeling needs in a combined way using transient 3D CFD hydraulic analysis with the CFD software FLOW-3D.

Methodology

The renovation and extension project of the Méricourt locks on the Seine aims to rebuild the existing locks, as they present visible structural disorder, particularly through the deformation of the lock walls. The site currently holds two parallel functional locks, one with a 160m capacity lock chamber, and the other with a 185m capacity lock chamber. As part of the scope of the project, the owner (Voies Navigables de France, VNF), aimed to, among other objectives:

Mericourt locks aerial view
Figure 1. Aerial view of Méricourt locks. On far left is a decommissioned lock; next to it are Locks no. 1 (middle) and 2 (right).
  • Extend the 160m lock to standardize the capacity of the locks, thus securing the navigation axis. This extension will lead to an increase in the filling and emptying volumes.
  • Install floating bollards to replace the existing fixed bollards.
  • Replace the downstream valve parts (2 aqueducts replaced by 18 valves).

These changes come with a strong requirement from the owner to maintain locking times close to the current 15min locking time, and at the same time comply with maximum force limits on the bollards, 250 to 300kN per bollard (25 to 30 tons).

The model presented here is for lock no. 1 (L=185m, W=17m) and includes:

  • A 3D CAD lock geometry
  • A FLOW-3D transient 3D hydraulic model capable of simulating all the complexities of the flow (stationary flows, eddies, air entrainment, cavitation, water hammer, etc.)
  • Prescribed and coupled moving objects modeling in FLOW-3D
    • Coupled to the fluid:
      • A Grand Rhénan type boat (ECMT class Va, L=110 m, w =11,4 m, capacity 1500 to 3000 tons)
Grand Rhenan type boat geometry
      • Floating bollards
    • Prescribed motions of upstream aqueduct gates or downstream valves in accordance management instructions.
  • A mooring module linking the vessel to the bollards
  • A collision module between the boat and the lock walls
FLOW-3D model of lock no.1
Figure 2. FLOW-3D model of lock no.1 in project situation - Grand Rhénan
Lock no. 1 project simulation

Results

Once the boundary conditions were set (forebay and tailbay water levels) and the characteristics of the vessel and the mooring plan were chosen, the implemented model allowed for detailed evaluation of the following conditions:

  • Duration of a filling or emptying cycle for given management instructions.
  • 3D hydraulic conditions of the flows in the airlock (mainly velocity distribution).
  • Forces transmitted in the bollards during a filling or emptying cycle.
Lock no. 1 project simulation
Figure 5. Simulation of filling of lock n°1 – project situation (2 mooring lines) - Grand Rhénan

Based on simulation results, it was then possible to optimize the filling or emptying management instructions in order to:

  • Ensure compliance with the maximum forces in the bollards
  • Minimize the duration of the locking times (about 10 to 11 minutes) while respecting the material constraints of the valve components (range of operating speeds of the oil circuit pump in particular).
Optimized law of filling by aqueducts
Figure 7: Optimized law of filling by aqueducts
Optimized law of filling by aqueducts
Optimized law of filling by aqueducts

Conclusion

FLOW-3D made it possible to evaluate the design and optimization strategies related to locking (emptying/filling time, hydraulic loads, forces on the boat and forces on floating bollards, etc.) with a single tool. It is in fact a real step forward for the practice. Indeed, this methodology is applicable to all types of locks and all types of vessels.

The results of the modeling carried out so far are particularly satisfactory and are aligned with all order of magnitude calculations using charts, simplified methods or based on the operator’s feedback (emptying/filling laws, flow coefficients of the valves, maximum forces on the bollards, etc.).

Concerning the forces on the bollards (essential dimensioning parameters), the results are obviously tied to the filling schedules, the free length of the mooring lines and their rigidity, as well as to the general mooring plan (number and position of mooring lines), detailed parameters which are all included in the FLOW-3D model.

EREDOS PROJECT: Numerical Modeling of Flows in Covered Streams

FLOW-3D HYDRO Case Studies

EREDOS PROJECT: Numerical Modeling of Flows in Covered Streams

European fund of regional development
PROJECT CO-FINANCED BY THE EUROPEAN FUND OF REGIONAL DEVELOPMENT

This article was contributed by Gwenaël CHEVALLET, Marie-Christine GERMAIN, and Sarah LASNE, BRL ingenierie

With more than 60 years of experience in large-scale hydraulic infrastructure, BRL ingenierie is a key player in the field of water engineering both in France and abroad.

The mining industry has led to the construction of many underground structures to manage the exploited territories and to accompany their economic and industrial development. This activity has created voids and has been accompanied by the creation of slag heaps and the filling of valley bottoms with different materials, mainly waste rock. These fillings were preceded by masonry work above the watercourses to maintain the flow through the valley. They were later accompanied by other deposits of materials resulting from the creation of dwellings or infrastructure.

Since the decline of mining activity, these constructions have not received additional maintenance. The November 2012 collapse of a covered brook in Robiac-Rochessadoule (France, Gard) showed that it is important to pay renewed attention to these constructions that have been forgotten over time.

Collapse of covered stream
Figure 1. Collapse of the covered stream in Robiac-Rochessadoule in November 2012

The EREDOS research project, in which BRL ingenierie participates, has the following objectives:

  • To develop tools and methods for carrying out diagnostic studies (monitoring system, mechanical and hydraulic behavior, etc.) of these covered streams and the structures that cross them.
  • To define risk indicators and intervention protocols.

Within this research framework, BRLi tested the use of 3D CFD to address concerns related to the issues of covered streams. The CFD model was built using FLOW-3D software with the input of a detailed 3D scan of the covered stream (RICHER firm – Geometer-Expert).

3D Scan of the Tunnel

The Valette stream is located in the commune of Robiac-Rochessadoule, 20 km north of Alès in France. The masonry structure has a total length of approximately 250 m. The photos below are presented looking downstream and are taken from the film made with the help of the 3D scanner. The collection of high-resolution geometry data allowed for creating a highly accurate 3D CAD model to be used as input for the FLOW-3D simulations. 

Hydraulic Model

The main task was a parametric study based on a hydraulic 3D CFD model built with FLOW-3D software of the entire underground stream. The main parameters that were tested were:

  • Upstream and downstream boundary conditions
    • Upstream: imposition of flows or water levels
    • Downstream: free outflow or imposed water levels
  • Absolute roughness of the tunnels
  • Mesh size
  • Turbulence models (K-epsilon, K-omega, RNG)
  • Consideration of flow aeration phenomena (single fluid [water] + specific air model or two-fluid [water+air] model)
  • Numerical options (1st order, 2nd order…)
  • Law of walls

In total, more than 40 3D CFD simulations were carried out.

Hydraulic Results

Despite tests varying many parameters (sometimes in very wide ranges), the maximum calculated flows that can pass through the tunnel remain robustly confined to a range of 100-125 m3/s. The simulation results, for this specific premise and these spatial scales, appear not to be particularly sensitive to the parameter space variations explored by the modeler.

The maximum physical flow that can pass through the tunnel is estimated to be about 100 m³/s. By maximum physical flow, we mean a flow that generates an upstream level of about 8 to 9 m (model reference), compatible with the natural topography in the vicinity of the upstream entrances.

The upstream rating curve of the tunnel resulting from this approach was then inserted. In the flow range of 60-120 m³/s, a culvert law applied to the first tunnel with a flow coefficient of 0.6 aligns well with the rating curve obtained using FLOW-3D.

Hydraulic Stresses of Structures

This type of 3D CFD model offers the possibility of extracting from the results of the simulations many parameters related to the evaluation of hydraulic stresses on the structure: dynamic pressure, shear stresses, dissipated energy, etc.

These outputs make it possible to diagnose the current state of the structure stability and to design for a possible reinforcement. They constitute input data for the structural analysis of the structures.

In the flow regimes of concern, an alternation of pressurized and free surface flow conditions, it should be noted that it is possible to observe beating phenomena at the origin of depressions on the walls that can prove to be prejudicial.

The figures below illustrate the type of rendering that can reveal pressure solicitations on the hydraulic structures.

Energy dissipation hydraulic structure
Figure 12. Postprocessing of the results on the structures (dissipated energy)
Postprocessing results hydraulic structures
Figure 11. Postprocessing of the results on the structures (pressure)

Conclusion

High fidelity 3D scan data can be used as the foundation for sophisticated 3D CFD modeling of complex flow conditions using advanced modeling tools such as FLOW-3D. Discharge curves and detailed representations of the flow, with the resulting transient pressure conditions on the surrounding infrastructure are all part of the deliverables that naturally result from this kind of study.

Siphon Spillways

FLOW-3D HYDRO Case Studies

Siphon Spillways

This article was contributed by Ali Habibzadeh (Project Engineer) and Jose (Pepe) Vasquez (Principal Engineer) at Northwest Hydraulic Consultants.

CFD modeling is a powerful tool for evaluating the hydraulic design of spillway structures. The capacity of the spillway at design flow is of paramount significance in terms of dam safety (USBR 1987). Northwest Hydraulic Consultants has applied CFD modeling in numerous case studies of existing or new spillway designs. The following article demonstrates a sample case study conducted on an existing siphon spillway.

Air-regulated siphon spillways operate under different hydraulic conditions depending on the upstream water level (McBirney 1957). For relatively small heads over the crest of the spillway, the siphon operates like a free weir with atmospheric pressure inside the siphon barrel (i.e. discharge will be proportional to hw3/2). As the head increases, flow within the siphon barrel transitions to pressurized flow; the siphon barrel will be primed with sub-atmospheric pressure. At that stage, discharge through the siphon barrel is like that of an orifice (i.e. discharge will be proportional to ho1/2). The driving head through a primed siphon is equal to the differential head between the upstream water level and the water level just downstream of the siphon exit. Because the effective head on a primed siphon (ho) is, in general, significantly larger than the head over a free siphon (hw), the primed siphon can convey a significantly larger amount of flow when compared to a free siphon with a slight increase in the upstream water level (Ervine 1976). However, this is only true if the siphon actually primes (Tadayon and Ramamurthy, 2013). During floods and emergency events, it is extremely important that a siphon self-primes without human intervention, but this is not always what occurs.

To enhance priming, deflectors are often installed along the floor of siphons to generate a jet directed towards the opposite wall to enclose a confined volume of air. The increased turbulence generated by the jet gradually removes the confined air, dropping the pressure within the barrel.

As the upstream water level drops, the prime within the siphon breaks and flow switches back to atmospheric pressure. As this transition occurs, the discharge decreases significantly, with the head-discharge relation switching from an orifice to a weir.

Siphon spillways schematic
Schematic section view of siphon spillway; weir flow (left) and orifice flow (right).

FLOW-3D Modeling of a Siphon Spillway

Northwest Hydraulic Consultants used FLOW-3D to evaluate the discharge capacity of an existing 3-ft high rectangular siphon spillway. Since the existing siphon experienced issues with self-priming during floods, a hooded air vent at the entrance and a floor deflector within the barrel were added. The first animation below, shows a section model of the siphon with increasing upstream water level.

The first animation was conducted with a fixed upstream water level that was determined from field observation at the existing spillway. The deflection of the flow by the floor deflector results in a confined volume of air within the barrel. Over time, this air is entrained by the flow resulting in the absolute pressure within the barrel to drop from atmospheric (~2,115 lb/ft2) to sub-atmospheric (around 1,500 lb/ft2). As the pressure drops within the barrel, air is removed and replaced by water. The discharge through the siphon increases from less than 1 cfs to more the 16 cfs when the siphon is primed, and the barrel runs full.

The second animation illustrates the siphon prime break action as the upstream water surface elevation decreases. The process of siphon prime break occurs when the difference between the atmospheric ambient pressure and pressure at the crown of the siphon barrel exceeds the differential head required to entrain air into the siphon. Hence, the siphon prime breaks and air replaces fluid within the barrel. As shown in this animation, after the siphon prime break action is complete, inside pressure and discharge through the barrel return to their original weir flow values.

The results of FLOW-3D were confirmed by a physical model study conducted at Northwest Hydraulic Consultants’ hydraulics lab.  

References

Ervine, D. A., (1976). “The Design and Modelling of Air-Regulated Siphon Spillways.”, Proceedings of the Institution of Civil Engineers, Vol. 61, pp. 383-400.

McBirney, W. B. (1957). “Some Experiments with Emergency Siphon Spillways.”, US Bureau of Reclamation, PAP-97.

Tadayon, R. and Ramamurthy, A. S., (2013). “Discharge Coefficient for Siphon Spillways.”, ASCE Journal of Irrigation and Drainage Engineering, Vol. 139, No. 3, pp. 267-270.

USBR. (1987). “Design of Small Dams.”, 3rd Ed., U.S. Government Printing Office, Washington, DC.

Hydraulic Jump in a Trench Type Pump Sump

FLOW-3D HYDRO Case Studies

Hydraulic Jump in a Trench Type Pump Sump

This article was contributed by Steve Saunders, Principal at the Ibis Group

Hydraulic jumps are a flow phenomenon familiar to people working with open channel applications. Wikipedia defines a hydraulic jump as “a condition where open channel flow abruptly transforms from super- to sub-critical.” At the location where the jump occurs, one can observe velocity head getting traded for a step-up in water surface elevation. In flow control applications like spillways, hydraulic jumps are set up intentionally as a means of dissipating energy to mitigate erosion. They also come into play for recreational purposes. The standing waves created by hydraulic jumps are used to train surfers how to ride in surf parks that can be thousands of miles from any ocean. A novel application for hydraulic jumps is in self-cleaning trench type pump sumps where the energy transfer of the jump resuspends and carries away solids that have settled out during normal pumping operations.

Simulating a Trench Type Sump Pump

FLOW-3D has proven to be a reliable tool in simulating hydraulic jumps and has been put to use in the design and demonstration of a self-cleaning trench type pump sump. The trench type pump sump comprises a narrow channel with a line of pump intakes. A typical application is storm water collection where no inlet screens are present to strain out grit and gravel from the incoming water. An example is presented in the schematic below.

This figure is taken from the ANSI/HI 9.8 Pump Intake Design manual and shows plan and elevation views of a sump with four pumps installed. The arrangement of the inflow culvert, sump floor and pump suction off-floor elevations is critical to the self-cleaning capability of this design type. Take note that the inflow culvert is at an elevation higher than the minimum operating sump water level. Also, the trench wall at the inflow end has an ogee shape. Finally, the pump intake bell at the far (right) end of the trench is set an elevation half of that of the upstream pumps.

Designing for Storm Events

After a storm event, grit and gravel settle on the sump floor. They get re-suspended and drawn off by means of a progressive hydraulic jump. During a cleaning cycle, the water is drawn off by the lower pump at the far end of the trench at a higher rate than is entering through the inflow culvert. As the water drops below the minimum normal operating level, the inflow accelerates down the ogee-shaped wall and ultimately becomes supercritical. Once the water level in the sump nears the floor, a hydraulic jump forms and progresses along the sump until the lower far end pump loses its suction. You can observe this taking place in the animation below.

During this sequence, the hydraulic jump performs two important roles. The supercritical portion upstream of the jump scours the sump floor of grit and gravel thereby re-suspending it to be pumped away. A glance at the color scale in the animation will tell you that the scour velocity at the base of the ogee nears about 9 ft/sec. Meanwhile, the stepped-up water elevation downstream of the jump provides the lower end pump with sufficient submergence to continue operating until the sump is pumped out.

The Magnolia Storm Water Pumping Station

Using FLOW-3D for this self-cleaning sump application means the trench geometry can be readily adjusted to optimize the action of the hydraulic jump. The Magnolia Storm Water Pumping Station in El Paso, Texas is an example where FLOW-3D was used as a design and evaluation tool. Commissioned in 2016, the Magnolia Storm Water Pumping Station was constructed to eliminate the flooding of Interstate 10  during heavy rain events. The Magnolia station comprises three large vertical turbine pumps in a self-cleaning trench type sump. During the sump design process, several geometry variations were evaluated with FLOW-3D thus arriving at a configuration ideal for pump operational efficiency and ease of maintenance by way of its self-cleaning capability.

Mitigating Total Dissolved Gas at Boundary Dam

FLOW-3D HYDRO Case Studies

Mitigating Total Dissolved Gas at Boundary Dam

This article was contributed by Nikou Jalayeri, Water Resources Engineer at 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 (Spillway 1 and Spillway 2), and an approximately 1,003 MW authorized capacity powerhouse. The spillway and sluiceway discharge at the Boundary Hydroelectric Development have been shown to produce high total dissolved gas (TDG) concentrations in the tailwater of the spillway and 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. This model was also used to simulate the entry and movement of these flows through the project’s downstream plunge pool and powerhouse area.

FLOW-3D model spillway roughness elements
Figure 1. 3-D View of Spillway 1 Roughness Elements

FLOW-3D was selected for the analysis given its ability to simulate free falling jets, and its unique algorithm for simulating air entrainment by turbulence at the free surface. These capabilities make the program very well suited for simulating the varied and complex flow conditions in the project tailrace. The FLOW-3D models developed for the Boundary Dam study have primarily been used to develop an understanding of the governing hydraulic and hydrodynamic processes driving gas exchange in the tailrace of the existing project under spill conditions. In addition, these models been used to develop the designs of structural TDG mitigation alternatives (including estimation of the hydraulic loads expected on proposed appurtenances), and in combination with the TDG predictive model, to predict the TDG performance of proposed TDG mitigation alternatives.

Boundary Dam Hatch FLOW-3D
Figure 2. 3D View of the Unmodified Spillway 1 Jet: 10,000 cfs Flow (left), 13,000 cfs Flow (right)

To do so, representative air bubbles were released on the spillway in the model and tracked as they were entrained into the plunge pool and tailrace, circulated within the plunge pool, and eventually exhausted at the surface.  The model tracked the pressure- and time-histories associated with each of these representative air bubbles.  This data was 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.  TDG predictions were made for the project using a two-step process:  the CFD model was first applied to assess the plunge pool hydraulics and flow patterns, and then the hydraulic output of the CFD model was imported into the Plunge Pool Gas Transfer (PPGT) model, which was developed using Excel.

The model was first run to simulate flow conditions for the existing or base case scenario with flows of 10,000, 13,000, and 20,000 cfs through each of the Project Spillways. The simulated hydraulic conditions for this test were analyzed. Bubble particles were then added to this model, the run was re-started, and the particles were tracked until they were able to reach the surface, and exhaust back into the atmosphere.

Following the base case runs, various CFD simulations were conducted to assess the hydraulic conditions that would result from the introduction of Roughness Elements (REs) on the downstream end of the spillway chute.  The introduction of these REs helps to break up the jet at the end of the chute more quickly and efficiently, accelerating boundary layer growth and resulting in the formation of small “packets” of water entering the plunge pool rather than coherent streams/jets.  This accelerated breakup of the jet will help to reduce overall plunge depths, and reduce gas transfer. Given concerns for potential cavitation damage on the spillway chute floor and on the REs themselves, additional runs were undertaken to test the effect on flow conditions at the REs if a ramp were to be installed immediately upstream of the roughness elements. The Spillway 1 RE geometry is presented in Figure 1.

Modified spillway FLOW-3D design
Figure 3. 3D View of the Modified Spillway 1 Jet : 10,000 cfs Flow (left), 13,000 cfs Flow (right)

The final model results were used to help assess the impact that the addition of these modifications would have on TDG levels downstream of the project under a range of flows.  CFD runs were made with identical flow releases through the spillways under both existing and modified conditions, bubble histories were extracted from the CFD results and input to the TDG predictive spreadsheet model. The results showed that the proposed RE configuration for Spillway 1 is effective at reducing TDG production, but appears to deliver the greatest TDG reduction when operating at a flow of approximately 10,000 cfs. For higher flows, the ability of the roughness elements to break up the jet appears to be reduced, since the jet begins to override the roughness elements. This results in the formation of a more competent jet core that is able to penetrate the plunge pool to a greater depth. Figure 2 illustrates the difference between the baseline (existing) case and the modified Spillway 1 for flows of 10,000 cfs and 13,000 cfs respectively.

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