1. URANS A PPROACH FOR O PEN - C HANNEL B IFURCATION F LOWS M ODELLING Adrien Momplot, Gislain Lipeme Kouyi, Emmanuel Mignot, Nicolas Rivière and Jean-Luc Bertrand-Krajewski Friday the 30 th of August - Sheffield

2. OUTLINE Motivations/Background Objectives Material and Methods Results Conclusions Friday the 30th of August - 10.40 am - 11.00 am - Sheffield 2 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 ? 3 Friday the 30th of August - 10.40 am - 11.00 am - Sheffield SPN7 - Session: Monitoring and New Technologies Momplot et al.

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

5. 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.) 5 Friday the 30th of August - 10.40 am - 11.00 am - Sheffield SPN7 - Session: Monitoring and New Technologies MOTIVATIONS Momplot et al.

6. Capability of RANS approach to reproduce bifurcation flow - particularly the discharge distribution in downstream branches Improvements obtained with URANS approach 6 Friday the 30th of August - 10.40 am - 11.00 am - Sheffield SPN7 - Session: Monitoring and New Technologies OBJECTIVES 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) 7 Friday the 30th of August - 10.40 am - 11.00 am - Sheffield 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 8 Friday the 30th of August - 10.40 am - 11.00 am - Sheffield 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 9 Friday the 30th of August - 10.40 am - 11.00 am - Sheffield SPN7 - Session: Monitoring and New Technologies Momplot et al.

10. Optimum mesh is obtained when no significant improvements are observed with further refinements Cell size Δx*Δy*Δz = 1mm*1mm*5mm in downstream branches 10 Friday the 30th of August - 10.40 am - 11.00 am - Sheffield SPN7 - Session: Monitoring and New Technologies MATERIAL AND METHODS Momplot et al.

11. 11 RESULTS Momplot et al.Friday the 30th of August - 10.40 am - 11.00 am - Sheffield SPN7 - Session: Monitoring and New Technologies Comparison between experimental data (PIV measurement) and simulations, using different turbulence model (RSM, k-ε RNG and k-ε standard)

12. 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 12 Friday the 30th of August - 10.40 am - 11.00 am - Sheffield SPN7 - Session: Monitoring and New Technologies RESULTS 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 13 Friday the 30th of August - 10.40 am - 11.00 am - Sheffield 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 14 Friday the 30th of August - 10.40 am - 11.00 am - Sheffield 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? 15 Friday the 30th of August - 10.40 am - 11.00 am - Sheffield SPN7 - Session: Monitoring and New Technologies Momplot et al.

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