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November 21, 2011, 13:45 |
Mass Flow Problem
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#1 |
New Member
Student_87
Join Date: Nov 2011
Posts: 6
Rep Power: 14 |
Good evening
I am creating mass in my model, and I get very high velocities in the air phase. Anybody that have an idea where the mistake/s could be? Geometry data: Length of model = 10m, width=1m, Inlet area and outlet area = 1.25m^2, height step =0,25m. The geometry is set to be 70% filled with water. Set-up: - Pressure-based, velocity formulation absolute, transient, gravity=-9.81 - VOF, implicit, open channel flow, implicit body force, - k-epsilon, relizable, standard wall functions - Primary phase = air (constant density) and secondary phase = water - Inlet boundary: Multiphase, free surface level -2.14,bottom level -3.015. Air, mass flow rate = 0.045 kg/s Water, mass flow rate = 87,5 kg/s - Outlet boundary: Outflow, flow rate weighting = 1 - Reference values: v=0.1m/s - Solution method: PISO Any help would be appreciated |
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November 22, 2011, 11:51 |
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#2 |
Member
Laurent B
Join Date: Jun 2009
Location: Lille, FRANCE
Posts: 70
Rep Power: 16 |
Hi,
What's about your residuals ? Did you achieve convergence ? |
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November 22, 2011, 14:07 |
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#3 | |
New Member
Student_87
Join Date: Nov 2011
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Quote:
Under relaxation factors was set up: Pressure = 0.3 Density = 1 Body Forces = 1 Momentum = 0.5 Volume Fraction = 0.5 Turbulent Kinetic Energy = 0.8 Turbulent Viscosity =1 Thank you for trying to help me |
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November 23, 2011, 03:08 |
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#4 |
Member
Laurent B
Join Date: Jun 2009
Location: Lille, FRANCE
Posts: 70
Rep Power: 16 |
You must obtain convergence before checking mass imbalance.
Try to iterate more until you obtain convergence |
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November 23, 2011, 03:44 |
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#5 |
New Member
Student_87
Join Date: Nov 2011
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Thanks. I will do some more iteration to try to get convergence, but do you think the under relaxation factors seems reasonable? Is it corect to set this up as a transient problem, or should it have been steady state?
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November 23, 2011, 03:57 |
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#6 |
Member
Laurent B
Join Date: Jun 2009
Location: Lille, FRANCE
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The choice between steady and transient depends on what you want to do, what's the aim of your work ? don't matter about under relaxation factors before you are not sure of what you want to do exactly...
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November 23, 2011, 07:48 |
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#7 |
New Member
Student_87
Join Date: Nov 2011
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I want to see the effect the step has on the flow pattern.
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November 23, 2011, 08:21 |
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#8 |
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Laurent B
Join Date: Jun 2009
Location: Lille, FRANCE
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try to use steady state formulation
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November 24, 2011, 01:13 |
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#9 |
Senior Member
Join Date: Mar 2009
Location: Indiana, US
Posts: 186
Rep Power: 17 |
If it's an open channel flow, the top wall of your model should have a pressure BC of atmosphere
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November 24, 2011, 03:54 |
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#10 |
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Student_87
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