Fourier Transform of experimental Data

Question

I've tried to do a fast fourier transform in Matlab of some data taken from an experiment in the windtunnel trying to show the frequency of the velocity variation in a flow, but somehow I keep on getting 0Hz as the main frequency. Anyone has encountered this problem before and knows how to solve it or can explain me a bit better how to do the frequency transform.

Ps: It seems to be doing the fast fourier transform alright, the problem might be when converting the data from imaginary to real values

Help me please!

Thank you!

Answer 1

This is a pretty normal thing to encounter. The 0 Hz component (often referred to as the DC component in analogy to the electrical equivalent) is the constant, non-time-varying component of the data -- it's equivalent to the mean of the data. If you have data that does not have a mean of zero, this is a very normal thing to see.

If you want to, you can calculate the mean and then subtract it from your data series, but this is not really necessary, since it will only change that DC component of the FFT. If you're not interested in the DC component for your purposes, you can simply ignore it.