[S.J.Daniels]

Hi everyone,

Can someone please send me the matlab code as well? - sjd1e11@soton.ac.uk.

Many Thanks,

Steven

[Soder]

Hi,
I would also be interested in the code, and would be very thankful if I could get it
martins@mech.kth.se

/Martin

[nikizat]

hi,

i'm doing my undergrad final year prjct on simulation of atmospheric boundary layer in wind tunnel.....have to measure wind profile, turbulence intensities and turbulence spectrum....

can anybody help with the turbulence spectrum....what i need to measure...how to get the plot?

thank you in advance

[KidMoD]

wow aye
doing spectum always does my head in everytime :\
i suck at this T__T

[kgoodwin]

I am also trying to compute the turbulence energy spectrum for some velocity data I have.

My data are taken with a profiling ADV so I have u, v, w velocities for 12 points along a depth profile. These data are collected over time, which is used for a x-space proxy.

In short, I have u, v, w velocity data spatially distributed across x and z dimensions (only one point in y-direction). So, 3 matrices that are 1501 (x) by 12 (z), one each for u, v, w.

I understand all the steps of calculating the energy spectrum. My only problem is that I'm not sure I completely understand the autocorrelation step in Pope, especially with respect to my data.

R_ij(r, x) = <u_i(x) u_j(x+r)>
The <> notation is an average, correct? What does this mean for a scalar? Or is this the dot product notation? Again what does this mean for a scalar?

If anyone has any matlab code for this portion that they are willing to share, it would be helpful.

Thanks!

[FMDenaro]

just consider a 3d Cartesian mesh and (j,k) some fixed positions. This is some lines of my Matlab code for the energy spectrum

% ____________ E_uu (stream-wise)______________
% ff is a dump array for using the FFT of the field u(i,j,k)
for i = 1:np+1, ff(i) = u(i,j,k); end
% Discrete transform: computation of the Fourier coefficient
c=fft(ff,np); for q = 1:np, c(q)=c(q)/np; end
% Computation of the modulus squared. Cycle for all the wavenumbers
for q=1:np, cu(q,k)=c(q)*conj(c(q)); end

Then, you must simply plot your power spectrum.
Generally, the computed spectrum are also computed along the whole homogeneous directions (e.g. for all the k) and then averaged to have a statistically meaning.

[kgoodwin]

Thank you for your code, FMDenaro. However, it's difficult for me to understand your process without your data. Does anyone have the math formulas they used for the autocorrelation? Again, the steps I'm using are:
1. Calculate autocorrelation to get signal into wave number space
2. Take fft
3. Calculate energy
E(k) = E(k) + abs(V(i,j,m))^2 + abs(U(i,j,m))^2 + abs(W(i,j,m))^2;
4. plot energy vs wave number

[ehsankf]

modes should change from -N/2:N/2.

[babakflame]

Dear FMDenaro

Thanks for sharing ur code.