Improved Method for Prediction of Noise from Single Jets

Abstract

The prediction of jet noise from first principles has proved to be elusive. Practical methods rely on empirical correlations of experimental measurements, supplemented by some theoretical considerations and ad hoc functions. Clearly, these empirical methods are only as good as the databases on which they are based. An experimental aeroacoustic database of high quality created by the author and subsequent scaling laws derived using the database have facilitated the development of an accurate prediction method. The scaling laws, wherein the spectral shape at any radiation angle is expressed as a function of the jet velocity ratio and the jet stagnation temperature ratio, allow the spectra at different jet velocities but at a fixed jet stagnation temperature to be collapsed to a single curve at each radiation angle. Thus, master spectra as a function of the Strouhal number are developed. No additional empiricism or other factors are needed. The range of the Strouhal number has been extended considerably through the use of nozzles of different diameters and the acquisition of accurate data up to a one-third octave center band frequency of 80 KHz. The master spectra developed here can be used to predict the turbulent mixing noise as well as check the quality of the data.