Numerical Simulation of the Downstream Fan Noise and Jet Noise of a Coaxial Jet with a Shielding Surface

Abstract

This paper presents an application of a Computational AeroAcoustics (CAA) hybrid process to the two-dimensional numerical prediction of the downstream fan noise and the (subsonic hot) jet noise of a coaxial engine, including (i) the acoustic refraction effect resulting from the propagation through the highly sheared jet mean flow and (ii) the potential acoustic shielding effect of a solid extension of the lower part of the nozzle secondary exhaust. The CAA hybrid methodology associates two different acoustic methods. Firstly the near and mid field propagation through the non-uniform mean flow is computed with an Euler, high order, finite differences solver. Then the far field noise is computed by use of a classical Kirchhoff integration. First computations in a fluid at rest are validated against BEM simulations. Then the simulations are performed including the jet viscous mean flow previously computed with a RANS solver. These computations show that the acoustic shielding of fan noise by the after-body surface is strongly modified when the jet mean flow is included in the simulation. For the jet noise simulation, an equivalent source term is derived from the RANS k-H flow-field, based on a quadrupole distribution. A comparative study shows that the potential acoustic shielding effect is less favourable to the jet noise than to the downstream fan noise.