Q) What size mesh should we use for LES and DES calculations?
A) In general with LES you want to put the cut off point (i.e. cell size) of the small eddies to be in the inertial sub-region.
This is the linear region (with a slope of -5/3) of the plot of logE v frequency.
For DES, for the LES regions you should apply the above advice.
Regarding aspect ratios. f you have large aspects rations you are introducing anisotropy into the turbulent so effectively you might be only getting the benefit of the largest of the cell edges. Also, you can get into stability issues when you have too large (> 5 or 10) aspect ratios.
With respect to cell size expansion you will start getting into trouble if this is larger than 1.2. It can be better for expansion to use a tet grid in terms of stability, but there be issues of diffusion (which will aid stability!).
For more information I would have a look at some of the literature, for example Piamelli.
There are also some paper we have on SAS modelling which looks at some of these issues. Please contact the Helpdesk at ANSYS Europe Ltd.
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Q) What size mesh should we use for LES and DES calculations? A) In general with LES you want to put the cut off point (i.e. cell size) of the small eddies to be in the inertial sub-region. This is the linear region (with a slope of -5/3) of the plot of logE v frequency. For DES, for the LES regions you should apply the above advice. Regarding aspect ratios. f you have large aspects rations you are introducing anisotropy into the turbulent so effectively you might be only getting the benefit of the largest of the cell edges. Also, you can get into stability issues when you have too large (> 5 or 10) aspect ratios. With respect to cell size expansion you will start getting into trouble if this is larger than 1.2. It can be better for expansion to use a tet grid in terms of stability, but there be issues of diffusion (which will aid stability!). For more information I would have a look at some of the literature, for example Piamelli. There are also some paper we have on SAS modelling which looks at some of these issues. Please contact the Helpdesk at ANSYS Europe Ltd. |
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