Sound amplification at T-junctions with merging mean flow

Abstract

This paper reports a numerical study on the aeroacoustic response of a rectangular T-junction with merging mean flow. The Mach number of the grazing flow in the main duct is fixed at 0.1. The primary motivation of the work is to explain the phenomenon of high level 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-e turbulence model. It is found that the base flow changes significantly with the presence of a small bias flow. Compared to pure grazing flow, a strong shear layer is created in the downstream main duct, starting from the T-junction trailing edge. That is, the main region of vortex-sound interaction is moved away from the junction to a downstream region much larger than the junction width. The flux of fluctuating enthalpy is calculated to estimate the acoustic source power due to the fluid sound interaction.