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y+ help and suggestions.

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Old   May 2, 2010, 06:39
Default y+ help and suggestions.
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I have a geometry of a car with open wheels and exposed suspension.

I have meshed it using a trimmer mesh with prism layers.

Most of the body is streamlined though the suspension components and wheels are more bluff.

Im not really sure what to do with y+ values, after one 1000 iteration run i have visulised the y+ and it ranges from mostly very small almost zero values to 1025. The high values are seen around the suspension components, and their connections to the main body.

I want to capture the physics of any turbulence created by the model but i also want the detail of the boundary layer as skin friction could be very important. What y+ value range would people recommend, and which physics model is appropriate for the range.

I want to use the spalart allmaras model if possible.
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Old   June 3, 2010, 16:34
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This reply may come in a little bit late, but one thing you may want to make sure is that your highest y+ is in teh order of 100 - 300, so that you capture atleast the log law.

It is very difficult to control the y+ values given the complicated geometries oft encountered in real life. So teh best idea is to look at the 'critical' regions of your analysis and make sure that the y+ values are good.

If you are keen on getting an accurate cf (or h value) it is recommended that you also work with All Y+ Wall treatment that is available in k-e, k-w and SA models in STAR CCM+. This automatically switches between a low Re turbulence model and a high Re model depending on the necessity.
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Old   July 6, 2010, 10:57
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Adjust your prism layer thickness on the boundaries with the high y+ values might help. With 1025 it is completly out of the recommended range, so some of your mesh values are not matching the problem.
The hint of vishyaroon is also very useful.

And I guess, you want to take us for a ride if you want to capture the skin friction on suspension components? Skin friction might be of interrest on the body, but will not be critical on suspension components. In this regions, the most of the drag will be caused by vortices and stuff.

Best regards
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y+ value

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