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kOmegaSST without turbulence modelling of the flow around geometry |
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December 5, 2013, 03:17 |
kOmegaSST without turbulence modelling of the flow around geometry
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#1 |
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Hello together,
I'm trying to simulate some kind of geometry in a wind tunnel with inlet, outlet and the walls of the wind tunnel. Laminar simulations are working fine but turbulence modelling doesn't the way I like to have it. I'm using a modified rhoCentralFoam-solver with mach 0.8. For turbulence modelling I use the kOmegaSST model. My mesh is a very fine one with about 30 boundary layers around my geometry(except the walls of the wind tunnel). As I said, laminar simulations work fine and Cdrag fits with my reference value. For k I use the following setting: Code:
dimensions [0 2 -2 0 0 0 0]; internalField uniform 2.78; boundaryField { wind tunnel wall { type slip; } inlet { type turbulentIntensityKineticEnergyInlet; intensity 0.005; value uniform 2.78; } outlet { type inletOutlet; inletValue uniform 2.78; value uniform 2.78; } geometry { type compressible::kqRWallFunction; value uniform 2.78; } } Code:
dimensions [0 0 -1 0 0 0 0]; internalField uniform 55.57; boundaryField { wind tunnel wall { type slip; } inlet { type fixedValue; value uniform 55.57; } outlet { type inletOutlet; inletValue uniform 55.57; value uniform 55.57; } geometry { type compressible::omegaWallFunction; value uniform 55.57; } } Running this simulation i get a much higher Cdrag value as my reference value. I think the problem is the turbulence modelling at inlet and outlet. I only want to use the compressible wall function for my geometry and no turbulence modelling of the freestream around my geometry. I've also tried some other boudary conditions at in- and outlet but most of them doesn't work. How can I solve this problem? Does anybody understand my problem and has some ideas? If there are any questions left, please reply and I will answer. Best regards, CFDnewbie147 |
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December 5, 2013, 05:35 |
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#2 |
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Philipp
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Do you resolve the boundary layer (y+=1) ?
If so, you need to set k to some low value instead of using a wall function. Maybe that is the problem.
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December 5, 2013, 05:44 |
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#3 |
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Hello Philipp,
thank you for answering. Yes I resolve the boundary layer. So the boundary conditions for inlet and outlet are ok and I "only" have to set a low number of k for the geometry instead of the wallfunction? Low number means about 0.1 or 1 or what do you propose? And what's about omega? How to set this value? Best regards, CFDnewbie147 |
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December 5, 2013, 05:53 |
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#4 |
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Philipp
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Hi,
I don't know if the inlet / outlet is fine, this depends on your case. But if you calculated these values by hand (!?) it should be ok. I only know about incompressible boundary conditions, I don't know if the compressible differ. But in the incompressible case, omegawallfunction needs to be used for low and high-Re cases. It automatically switches from y+=1 to wall modelling. I think this also will be done in your case. Normally k should be zero at the wall for your case, but it seems that some equation divides by "k", so it should not be zero. People in this forum usually use a very small number (such as 1e-12) for k which is effectively "0", but avoids the zero devision. Good luck. And post again if it works.
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December 5, 2013, 06:01 |
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#5 |
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Hello again,
but this options for inlet and outlet mean that there is a modelled turbulence in the flow around my geometry, but I don't want this. I only want to use the kOmegaSST-model for the geoemtry and its boundary layers. But I will try your suggestion. Thank you again. Best regards, CFDnewbie147 |
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December 5, 2013, 06:06 |
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#6 |
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Philipp
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If you choose a turbulence model this will be used in your whole geometry. This model needs boundary conditions also at your inlet and outlet. I don't understand your problem.
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December 5, 2013, 08:28 |
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#7 |
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Ok, you're right at all.
Do you know what kind of condition is used in the background of the simulation when setting the boundary condition of k / omega to "slip"? Best regards, CFDnewbie147 |
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December 5, 2013, 08:29 |
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#8 |
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Philipp
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No sorry. I never used "slip", I only use fixedValue or zeroGradient.
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