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URANS Approach for Open-Channel Bifurcation Flows Modelling

URANS Approach for Open-Channel Bifurcation Flows Modelling. Adrien Momplot , Gislain Lipeme Kouyi , Emmanuel Mignot , Nicolas Rivière and Jean-Luc Bertrand- Krajewski Friday the 30 th of August - Sheffield. OUTLINE. Motivations/Background Objectives Material and Methods Results

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URANS Approach for Open-Channel Bifurcation Flows Modelling

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  1. URANSApproach for Open-ChannelBifurcationFlowsModelling AdrienMomplot, GislainLipemeKouyi, Emmanuel Mignot, Nicolas Rivière and Jean-Luc Bertrand-Krajewski Friday the 30th of August - Sheffield

  2. OUTLINE • Motivations/Background • Objectives • Material and Methods • Results • Conclusions SPN7 - Session: Monitoring and New Technologies Momplot et al.

  3. MOTIVATIONS • Singularities are often encountered in sewers (junctions, bifurcations, CSOs, etc.) and exhibit: • 3D pattern not understood with 1D or 2D modelling • High turbulence • Complex mixing processes and complex pollutant transport • European Water Framework directive imposes monitoring of quality and quantity of conveyed water • What about monitoring of dividing flows ? SPN7 - Session: Monitoring and New Technologies Momplot et al.

  4. MOTIVATIONS • Bifurcations instrumentation ? • Discharge repartition process in downstream branches • Contaminants transport/monitoring through the bifurcation SPN7 - Session: Monitoring and New Technologies moundsvillewwtp.com Neary and Sotiroupolous (1996)

  5. MOTIVATIONS • 3D CFD modelling based on RANS equations to understand complex 3D flows • However strong dependence on: • Parameters (mesh, boundary conditions) • Numerical options (turbulence models, wall functions, discretization schemes, etc.) SPN7 - Session: Monitoring and New Technologies Momplot et al.

  6. OBJECTIVES • Capability of RANS approach to reproduce bifurcation flow - particularly the discharge distribution in downstream branches • Improvements obtained with URANS approach SPN7 - Session: Monitoring and New Technologies Momplot et al.

  7. MATERIAL AND METHODS • Experiments performed in the channel intersection facility at the LMFA (Laboratoire de Mécanique des Fluides et d’Acoustique, INSA – LYON) SPN7 - Session: Monitoring and New Technologies Momplot et al.

  8. MATERIAL AND METHODS • Different flows investigated • PIV measurements at two elevations (z = 30 mm and z = 90 mm) • Discharge measurements in the lateral downstream branch SPN7 - Session: Monitoring and New Technologies Momplot et al.

  9. MATERIAL AND METHODS • Methodology: • RANS approach validation based on PIV measurements • Verification of the discharge distribution using the validated RANS model • Check the URANS improvements SPN7 - Session: Monitoring and New Technologies Momplot et al.

  10. MATERIAL AND METHODS • Optimum mesh is obtained when no significant improvements are observed with further refinements • Cell size Δx*Δy*Δz = 1mm*1mm*5mm in downstream branches SPN7 - Session: Monitoring and New Technologies Momplot et al.

  11. RESULTS Comparison between experimental data (PIV measurement) and simulations, using different turbulence model (RSM, k-ε RNG and k-ε standard) SPN7 - Session: Monitoring and New Technologies Momplot et al.

  12. RESULTS Model setup • Turbulence model: RSM • Wall function: scalable • Free surface representation: VOF model • Boundary conditions: mass-flow inlet for inlet, pressure outlet for outlets • Spatial discretisation scheme: Body-Force Weighted for pressure and Second-Order Upwind for other variables SPN7 - Session: Monitoring and New Technologies Momplot et al.

  13. RESULTS Discharge distribution: • RANS - steady state simulations give poor quantitative results for Case 1 (most quantitative studies have 10% as a maximum value for relative error) • Case 2 and 3 representations are better SPN7 - Session: Monitoring and New Technologies Momplot et al.

  14. RESULTS • URANS calculations are performed for Case 2, using the steady solution as an initial state SPN7 - Session: Monitoring and New Technologies Momplot et al.

  15. CONCLUSIONS • RANS method is able to reproduce the horizontal velocity • Some trouble to well represent the discharge distribution in downstream branches • URANS approach improves greatly the results, but with high computational cost ! • URANS approach or RANS approach (if relative error of 16% is acceptable) may help for bifurcation sites monitoring • using for e.g only one flow sensor in the upstream branch? SPN7 - Session: Monitoring and New Technologies Momplot et al.

  16. Thank you for your attention

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