Prediction of flyover jet noise spectra from static tests

A scaling law for predicting the overall flyover noise of a single stream circular jet from static experiments [A. Michalke and U. Michel, J. Sound Vibration 67, 341–367 (1979)] is extended to the prediction of spectra. The theory is based on the Lighthill approach to jet noise. The density terms are retained to include the effects of jet heating. The turbulent flow quantities are assumed to scale with relative velocity. nozzle diameter, and jet density. The jet flow field is assumed to be linearily stretched in flight leading to an increase of both the axial source and coherence length scales in flight. The four cases regarding the flyover or wind tunnel measurement of narrow band or third octave spectra are treated separately. The resulting equations are derived for low flight Mach numbers and for emission angles not too close to the jet axis. The scaling law shows a good agreement with experimental results obtained with the J85 jet engine mounted on the Aérotrain. [Work was completed while the first author held an NRC Senior Research Associateship.]