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mesh guidelines for reattachment

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Old   July 19, 2006, 09:54
Default mesh guidelines for reattachment
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Ralf Schmidt
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Hi!

what are the guidelines, meshing the zone at the wall, where e.g. reattachment takes place?? I am using k-e and k-w turb. modells with different wall functions. Results are ok, except close to the reattachment point (cylindrer in axial flow).

Is ther a y+ value, that has to be considered?? y+ values for the wall are well known... but they are valid only for equilibrium BL. Also, y+ is allways zero at the reattachment point!

Any suggestions??

Ralf
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Old   July 20, 2006, 06:48
Default Re: mesh guidelines for reattachment
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Salvatore
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Hi Ralf, I analysed the same problem. In the reattachment point, it's difficult to achieve solutions similar to sperimental measures, also if you refine the mesh a lot. I suggest you to begin from a coarse mesh with a few points and gradually refine it until you achieve a small numerical difference between the fine mesh and its previous.

Since the problem in reattachment point is not mesh dependent, to study turbulente flow and its laminar sublayer, the y+ should be on the order of unity (y+<5).

y+ dependes on the wall friction stress. The wall friction coefficient is always zero at separation and reattachment point, then y+ must be zero in the same points.
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