IAHR 2015 - CFD simulations of a bubble screen, OMahoney, Deltares, 02072015
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CFD simulations of a bubble screen
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IAHR 2015 - CFD simulations of a bubble screen, OMahoney, Deltares, 02072015
- 1. 9 juli 2015 CFD simulations of a bubble screen Tom O’Mahoney Mike van Meerkerk
- 2. Contents of the talk • What is a bubble screen? • What do we eventually want to model? • What is known from literature on bubble modelling in CFD • Model setup • Lab scale simulations • Field scale simulation • Conclusions 9 juli 2015
- 3. What is a bubble screen? 9 juli 2015
- 4. What is a bubble screen? 9 juli 2015 Air mass flow Throughput of salt Value of 100 corresponds to the case without bubble screen
- 5. What is a bubble screen? 9 juli 2015
- 6. What is a bubble screen? 9 juli 2015
- 7. What is a bubble screen? 9 juli 2015
- 8. What is known from literature • Modelling of bubbles is a complex process • Within literature there is no consensus about which physical effects to model (depends on application) • Large scale measurements of bubble screens is sparse • Available data may not be satisfactory to validate a CFD model Main problems identified in the literature (on bubble columns) • The overestimation of turbulent viscosity, limiting the transient character of the flow • The missing 3rd dimension resulting in a higher generation of turbulent kinetic energy 9 juli 2015
- 9. Model setup • The Euler-Euler approach for multiphase flows is used because volume fraction of air is large but the bubbles small • Drag is the only interphase force of importance • Limitations on the CFL number and mesh size • RANS model used for turbulence 9 juli 2015
- 10. Lab scale simulations • Based on simulations by Wen and Forrest (1987) • Approximately 1m deep • Different flow rates • Velocity profile measured at different air flow rates 9 juli 2015
- 11. Lab scale simulations 9 juli 2015
- 12. Lab scale simulations 9 juli 2015
- 13. Lab scale simulations 9 juli 2015
- 14. Field scale simulation • Field scale tests, 10 times the depth of the lab scale experiments • Mesh is scaled accordingly but the bubbles are not scaled • Fewer air mass flow rates measured • Different limits of the viscosity ratio tested. Finally no limit given 9 juli 2015
- 15. Conclusions and future work • At lab scale 3D simulations are necessary but this could be due to the side wall effects • Those effects seem smaller at field scale so 2D may still be reasonable there • High turbulent viscosity ratios make the application of RANS modelling questionable • Available validation data is only without salt • The addition of the lock exchange flow is a work in progress 9 juli 2015