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 (Tam, C. K. W., and Auriault, L., "Jet Mixing Noise from Fine Scale Turbulence," AMA Journal, Vol. 37, No. 2, 1999, pp. 145 153), 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 kappa Epsilon turbulence model is provided. It is shown that the computed mean flow profiles are in good agreement with experiment. Extensive comparisons between computed noise spectra and measurements are reported. They include dual stream jets from separate flow nozzles with and without an external plug. Jets operating at different combinations of primary and secondary jet Mach number and temperature ratio are considered. The bypass ratios range from 1.5 to 8.0. Effects of forward flight are also included in the comparisons. Good agreements are found not only in spectral levels but also in spectrum shapes and directivities over many sets of data.[PUBLICATION ABSTRACT]