Fourier Transform (Spectral analysis)

tayfun

Hello to all!

A short summary of my task: I am simulating a supersonic flow (M=1.5) through a rectangular channel over a cavity on the bottom of the channel with Fluent 6.1. The calculations are unsteady (time step 1x10e-6). In order to investigate the pressure oscillations on the top wall of the channel (opposite of the cavity) I define points at the top wall and write the pressures over time in a .OUT file.

Problem:

If I want to do a FFT analysis to plot the Pressure over the frequency I obtain untrue results. Is there a other way in fluent to present the pressure oscillations?

Thank you, for any response!