scope:

INTRODUCTION

This Item provides a computerized method for predicting pure jet flyover noise spectra from noise spectra measured from, or predicted for, a stationary jet. The changes in noise levels from static to flight conditions are often referred to as static-to-flight effects. The computational procedure is almost identical to the method described in Derivation 1 and is applicable to single-stream jets with circular nozzles.

There are three basic changes in noise spectra when going from static conditions to flight conditions. The first is the spectral shape change which arises from changes in jet refraction due to flight. The second and third changes are the shifts in amplitude and frequency arising from the effects of motion on the source. The approach used in this Item considers the change in jet refraction by an angle transposition and uses empirical correlations of experimental data to predict amplitude and frequency changes.