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boundary conditions for simpleFoam calculation |
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February 19, 2010, 03:49 |
boundary conditions for simpleFoam calculation
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#1 |
New Member
Patrick Wang
Join Date: Dec 2009
Location: Stuttgart, Germany
Posts: 26
Rep Power: 16 |
Hello everyone,
I am currently simulating the airflow over a car. I know what the results should look like, but after changing the boundary condition numerous times I am still unable to get realistic results (tried with both kepsilon model and komega model). I posted a picture of my simulation below (blended out some walls) as well as added the boundary conditions. fvSchemes and fvSolution were taken from either the motorbike tutorial (for k omega model) or pitzDaily tutorial (k epsilon model). I am calculating with simpleFoam. R, omega and k were also taken from these tutorials. Appreciate the help . Patrick P.S Which model (k epsilon / k omega model) is better for this calculation? epsilon: Code:
dimensions [0 2 -3 0 0 0 0]; internalField uniform 14.855; boundaryField { “car_.*” { type epsilonWallFunction; value uniform 14.855; } road_noslip { type epsilonWallFunction; value uniform 14.855; } symmetry { type symmetryPlane; } topwall { type slip; } sidewall { type slip; } inlet { type fixedValue; value uniform 14.855; } outlet { type zeroGradient; } roadslip { type slip; } } Code:
dimensions [0 2 -1 0 0 0 0]; internalField uniform 0; boundaryField { “car_.*” { type nutWallFunction; value uniform 0; } road_noslip { type nutWallFunction; value uniform 0; } symmetry { type symmetryPlane; } topwall { type calculated; value uniform 0; } sidewall { type calculated; value uniform 0; } inlet { type calculated; value uniform 0; } outlet { type calculated; value uniform 0; } roadslip { type calculated; value uniform 0; } } Code:
dimensions [0 2 -2 0 0 0 0]; internalField uniform 0; boundaryField { “car_.*” { type zeroGradient; } road_noslip { type zeroGradient; } symmetry { type symmetryPlane; } topwall { type slip; } sidewall { type slip; } inlet { type zeroGradient; } outlet { type fixedValue; value uniform 0; } roadslip { type slip; } } Code:
dimensions [0 1 -1 0 0 0 0]; internalField uniform (27.77 0 0); boundaryField { “car_.*” { type fixedValue; value uniform (0 0 0); } road_noslip { type fixedValue; value uniform (0 0 0); } symmetry { type symmetryPlane; } topwall { type slip; } sidewall { type slip; } inlet { type fixedValue; value uniform (27.77 0 0); } outlet { type zeroGradient; } roadslip { type slip; } } Code:
dimensions [0 2 -2 0 0 0 0]; internalField uniform 0.24; boundaryField { “car_.*” { type kqRWallFunction; value uniform 0.24; } road_noslip { type kqRWallFunction; value uniform 0.24; } symmetry { type symmetryPlane; } topwall { type slip; } sidewall { type slip; } inlet { type fixedValue; value uniform 0.24; } outlet { type inletOutlet; inletValue uniform 0.24; value uniform 0.24; } roadslip { type slip; } } Code:
dimensions [0 0 -1 0 0 0 0]; internalField uniform 1.78; boundaryField { “car_.*” { type omegaWallFunction; value uniform 1.78; } road_noslip { type omegaWallFunction; value uniform 1.78; } symmetry { type symmetryPlane; } topwall { type slip; } sidewall { type slip; } inlet { type fixedValue; value uniform 1.78; } outlet { type fixedValue; value uniform 1.78; } roadslip { type slip; } } Code:
dimensions [0 2 -2 0 0 0 0]; internalField uniform (0 0 0 0 0 0); boundaryField { “car_.*” { type zeroGradient; } road_noslip { type zeroGradient; } symmetry { type symmetryPlane; } topwall { type slip; } sidewall { type slip; } inlet { type fixedValue; value uniform (0 0 0 0 0 0); } outlet { type zeroGradient; } roadslip { type slip; } } |
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February 26, 2010, 02:03 |
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#2 |
New Member
Patrick Wang
Join Date: Dec 2009
Location: Stuttgart, Germany
Posts: 26
Rep Power: 16 |
problem solved
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March 2, 2010, 04:04 |
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#3 |
Member
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Do you like your drag results?
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March 2, 2010, 07:03 |
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#4 |
New Member
Patrick Wang
Join Date: Dec 2009
Location: Stuttgart, Germany
Posts: 26
Rep Power: 16 |
I haven't had the chance to implement liftDrag from OF 1.2. I have to do that when I have time. If you know a different way to calculate the drag coefficient with OF please share .
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March 2, 2010, 14:37 |
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#5 |
Member
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functions
{ forces { type forces; functionObjectLibs ("libforces.so"); outputControl timeStep; outputInterval 1; patches (OBJECT_OBJECT); pName p; Uname U; log true; rhoName rhoInf; rhoInf 1.17; magUInf 0.0045; CofR (1.25 0 4); } forceCoeffs { type forceCoeffs; functionObjectLibs ("libforces.so"); outputControl timeStep; outputInterval 1; patches (OBJECT_OBJECT); pName p; Uname U; log true; rhoName rhoInf; rhoInf 1.17; magUInf 0.0045; CofR (1.25 0 4); liftDir (0.0 1.0 0.0); dragDir (1.0 0.0 0.0); pitchAxis (0 0 0); lRef 0.5; Aref 12.56; } I use something like this in my /system/controlDict file. You must alter for your case, but this is a start. I'm not sure in which version that a forces function object (vocabulary?) was introduced off-hand. Regards, Ben Racine |
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March 2, 2010, 14:50 |
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#6 |
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The following thread is the reference for the above statements.
http://www.cfd-online.com/Forums/ope...es-v1-6-a.html |
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March 3, 2010, 06:10 |
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#7 |
New Member
Patrick Wang
Join Date: Dec 2009
Location: Stuttgart, Germany
Posts: 26
Rep Power: 16 |
Hey Ben,
Thanks for the code. I tried it and it worked without any problems. I have a couple of question regarding this code. 1. Which patches should I use for my simulation? Do I use every patch that defines the vehicle (I split the car into multiple parts: wheels, windshields and so on)? 2. And what is lRef? How do I calculate it? 3. Do you know a method for calculating Aref? Appreciate the help Patrick Wang |
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March 3, 2010, 20:17 |
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#8 |
Member
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1. Which patches should I use for my simulation? Do I use every patch that defines the vehicle (I split the car into multiple parts: wheels, windshields and so on)? Yes
2. And what is lRef? How do I calculate it? I believe it's the the length-scale used for finding Re number. 3. Do you know a method for calculating Aref? Aref is probably best done by doing a 2D frontal area projection of your surface model in some CAD package... as I believe it's typical to use frontal area in vehicle aerodynamics when calculating drag coefficients. Hope this helps and someone can correct if I'm wrong anywhere. Ben |
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July 1, 2015, 08:07 |
baklanton
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#9 |
New Member
Anton
Join Date: Nov 2014
Posts: 2
Rep Power: 0 |
Hi Patrick,
I am also experiencing an issue which is similar to the one you explained in your first post. Could you please explain how you solved it? Thank you! |
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