Validation of a Hybrid CAA Method. Application to the case of a ducted diaphragm at low Mach number

Abstract

´In this work, a hybrid method of aerodynamic noise computation is first validated, and then applied to investigate the noise radiated by a low Mach number flow through a diaphragm in a duct. The simulation method is based on a two steps approach relying on Lighthill’s acoustic analogy, assuming the decoupling of noise generation and propagation. The first step consists of an incompressible Large Eddy Simulation of the turbulent flow field, during which the Lighthill’s source term is recorded. In the second step, a variational formulation of Lighthill’s Acoustic Analogy using a finite element discretization is solved in the Fourier space. A general validation is performed with the case of two corotating vortices to assess the proper definition of the source term; the exit of turbulent structures from the computational domain is accounted for by a spatial filtering. This method is applied to a realistic three-dimensional diaphragm at low Mach number flow; the aerodynamic flow features are detailed, showing good agreement with both experimental and numerical studies in similar conditions. The acoustic computation is currently in progress.