I'm simulating fully developed turbulent pipe flow.

I need to calculate the energy spectrum.

I used MATLAB with its FFT function (fast fourier transform) to compute the energy spectrum.

The trend of the energy spectrum is good but it is in an oscillating form.

Does any body have an idea to compute the energy spectrum ?

Thank you

Hi,

Perhaps you can try to divide the wave number range into small intervals.Then integrate the energy of all energy components with a wave number in a certain interval and scale it with the size of the bin. This will give you a kind of average and will smooth out the oscilations. Don't take the bins too large because then you smooth out the complete spectrum.

Tom

I did not understand what you exactly mean.

Would you please explain in detail ?

Thank you

the spectrum is a kind of averaging. If it is oscillation, enlarge the range of averaging. In spectral space, it means enlarge the interval between modes. For example if the interval is -0.1 < k < 0.1 before, now you use -0.5 < k < 0.5. ( it is just an example, don't use it directly)