Numerical investigation of indirect noise generation by accelerated vorticity

Combustion noise of aero engines originates from unsteady combustion processes which in turn lead to vortical and temperature fluctuations. These so-called vorticity and entropy waves are convected from the combustor into the turbine where their acceleration results in an additional sound release, namely the indirect noise. In the present study the noise generation by accelerated vorticity waves is investigated in a convergent-divergent nozzle representing the simplest model of the flow through the turbine. A hybrid CFD/CAA- approach is applied which consists of RANS mean flow simulations followed by frequency domain simulations of linear acoustic and vortical uctuations based on the linearized Navier-Stokes equations (LNSEs). Vorticity waves are excited by a body force term which is deduced from an analytical solution of the linearized vorticity equation. By this means, the indirect noise released by the accelerated vorticity waves is computed and compared with experimental measurements. The numerical simulation captures in general the coupling mechanisms relevant to indirect noise.