Download user presentations that focus on applications of FLOW-3D for the aerospace industry from past users conferences.
Predicting phase change in cryogenic tanks during sloshing with CFD
Philipp Behruzi, ArianeGroup GmbH
Predicting boil-off rates in cryogenic tanks is of utmost importance in the space industry. Cryogenic fluids in rocket tanks may experience severe sloshing, impacting phase change. A reliable prediction of mass transfer with CFD is still to be resolved. Strong efforts are therefore spent on finding adequate phase change models to predict boil-off rates with Computational Fluid Dynamics (CFD). In this context, there has been quite a lot of activity at ArianeGroup over the past 10 years. Many experiments have been carried out which are today the basis for CFD tool development. In parallel, a number of CFD models exist or have been developed. The main physical problem is the need of refinement on the order of 0.1mm in the vicinity of the phase boundary, which is required to track the phase change physics correctly. Doing so on the scale of a launcher tank clearly states the problem. This presentation provides information on the current experimental and numerical status on this topic. A novel phase change model is introduced, based on a semi-empirical Nusselt number approach which is implemented into FLOW-3D. This model uses ideas provided by Ludwig et al. . The presentation will first outline the phase change model. Comparisons between experimental and numerical results are discussed, showing the validation status of the model. Furthermore, an outline concerning follow-up steps is given.
 Ludwig, C., Dreyer, M. E., and Hopfinger, E. J., “Pressure variations in a cryogenic liquid storage tank subjected to periodic excitations,” Int. J. of Heat and Mass Transfer 66, 223-234, 2013.
Modelling of upper stage cold gas reaction control propulsion systems
Francesco De Rose, ArianeGroup GmbH
Sloshing motions may imply large sloshing amplitudes in a ballistic environment. The coupling between the fluid and the rigid body motion is therefore very strong. Considering that future spacecraft use cryogenic liquids, there is also a strong emphasis on the thermal conditions in the tanks being influenced by propellant sloshing. Sloshing motions may lead to large tank pressure variations. Pressure variations will in turn affect the vented gas thrust often used in cold gas reaction control systems (RCS). An adequate modelling tool which can deal with these complex phenomena requires the following:
- Closed-loop coupling between rigid body motion and the impact of liquid sloshing, including the flight controller
- Coupling between the thermal behavior of the tank structure, the bulk liquid and the vapor
- Consideration of the propulsion system, especially when using cold gas systems. The RCS thrust level depends on the tank pressure and the condition at the propulsion line inlet, i.e., gas or liquid state
- Modelling of the cold gas nozzles, taking into account both gas and liquid expulsion
A precise prediction of the spacecraft’s behavior is essential for good launcher design and mission preparation. Therefore, analysis tools are required which can represent highly sophisticated real-world models of a space vehicle. To tie in with past developments, the software was recently coupled with a propulsion model for the cold gas RCS. This presentation delivers insight into the ArianeGroup closed-loop CFD analysis tool “FiPS” (Final Phase Simulator). An overview of the tool structure and the modelling of the relevant physical effects (sloshing behavior, pressure evolution, pressure losses in pipes and nozzle activations) is given.
Extension of FLOW-3D with a New Phase Change Model to Simulate Cryogenic Tank Flows
Martin Konopka, ArianeGroup GmbH
Cryogenic liquid propelled rockets are equipped with tanks containing subcooled liquid propellants such as hydrogen and methane. The pressure evolution in such tanks is governed by the heat exchange of the vapor with the tank walls and liquid surface, and the phase change at the liquid-vapor interface. Since phase change is a major driver for the pressure evolution, the accurate prediction of the phase change rate is of crucial importance for the design of cryogenic liquid tanks and their pressurization systems. Therefore, in this study FLOW-3D is extended with a customized phase change model based on the temperature gradients at the phase boundaries. To validate the customized phase change model, liquid evaporation at a heated wall, liquid evaporation at a superheated liquid body at a wall, the bubble growth problem in superheated liquid and meniscus evaporation in a heat pipe is considered. The numerical solutions of all computations show a good agreement with reference solutions. Furthermore, the phase change model is applied to the micro-gravity tank flow problem SOURCE-2 where HFE-7000 evaporates at a superheated wall. With the new phase change model, FLOW-3D can predict the pressure evolution with a maximum deviation of 0 % to 20 % compared with measurements.
Modelling of upper stage dynamics including fuel sloshing
Francesco De Rose, Airbus Safran Launchers
Launcher upper stages are supposed to carry out long ballistic flight phases. This comprises complex rigid body motions and multiple engine restarts, which can potentially lead to strong sloshing motions. Sloshing propellants act as a disturbance to the spacecraft’s motion. Accordingly, the more intense and abrupt the spacecraft’s manoeuvres are, the stronger the propellant sloshing is and the bigger the resulting disturbance back on the spacecraft is. An adequate modelling tool, which is able to deal with these complex problems, therefore requires the following feature:
- Closed loop coupling between rigid body motion and liquid sloshing including the flight controller
The focus concerning the FLOW-3D user conference is to provide insight into application aspects and quality of simulation results. In the introduction, a general description of the simulator structure will be given. Subsequently, an overview about the inclusion of the FLOW-3D software code into the Simulator FiPS® will be presented. The tool capabilities will be presented by means of closed loop CFD simulations of different ballistic flight phases. The mutual influence of vehicle and propellant motion during these modes and manoeuvres will be discussed.
Surface reorientation of liquid parahydrogen in microgravity
Peter S. Friese, University of Bremen, Center of Applied Space Technology and Microgravity
The reorientation of liquid parahydrogen (P = 0.95 Pa, T = 20.06K) in a cylindrical container due to a gravity step from normal to microgravity has been investigated experimentally at the drop tower Bremen. This experiment is modelled with FLOW-3D v11.0.2 and v11.0.4 as a one- and two-fluid simulation with the compressible gas model enabled. Though there is only a static contact angle model implemented in FLOW-3D, the one-phase simulation produces good results of the free-surface motion that agrees with the experimental data. The results of the two-fluid simulation differs from the experimental data not only in the thermodynamic but also in the fluid motion behavior. In v11.0.2, the steady state contact angle of the results does not agree with the ideal wetting condition in the setup. With the improvements in v11.0.4, the contact angle and the shape of the meniscus is calculated correctly. Irrespective of the version the solver does not compute the correct fluid motion in the two-fluid model, which appears unphysically damped.
Liquid sloshing simulations for space applications
Martin Siegl, Nicolas Darkow, and Dr. Jens Gerstmann, DLR Institute of Space Systems, German Aerospace Center (DLR)
A thorough understanding of liquid sloshing is fundamental to several areas of space engineering, in particular the design of launcher and satellite propellant tanks. Comprehensive CFD analysis of liquid behavior in partially filled tanks can aid tank design processes, but requires models of a range of physical phenomena and the interaction amongst them: liquids of low viscosity and low surface tension (as found in the form of liquid Hydrogen and liquid Oxygen fuels), varying changes of acceleration and its direction (rocket stages in different flight/slew phases), evaporation and condensation due to thermal input, and the characteristics of the free surface and the wall contact line/angle. Building upon the comprehensive CFD model set offered by FLOW-3D, the talk reviews two generic cases of lateral and longitudinal sloshing, both with high relevance in the domain of cryogenic fuel tanks. Emphasis is put on comparison of simulation results with experimental data – partially obtained at the DLR Cryolab Bremen – and options for a step-wise validation of the mentioned physical models. In the first test case, liquid in a cylindrical container is subject to a steep reduction of gravity, inducing longitudinal sloshing, additionally influenced by thermal gradients in the container walls. In the second test case, lateral sloshing is excited in a cylindrical tank with a convex dome bottom. For both cases, the damping of the oscillatory motion (after the end of any excitation) is investigated and compared to experiment. Thermal effects are discussed, where applicable.
Numerical study of capillary transport between parallel perforated plates
Diana Gaulke and Michael E. Dreyer; Fluid Mechanics and Multiphase Flows, ZARM University Bremen
Under microgravity and in small dimensioned devices capillary forces are used to transport and position liquid. Experimental data is difficult to acquire within both environments. Therefore, CFD software packages are used to broaden the parameter range to show relations and build an empirical database to evaluate analytical solutions. For capillary transport in tubes, between plates and in open channels it has been shown that FLOW-3D gives reliable results. The main focus of the ongoing work is to analyze the influence of perforation properties on capillary transport between parallel perforated plates under micro gravity. Some selected experimental data has been used to validate numerical simulations with FLOW-3D. It turns out that the accuracy of results depends on the used VOF algorithm for this geometrical configuration. During this presentation the experimental setup and the main objects of research are shown. A numerical grid study dependent on VOF algorithm and the corresponding experimental data are presented. Further, the calculation time for different mesh sizes and the parallelization speed up are shown for an example.
Preliminary numerical simulation of a suborbital experiment to investigate the behavior of liquid and gaseous hydrogen under compensated gravity and non-isothermal boundary conditions
Sebastian Schmitt and Michael Dreyer; Center of Applied Space Technology and Microgravity
Future cryogenic upper stages require a safe storage of the propellant for several hours during the different launch phases. The coasting where no accelerating forces are present is a crucial part during the launch campaign. Since there is little information about the behavior of liquid hydrogen in the absence of gravity a suborbital flight experiment with liquid hydrogen and non-isothermal boundary condition is under development at ZARM. The purpose of the experiment is to create a hydrogen gas bubble and investigate it in a microgravity environment. FLOW-3D is used to predict the behavior of a growing and contracting vapor bubble in subcooled hydrogen inside the test chamber. The purpose is to determine if the experiment design is sufficient enough to yield the desired results. A heater with an unsteady power input is used to control the phase change. Secondary heat sources, the thermal characteristic of the structure and temperature dependent material properties make an analytical investigation impractical. A possible experiment setup consists of a quadratic box with a window at the front and back side. The side walls are chosen much smaller than the front to model a pseudo 2D environment. One wall is attached to the LH2 tank to establish a fixed thermal boundary condition. The location of the heater is on the opposite side of the chamber and insulated from the aluminum.
Sloshing model and CFD analysis for the Euclid Mission
M. Lazzarin, A. Bettella, M. Manente; Hit09, M. Biolo; Weir Gabbioneta, R. Da Forno; MDA srl-MultiPhysicsLab and D. Pavarin; University of Padova
A theoretical model analyzing low-gravity sloshing in EUCLID reservoirs is presented. Model output is compared with CFD results for forces and moments on the tank walls. EUCLID is an observation satellite acquiring information from the deep space, by means of an optical technology. The continuous mission pointing movements induce propellant sloshing. This generates disturbances to the system stability. The aim of this study is to verify if the EUCLID reservoir configuration can maintain the satellite pointing within a maximum rotational angle of 20 milliseconds of arc, even when sloshing accelerations disturb the system. The developed model is derived from the basic equations of force and momentum balance. It is independent of the tank shape and based on lumped parameters. Non-linear effects have been neglected because of the low accelerations investigated. The tank is provided with a bladder, which required a capability to properly model a rubber-like material in CFD. The theoretical model has been verified with CFD analyses of two bladder-tank configurations: one filled at 22%, and another at 50%. Both fill levels have been studied applying two different bang-bang acceleration profiles. This CFD approach has been validated using literature for bladdered tanks subjected to known acceleration profiles. The difference between experiments and CFD is always lower than 25%, for the interesting parameters. The analytical model has been calibrated: lumped parameters have been found using CFD to replicate experiments. Tank response to sloshing has been reproduced using both the analytical model and CFD. The results obtained have been compared for consistency.
Using the FLOW-3D General Moving Object model to simulate coupled liquid slosh – container dynamics on the SPHERES slosh experiment aboard the international space station
Richard Schulman1, Sunil Chintalapati1, Hector Gutierrez1, Daniel Kirk1, Brandon Marsell2, Jacob Roth2, and Paul Schallhorn2
1Aerospace Systems and Propulsion Laboratory, Florida Institute of Technology, 2NASA John F. Kennedy Space Center
The SPHERES Slosh Experiment (SSE) is a free floating experimental platform developed for the acquisition of long duration liquid slosh data aboard the International Space Station (ISS). The data sets collected will be used to benchmark numerical models to aid in the design of rocket and spacecraft propulsion systems. Utilizing two SPHERES Satellites, the experiment will be moved through different maneuvers designed to induce liquid slosh in the experiment’s internal tank. The SSE has a total of twenty-four thrusters to move the experiment. In order to design slosh generating maneuvers, a parametric study with three maneuvers types was conducted using the General Moving Object (GMO) model in FLOW-3D. The three types of maneuvers are a translation maneuver, a rotation maneuver and a combined rotation translation maneuver. The effectiveness of each maneuver to generate slosh is determined by the deviation of the experiment’s trajectory as compared to a dry mass trajectory. To fully capture the effect of liquid re-distribution on experiment trajectory, each thruster is modeled as an independent force point in the FLOW-3D simulation. This is accomplished by modifying the total number of independent forces in the GMO model from the standard five to twenty-four. Results demonstrate that the most effective slosh generating maneuvers for all motions occurs when SSE thrusters are producing the highest changes in SSE acceleration. The results also demonstrate that several centimeters of trajectory deviation between the dry and slosh cases occur during the maneuvers; while these deviations seem small, they are measurable by SSE instrumentation.