Sound amplification at a rectangular T-junction with merging mean flows

Abstract

This paper reports a numerical study on the aeroacoustic response of a rectangular T-junction with merging mean flows. The primary motivation of the work is to explain the high sound amplification, recently seen experimentally, when introducing a small merging bias flow. The acoustic results are found solving the compressible Linearized Navier–Stokes Equations (LNSEs) in the frequency domain, where the base flow is first obtained using RANS with a k–ε turbulence model. The model predicts the measured scattering data well, including the amplitude and Strouhal number for the peak amplification, if the effect of eddy viscosity damping is included. It is found that the base flow changes significantly with the presence of a small bias flow. Compared to pure grazing flow a strong unstable shear layer is created in the downstream main duct starting from the T-junction trailing edge. This means that the main region of vortex–sound interaction is moved away from the junction to a downstream region much larger than the junction width. To analyze the sound amplification in this region Howe׳s energy corollary and the growth of acoustic density are used.