[VictorCunha]

Hi,

That`s the first time I'm calculating energy spectrum and I have seen many examples of calculating the spectrum by using the FFT of the velocity components and then scaling it accordingly. However, I am trying to plot the spectrum using the spatial correlation function and FFT of that. I am not sure about scaling in the frequency. My plot does not show the decaying region.

I am using E11(k) = FFT(R11(x)/2) relation.

Lz=16;%length in the x direction
R11 = autocorr(u_prime, length(u_prime)-1);
NFFT = 2^nextpow2(length(R11)); % Next power of 2 from length of L
Y = fft(R11/2,NFFT);
E = Y.*conj(Y);

f = 2*pi*[0:1:NFFT/2]/Lz;
loglog(f,E),':bs', 'MarkerSize',2);
hold on
loglog(f,10*f.^(-5/3),'r');
hold off

If someone could try this code in a known data set or if there are some huge mistakes, please let me know.