[stanking]

I have a question about turbulent energy spectrum !!! Now I have the data of position and velocity at grid.

the data is like this:
X Y Vx Vy

I have already used FFT to transform Vx and Vy to V_kx and V_ky.

Then I calculate the kx = 2*pi*N / L and kx = 2*pi*N / L. (N = 1,2,....)

Here is a question. N is from 0 or from 1???

Now the data is like this:
kx ky V_kx V_ky

How can I calculate the energy spectrum??

1. How can I calculate the k? k = sqrt(kx^2+ky^2), is right?

2. V(k) = sqrt(V_kx^2 + V_ky^2), is right??

3. plot(k,V(K),k^(-5/3))

please tell me the detail of the calculation procedure!!!

thanks!!!