Problem in simulations

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Debashis Basu

Problem in simulations

Post by Debashis Basu »

Here is where I currently am and the issues I am working to resolve.  Any advice, correction, or conclusions are welcomed. 
 
Issue 1)
 
While working with turbulent channel flow problems I found out that the no slip wall condition was not present in my results (ie Velocity at wall was not zero).  This is my current problem which I am trying to resolve.  To investigate I scaled back to a pipe flow problem.  Running the simulation as laminar with a Reynolds number around 100 yields the expected results and velociy profiles for classical pipe flow.  However running the simulation as turbulent, Reynolds number of 30,000 using the K-epsilon turbulence model does not show zero velocity at the walls.  Reading about the K-epsilon turbulence model online I got the impression it may not be the best set of assumptions to use near the wall/boundary layer.  Is this correct? Indeed viewing my results showed the velocity gradent dv/dy near the wall was near infinite.  What turbulence model, might you recommend.
 
Issue 2)
 
I am trying to enforce periodic boundary conditions in the stream wise direction.  To do this I THINK? I must proscribe a pressure drop to drive the flow.  To do this I THINK? I must edit the user subroutine ustsns.f90 to change the source term in the momentum equation.  I have never used python before, but it seems pretty straight forward to read and edit the user routine file.  Do you think I am headed in the right direction hear or do you know of a better way to proceed or am I totally wrong.
 
Issue 3)
 
Calculation of the Mean Velocity.  To get this from Code Saturne I will have to edit the user subroutine usproj.f90. which is user defined output subroutine.  Am I in the right track ?
 
I have attached some files as zipped that I thought might help you understanding my problem.
Thanks and Regards,
Debashis
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James McNaughton

Re: Problem in simulations

Post by James McNaughton »

This may be of interest to you especially regarding the periodicity and pressure drop -
http://cfd.mace.manchester.ac.uk/twiki/ ... leTutorial
 
James
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