Turbulent boundary layer resolution

deji · June 15, 2011, 08:31

Hey there Foamers. I am doing Large Eddy Simulation of turbulent natural convection boundary layers, and would like to ask if any of you experts can tell me the "conventional" methodology as to how many grid cells are required to resolve the boundary layer. Someone told me 35, and I just think that is too low. I currently have roughly 60 grid cells within the boundary layer.

So can anyone advice and possibly refer me to some references that discuss this particular issue.

Best regards,
Deji

nsf · June 15, 2011, 13:03

Hi Deji,

I'm no expert but my advice would be not to focus on the number of cells but rather their size and distribution.

First cell should have a $y^+ \approx 1$ . Then use a geometric series with a factor of no more than 1.1.

I.e the cell height of the second cell should be at most 1.1 times the first cell. Third cell height should be less than 1.1 times the second cell height and so on...

Perhaps even a factor no greater than 1.05 should be chosen.

You should also have a look at the spanwise

and streamwise

values.

Best Regards

Nicolas

deji · June 15, 2011, 13:57

Hey there Nicolas. Thank you so much for the feedback.

Deji

June 15, 2011, 08:31	Turbulent boundary layer resolution	#1
deji Senior Member n/a Join Date: Sep 2009 Posts: 199 Rep Power: 16	Hey there Foamers. I am doing Large Eddy Simulation of turbulent natural convection boundary layers, and would like to ask if any of you experts can tell me the "conventional" methodology as to how many grid cells are required to resolve the boundary layer. Someone told me 35, and I just think that is too low. I currently have roughly 60 grid cells within the boundary layer. So can anyone advice and possibly refer me to some references that discuss this particular issue. Best regards, Deji

June 15, 2011, 13:57		#3
deji Senior Member n/a Join Date: Sep 2009 Posts: 199 Rep Power: 16	Hey there Nicolas. Thank you so much for the feedback. Deji nsf and atg like this.

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June 15, 2011, 13:03		#2
nsf Senior Member Nicolas Edh Join Date: Mar 2010 Location: Uppsala, Sweden Posts: 123 Rep Power: 18	Hi Deji, I'm no expert but my advice would be not to focus on the number of cells but rather their size and distribution. First cell should have a $y^+ \approx 1$ . Then use a geometric series with a factor of no more than 1.1. I.e the cell height of the second cell should be at most 1.1 times the first cell. Third cell height should be less than 1.1 times the second cell height and so on... Perhaps even a factor no greater than 1.05 should be chosen. You should also have a look at the spanwise and streamwise values. Best Regards Nicolas