integral length scale and cross-correlation (with openfoam data, LES pipe flow)

jet · June 4, 2010, 09:07

Hi,
i want to calculate the integral length scale of a pipe flow in matlab.
the pipe flow (LES) is calculated with openfoam-1.6 .
I have read out the velocity components (cell center) of 1000 cells in a preview-folder at a one definite time-step.
Now I have to calculate the cross-correlation function (in x-direction):
1. step: i subtract the mean velocity from the axial-velocity-component in order
to obtain the fluctuating velocity u'

2. step: i calculate the cross-correlation as:

for i=1:1:1000;
ufluct(i)=uflukt(1)*uflukt(i)
end
ucross=ufluct./ufluct(1);
ufluct is the same as u' and ucross should be my cross-correlation coefficient?!
but my problem is, my code does not calculate the time-averaged cross-correlation-coefficient because i don't know wich kind of data i have to time-averaged.

i have read some books about it (Pope, Wilcox, Hinze and Lumley ...) but i can't implement their ideas in matlab.

it would be great if somebody has an idea or could explain me how to calculate the integral length scale correctly!
best regards,

jet

lx882211 · November 7, 2016, 05:23

Hi, can you tell me how to calculate intergral scale, based on Openfoam data? Thank you very much.

June 4, 2010, 09:07	integral length scale and cross-correlation (with openfoam data, LES pipe flow)	#1
jet New Member Join Date: Nov 2009 Posts: 12 Rep Power: 17	Hi, i want to calculate the integral length scale of a pipe flow in matlab. the pipe flow (LES) is calculated with openfoam-1.6 . I have read out the velocity components (cell center) of 1000 cells in a preview-folder at a one definite time-step. Now I have to calculate the cross-correlation function (in x-direction): 1. step: i subtract the mean velocity from the axial-velocity-component in order to obtain the fluctuating velocity u' 2. step: i calculate the cross-correlation as: for i=1:1:1000; ufluct(i)=uflukt(1)*uflukt(i) end ucross=ufluct./ufluct(1); ufluct is the same as u' and ucross should be my cross-correlation coefficient?! but my problem is, my code does not calculate the time-averaged cross-correlation-coefficient because i don't know wich kind of data i have to time-averaged. i have read some books about it (Pope, Wilcox, Hinze and Lumley ...) but i can't implement their ideas in matlab. it would be great if somebody has an idea or could explain me how to calculate the integral length scale correctly! best regards, jet

November 7, 2016, 05:23		#2
lx882211 New Member Mr.liu Join Date: Sep 2012 Posts: 27 Rep Power: 14	Hi, can you tell me how to calculate intergral scale, based on Openfoam data? Thank you very much.