Dear,

you can just compute the pressure field, then take FFT. Do you mean the FFT algorithm ? code ? 

The easiest way for you, I think, is use MATLAB, there is a function "fft"  and inverse FFT "ifft". It's very easy to use. See the following link:

http://www.mathworks.com/help/matlab/ref/fft.html

Best,

http://www.mathworks.com/help/matlab/ref/fft.html

I don't know what a URANS simulation is, but an FFT is an efficient implementation of a DFT. A DFT fits complex sinusoids  to temporal/spatial data. Just a warning - if your data does not contain extended periodic fluctuations then Fourier analysis is pretty much meaningless. Why do you need to apply an FFT?   

Thanks for the response. Yes I'm looking an efficient algorithm code. Because I saw some on internet but very complicated to read through. Some a for 2D some multi-dimensional and I getting confuse by that. 

To compute acoustic sound a point for example do to turbulence field, one compute the CFD (RANS turbulence model) to get the velocity field and from that convert it to fft data for computing the acoustic sound propagation using Lighthill acoustic analogy for example.

Hi Hugh !

Please what do mean by "extended periodic fluctuations" ?

Dear Gokpi:

I am not clear on the final objective of your work. If you are searching for some frequencies you use FFT. It is very easy with MATLAB, ORIGIN or STATISTICA for example.

Cheers Humberto

What about run yor CFD model in OpenFOAM and postprocess the data with its noise utility, it manage the data and the outputs are files to plot:

- FFT of the pressure data

- narrow-band PFL (pressure-fluctuation level) spectrum

- one-third-octave-band PFL spectrum

- one-third-octave-band pressure spectrum

Regards.