I do an LES simulation. How do I deduce the turbulent energy spectrum from my simulation. The text books say to use velocity correlations, but I am a beginner and can someone tell me step by step how to find it from my simulation. Thanks. Yui

It depends on what spectrum are you trying to find. What I did was installed pressure probes to acquire pressure signal and take the FFT of this time signal.

I used Matlab, but I am not 100 % sure I did it right: I dont know if such spectrum would follow Kolmogorovs law at all...

Can someone clarify that?

if you want i can send you the piece of Matlab code for that...

i am trying to retreive a -5/3 spectrum. thanks for your answer but i want to know how to get it from a computational simulation not experiement.

When investigating the 5/3rd Kolmogorov's Law, people are usually refering to spatial variation of kinetic energy. Hence, you need a very simple geomtry and you need to determine the kinetic energy associated with scales of different wavelength. The usual plots one sees, are simply plots of the energy versus the wavenumber. The energy spectrum has nothing to do with temporal evolution of these scales -- please correct me if I am wrong.