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#1 |
New Member
Matej Andrejasic
Join Date: Sep 2010
Posts: 2
Rep Power: 0 ![]() |
Dear All,
I'm simulating airflow passing a propeller using MRF. I'm using incompressible solver simpleFoam and kOmegaSST turbulence model with nutkWallFunction as a wall function at nut. I don't have problems with simulations, it converges beautifully to nice results, but I would like to ask how do I calculate yPlus in my situation? Since it is High-Re type of simulation I ran yPlusRAS utility, but resulting yPlus is not ok even though I recalculated U by adding \omega x R (rotating term). After a little bit of research in doxygen I found that since I'm using nutkWallFunction the utility yPlusRAS consequently uses equations: u_{\tau}=C_{\mu}^{1/4}\sqrt{k} together with y+ definition y+=y u_{tau}/\nu. Since turbulent kinetic energy k is being calculated in rotating frame of reference it apparently doesn't result in correct y+ calculation?!? Then I changed kOmegaSST in constant/RASProperties to SpalartAllmaras and I changed all nutkWallFunction in nut file to nutUWallFunction in the last simulation time folder. Then I ran yPlusRAS again and this time it calculated "logical" y+ distribution. nutUWallFunction uses an iterative calculation in order to calculate y+ described in: http://www.cfd-online.com/Wiki/Two_equation_models (standard wall function). Since I ran simulation with nutkWallFunction and calculated yPlus with nutUWallFunction I don't know what to think about these results?!? How do you calculate yPlus in MRF? Thank you very much for your help. Best Matej |
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#2 |
Senior Member
M. Montero
Join Date: Mar 2009
Location: Madrid
Posts: 153
Rep Power: 17 ![]() |
Dear MatejAndrej,
Excuse for using this same topic but I think you can help me the little I need. I am trying to use the same approach that yours to simulate a wind turbine using MRF approach. All goes ok until I activate turbulence ( I am trying to detect where the problem is). For the walls inside the rotating region I have put nutkWallFunction, KqRWallFunction and epsilonWallFunction. I have also tried nutUSpaldingWallFunction with no luck Is it needed to change in some way the wall function for MRF? The k and epsilon values at wall increase a lot and then the simulation crash. I am using OF2.3.x and kEpsilon model ( the mesh is ready for y+ around 100) |
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Tags |
mrf, nutkwallfunction, nutuwallfunction, yplus |
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