Fast Fourier Transform

Lourival

Hi everyone, I would like to analyse the turbulent spectrum of the flow over a bluff body. As I'm simulating using FLUENT all the data is on the Spatial space and I need to use FFT to transform the data to the Fourier space.

In order to compare my simulation with other results I got the velocity (U, V, W) on the same point that the paper presented. Also I have the code to compute the FFT. So my question is about how to do it.

To obtain the spectrum, should I use the FFT of the V velocity and from the results get the square ? For example:

FFT(V) = R+iIm

The one dimensional streamwise velocity spectrum is R^2+Im^2 plotted in a log graph? What about the frequency on the X axis? How do I calculate? Does any one know about it?

Thanks

Lourival