comparison with DNS

hars88 · May 17, 2012, 20:18

I have been trying to perform CFD analysis of isotropic turbulence using LES like scheme. In order to compare my results with DNS,should I be finding the parameters like intergral length scale(to find turn over time) from my scheme or take the DNS value. Thanks a lot......

FMDenaro · May 18, 2012, 05:17

Quote:

Originally Posted by hars88

I have been trying to perform CFD analysis of isotropic turbulence using LES like scheme. In order to compare my results with DNS,should I be finding the parameters like intergral length scale(to find turn over time) from my scheme or take the DNS value. Thanks a lot......

compare the statistics (RMS, energy spectra), also total energy decaying (if your case is not forced) in time

hars88 · May 18, 2012, 18:44

Hi, thanks a lot for the reply.... when i want to plot the total energy for example, the time axis is generally non-dimensionalized which involves a length scale(integral length scale). should i obtain this value from a DNS or calculate from my code?... thnx a lot

FMDenaro · May 19, 2012, 05:16

in homogeneous isotropic flows the characteristic lenght scale is generally the Taylor micro-scale lambda, on whcih the Reynolds number of the computation is based too. Use information from DNS as in LES you have a cut-off of the smallest scales (only scales in the inertial range are computed) and you cannot compute the Taylor length.

hars88 · May 21, 2012, 19:37

thanks a lot for clarifying......

May 17, 2012, 20:18	comparison with DNS	#1
hars88 New Member hars Join Date: May 2012 Posts: 4 Rep Power: 14	I have been trying to perform CFD analysis of isotropic turbulence using LES like scheme. In order to compare my results with DNS,should I be finding the parameters like intergral length scale(to find turn over time) from my scheme or take the DNS value. Thanks a lot......

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May 18, 2012, 18:44		#3
hars88 New Member hars Join Date: May 2012 Posts: 4 Rep Power: 14	Hi, thanks a lot for the reply.... when i want to plot the total energy for example, the time axis is generally non-dimensionalized which involves a length scale(integral length scale). should i obtain this value from a DNS or calculate from my code?... thnx a lot

May 19, 2012, 05:16		#4
FMDenaro Senior Member Filippo Maria Denaro Join Date: Jul 2010 Posts: 6,865 Rep Power: 73	in homogeneous isotropic flows the characteristic lenght scale is generally the Taylor micro-scale lambda, on whcih the Reynolds number of the computation is based too. Use information from DNS as in LES you have a cut-off of the smallest scales (only scales in the inertial range are computed) and you cannot compute the Taylor length.

May 21, 2012, 19:37		#5
hars88 New Member hars Join Date: May 2012 Posts: 4 Rep Power: 14	thanks a lot for clarifying......