# LES correlation and turbulent energy spectrum

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 October 13, 2005, 14:21 LES correlation and turbulent energy spectrum #1 Fabian Guest   Posts: n/a Hi, I want to calculate the turbulent kinetic energy spectrum from my LES data to do one step in the validation process, but I am little bit confused about it. There are two choices, one is to create a energy spectrum in space, where I have to find a homogenous direction, and the other to create a spectrum in time, where I have to choose a certain point in domain. The problem is, which variant should I use and esp. which plane for the spectrum in space and which point in a surface-mounted cube simulation? To calculate the spectrum I have to caculate the autocorrelation or cross-correlation, depending on the choice space/time. There exist an octave/matlab function 'xcorr' which can do that, but I would like to do that without using that function and without the use of FFT. Would be nice if anybody has an idea! Fabian

 October 13, 2005, 18:07 Re: LES correlation and turbulent energy spectrum #2 sss Guest   Posts: n/a For space: invoke Taylor's frozen field hypothesis, For time: simply take FFT of the velocity signal

 October 17, 2005, 01:32 Re: LES correlation and turbulent energy spectrum #3 Fabian Guest   Posts: n/a Hi, thanks, do you have an idea which point (time) or plane (space) I should choose for a surface mounted cube calculation. I mean, I could try to find the best point which gives me Kolmogorovs -5/3 slope... Fabian

 October 17, 2005, 05:13 Re: LES correlation and turbulent energy spectrum #4 Lionel Larchevêque Guest   Posts: n/a In order to have a chance to find a -5/3 slope generally related to a wall-free turbulence at equilibrium, I suppose that the measurement point should be located in the wake and a few cube length away from the aft wall.

 October 18, 2005, 02:04 Re: LES correlation and turbulent energy spectrum #5 Fabian Guest   Posts: n/a Hi Lionel, thanks for the information. I see how this works. Greetings! Fabian