## Generating Fast Fourier Transforms (FFTs) using ADS-UTIL

### Introduction

ADS-UTIL can be used to generate a Fast Fourier Transform (FFT) for PSUF files generated during an unsteady LEO simulation. This guide shows how to generate the FFT as well as how to plot the power spectrum and to show the Fourier coefficient contours on the aifoil surface.

### ADS-UTIL Output

ADS-UTIL will write out two different files contain information about the FFT:

- A vtk file containing surface contours showing the distribution of fourier coefficients for all harmonics
- The POWER_SPECTRUM.DAT file: Which provides the power spectrum at user specified points on the airfoil

### ADS-UTIL Input

### Plotting Fourier Coefficent Contours

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### Reading and Plotting Power Spectrum Data

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- Harmonic: Indicates the harmonic index of a given row
- Frequency: Indicates the frequency of a given harmonic. If converting an old (Pre-v5.6 LEO) this value may not be computed correctly.
- Amplitude: Indicates the amplitude of the fourier coefficient
- Phase angle: Indicates the phase angle of the given harmonic

A list of harmonics, frequencies, and amplitudes is given for each point location specified in the input files. This data can be easily plotted using any plotting package as shown below.

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**Code**

**Author**

George Fan

**Date Created**

2013-06-23 04:10:42

**Date Updated**

2013-06-23 04:11:56

**Views**

8131