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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.

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A hybrid method of aeroacoustic noise computation based on Lighthill's Acoustic Analogy is applied to investigate the noise radiated by a low Mach number flow through a ducted diaphragm. The simulation method is a two-step hybrid 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 aerodynamic quantities are recorded. In the second step, a variational formulation of Lighthill's Acoustic Analogy using a finite element discretization is solved in the Fourier space. The sensitive steps consisting in computing and transferring source term data from the fluid mesh to the acoustic mesh are reviewed. Indeed, as fluid and acoustic meshes have different constraints due to the different wavelengths to be resolved, interpolation is required. The method is applied to a three-dimensional ducted diaphragm with low Mach number flow. Although the configuration is symmetric, this study exhibits a very complex three-dimensional flow behavior. Four different aerodynamic solutions are compared with the Direct Noise Computation performed by Gloerfelt & Lafon. Good agreement is found in terms of mean flow as well as on instantaneous behavior and turbulent intensities. Acoustic computations are performed with different mesh refinement and interpolation methods. Comparison with literature data on similar cases shows the method relevancy.