Exhaust mixing noise computed from time-accurate simulation of compressible free jet turbulence

A computational fluid dynamics model for free, heated jet flow and resultant far-field sound has been developed which uses large-eddy simulation (LES) and Lighthill’s acoustic analogy. A subgrid scale model for small-scale compressible turbulence is employed incorporating a combination of the popular Smagorinsky model and a deductive model. The model has been tested using published experimental mean flow field and rms fluctuation data [W. R. Quinn and J. Militzer, Phys. Fluids 31(5) (1988)] for a turbulent free square jet. The ultimate objective is to address large Reynolds number, high subsonic (compressible) flow with realistic geometries more representative of aircraft engine exhausts than typically considered using direct numerical simulation (DNS). The far-field sound and directivity is computed using the time-derivative form of Lighthill’s source-integral result formulated in terms of quadrupole sources from the simulated flow field, which is integrated in time and contains the fluctuations set up by the time-varying stress tensor. Simulation for a WR 19-4 turbofan engine exhaust (Re≊2×106 based on exit velocity and diameter) was performed, and propagated jet noise results compared with experimental acoustics data.