DNS OF TURBULENT JETS ISSUING FROM ACOUSTICALLY LINED PIPES AT DIFFERENT MACH NUMBERS

Abstract

A series of Direct Numerical Simulations (DNS) was performed of fully turbulent jets with a target Reynolds number, based on nozzle diameter, of Re jet = 8,000. The simulations included a long pipe in order to let the flow develop to a fully turbulent state before exiting into a laminar co-flow, and in order to ensure that all possible noise generation mechanisms are represented. Particular attention was paid to minimizing internal noise in the pipe as it was shown in previous studies to contaminate the overall far field noise and make the study of jet-mixing noise difficult. This was achieved by including liner boundary conditions inside the pipe and by modifying the turbulent inflow boundary condition of the pipe. The sound radiation from the pipe/jet configuration was decomposed into its azimuthal Fourier modes and analyzed using a phased array source breakdown technique in order to separate sources associated with jet noise mechanisms from additional noise sources that can be attributed to internal noise or unsteady flow past the nozzle lip. The behaviour of the jet noise source was then studied as a function of jet exit Mach number. Using this approach, we were able to establish the Mach number scaling of the individual azimuthal Fourier modes of far field pressure for the jet mixing noise component.