Separate Flow Nozzles Research Articles

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

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.

Fine-Scale Turbulence Noise from Dual-Stream Jets

Nowadays, commercial aircrafts, invariably, use high-bypass-ratio dual-stream jets for propulsion. As yet, there is still an urgent need for an accurate physics-based noise prediction theory for jets of this configuration. Thus, an investigation is made to determine whether the Tam and Auriault theory, originally developed for predicting the fine-scale turbulence noise of single-stream jets, is capable of predicting accurately the fine-scale turbulence noise of dual-stream jets from separate flow nozzles operating at various bypass ratios. The configuration of a separate flow nozzle is fairly complex. Hence, the jet flow and turbulence in the nozzle region and in the region immediately downstream are also fairly complex. However, these are also the most important noise source regions of the jet. To enable an accurate computation of the mean flow and turbulence level in these regions, a computational aeroacoustics marching algorithm for calculating the parabolized Reynolds averaged Navier-Stokes equations supplemented by the k-e turbulence model is provided