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-   -   Airfoil Mesh for DES Analysis - y+ Value (http://www.cfd-online.com/Forums/main/13396-airfoil-mesh-des-analysis-y-value.html)

asd April 30, 2007 04:59

Airfoil Mesh for DES Analysis - y+ Value
 
Hi, I have tried to achieve a mesh where y+ is < 1 for airfoil analysis, although found that an excessive number of nodes are required. This is based on the requirement that the aspect ratio of cells within the BL cannot exceed 10. As a result i have specified a constant interval size on the surface such that the normal wall distance is within an allowable limit based on the required y+ value and that the width of the node points on the surface give an AR of 10 (which i was told is the maximum allowable limit for DES analysis). I have found, although possible, the total number of nodes required on the airfoil alone are in excess of 4000-5000 is some cases!!! I am not sure if i am adopting a correct method in the way i mesh my airfoil, so would be interested to know how people have gone about this problem. is there an alternate method which can improve this?

tom May 3, 2007 10:13

Re: Airfoil Mesh for DES Analysis - y+ Value
 
theoritically DES is made to remove this kind of limitation. In LES you must ensure that the AR is limited to capture all the turbulent eddies, but since, in DES, your boundary layer zone is resolved using the RANS equations (Spalart-allmaras) there is no limitation on the AR. Nevertheless try to use values smaller than 1000, and refine your mesh at the leading and trailing edges. Moreover, you should use a progression ratio (ratio between h1 and h0, hn and h(n-1)) no larger than 1.25.


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