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appropriate boundary layer properties, k-e turbulence model

Posted Feb 18, 2011, 12:25 p.m. EST Fluid & Heat, Computational Fluid Dynamics (CFD) Version 4.1, Version 4.4 3 Replies

Sylvana Garcia
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Hello,

I have been trying to simulate fluid flow thorugh a certain design, and I'm starting with half a cylinder to which I'll add geometric complexity.

The model does solve. However, the walls don't show velocity zero.

Is this due to the boundary layer properties? the mesh? I don't know where to start. I have tried a few variations on the mesh and boundary layer sizes, but I still have the same result. What are the optimal boundary layer properties for a fluid flow problem?

Thank you,
Sylvana
3 Replies Last Post Feb 22, 2016, 9:37 a.m. EST
Ozgur
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Posted: 1 decade ago Feb 18, 2011, 12:30 p.m. EST
Turbulence models that use wall functions will not show a zero velocity at the boundary because I think what it is plotting "at the boundary" is really not at the boundary but at a certain distance (wall offset, wall liftoff) from the boundary. A good practice is to verify that the use of wall function was justified after solving the model by checking the variable that corresponds to the wall offset (I think in v3.5a it was called dwplus) and make sure that it is within the generally acceptable range of 30-100 or so. Refer to documentation and I am sure you will find more accurate info on this.
Turbulence models that use wall functions will not show a zero velocity at the boundary because I think what it is plotting "at the boundary" is really not at the boundary but at a certain distance (wall offset, wall liftoff) from the boundary. A good practice is to verify that the use of wall function was justified after solving the model by checking the variable that corresponds to the wall offset (I think in v3.5a it was called dwplus) and make sure that it is within the generally acceptable range of 30-100 or so. Refer to documentation and I am sure you will find more accurate info on this.
Sylvana Garcia
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Posted: 1 decade ago Mar 2, 2011, 11:35 a.m. EST
Hello, Ozgur

Thank you very much for your reply. I checked the wall lift-off in viscous units on the surfaces and it does show a value of 11.06, which is OK according to the sample model of the turbulent backstep.

Thanks again,
Sylvana
Hello, Ozgur Thank you very much for your reply. I checked the wall lift-off in viscous units on the surfaces and it does show a value of 11.06, which is OK according to the sample model of the turbulent backstep. Thanks again, Sylvana
Abiodun Jegede
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Posted: 8 years ago Feb 22, 2016, 9:37 a.m. EST
How can I view or calculate y+ value in COMSOL 4.4
How can I view or calculate y+ value in COMSOL 4.4

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