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Offset when calculating TKE using autocorrelation

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Old   February 22, 2021, 07:32
Default Offset when calculating TKE using autocorrelation
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Fab
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Hey CFD Community,

I simulated a free jet stream in Ansys CFX and want to plot the Turbulence Kinetic Energy of my Simulation. In my Simulation I computed a variable which tracks the unresolved Turbulent Kinetic Energy. Now Im using Matlab to calculate the TKE with the components of the velocity vector. The two graphs have a similar trend, but you can see an offset in the y-values. I attached the two graphs below.

I guess there is something wrong with my calculation, am I missing something? The relevant part is the following:

for Wort=1:words
Bereich=Liste(Wort);
for d=1:1:datapoints
spalte=d+(Wort-1)*datapoints;
dstring=int2str(d);

energy_vel(:,spalte)=(P2Y_fluc_win_han(:,spalte).* conj(P2Y_fluc_win_han(:,spalte)))/(N^2);

end
end

for d=1:1:datapoints
energy_tot(:,d)=energy_vel(:,d)+energy_vel(:,d+dat apoints)+energy_vel(:,d+datapoints*2);
end
Attached Images
File Type: png Total_EnergySpectrum_Frequency10.png (60.2 KB, 8 views)
File Type: png resTKEmon_10.png (59.1 KB, 4 views)
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