Computation of Shock Cell Structure of Dual Stream Jets for Noise Prediction

Abstract

Broadband shock cell noise is an important component of aircraft interior noise during cruise. At cruise, the secondary jet of most modern day jet engines is supersonic. As a result, a shock cell structure develops in the jet plume. The interaction of large turbulence structures of the jet flow and the periodic components of the shock cells results in the emission of highly directional broadband shock cell noise. The primary objective of this investigation is to develop a computational method to calculate the shock cell structures ofdual-stream jets issued from separate flow nozzles. Computation of the Fourier modes of such shock cell structures is also considered. Based on the dominant wave numbers computed by the method developed, the frequencies at the peaks of broadband shock cell noise spectra at various radiation directions are calculated. Good agreements are found with experimental measurements over a wide range of primary and secondary jet Mach numbers. The good agreements provide a validation of the accuracy of the computation method.