URANS Approach for Open-Channel Bifurcation Flows Modelling
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Transcript of 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 30th of August - Sheffield
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OUTLINE Motivations/Background
Objectives
Material and Methods
Results
ConclusionsFriday the 30th of August - 10.40 am - 11.00 am - Sheffield
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Momplot et al.
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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 ?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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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
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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.)
Friday the 30th of August - 10.40 am - 11.00 am - Sheffield
SPN7 - Session: Monitoring and New Technologies
MOTIVATIONS
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Capability of RANS approach to reproduce bifurcation flow - particularly the discharge distribution in downstream branches
Improvements obtained with URANS approach
Friday the 30th of August - 10.40 am - 11.00 am - Sheffield
SPN7 - Session: Monitoring and New Technologies
OBJECTIVES
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MATERIAL AND METHODS Experiments performed in the channel
intersection facility at the LMFA (Laboratoire de Mécanique des Fluides et d’Acoustique, INSA – LYON)
Friday the 30th of August - 10.40 am - 11.00 am - Sheffield
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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
Friday the 30th of August - 10.40 am - 11.00 am - Sheffield
SPN7 - Session: Monitoring and New Technologies
Momplot et al.
PIV measurement flow Case 1 Case 2 Case 3Inlet discharge Q 4 L/s 4 L/s 4 L/s 4 L/s
Weir height in the main downstream branch 98.13 mm 34.50 mm 25.78 mm 18.41 mm
Weir height in the main lateral branch
98.14 mm 12.16 mm 22.19 mm 32.73 mm
Measured discharge in the lateral branch
Not measured 3.18 L/s 2.05 L/s 0.91 L/s
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MATERIAL AND METHODSMethodology:
RANS approach validation based on PIV measurements
Verification of the discharge distribution using the validated RANS model
Check the URANS improvements
Friday the 30th of August - 10.40 am - 11.00 am - Sheffield
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Optimum mesh is obtained when no significant improvements are observed with further refinements
Cell size Δx*Δy*Δz = 1mm*1mm*5mm in downstream branches
Friday the 30th of August - 10.40 am - 11.00 am - Sheffield
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MATERIAL AND METHODS
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RESULTS
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Comparison between experimental data (PIV measurement) and simulations, using different turbulence model (RSM, k-ε RNG and k-ε standard)
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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
Friday the 30th of August - 10.40 am - 11.00 am - Sheffield
SPN7 - Session: Monitoring and New Technologies
RESULTS
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RESULTSDischarge 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
Friday the 30th of August - 10.40 am - 11.00 am - Sheffield
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Case 1 Case 2 Case 3Measured Lateral discharge Q (L/s) 3.18 2.05 0.91Simulated Lateral discharge Q (L/s) 2.73 (-16%) 1.87 (-9%) 1.03 (+11%)
Difference between inlet and outlet (L/s) 0.09 (-2,3%) 0.10 (2.5%) 0.07 (1.75%)
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RESULTS URANS calculations are performed for Case 2,
using the steady solution as an initial state
Friday the 30th of August - 10.40 am - 11.00 am - Sheffield
SPN7 - Session: Monitoring and New Technologies
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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?
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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