A Hybrid LES/CAA Method for Aeroacoustic Applications

Abstract

This paper describes a hybrid LES/CAA approach for the numerical prediction of airframe and combustion noise. In the hybrid method first a Large-Eddy Simulation (LES) of the flow field containing the acoustic source region is carried out from which then the acoustic sources are extracted. These are then used in the second computational Aeroacoustics (CAA) step in which the acoustic field is determined by solving linear acoustic perturbation equations. For the application of the CAA method to a unconfined turbulent flame, an extension of the method to reacting flow fields is presented. The LES method is applied to a turbulent flow over an airfoil with a deflected flap at a Reynolds number of Re = 106. The comparison of the numerical results with the experimental data shows a good agreement which shows that the main characteristics of the flow field are well resolved by the LES. However, it is also shown that a zonal LES which concentrates of the trailing edge region on a refined local mesh leads to a further improvement of the accuracy. In the second part of the paper, the CAA method with the extension to reacting flows is explained by an application to a non-premixed turbulent flame. The monopole nature of the combustion noise is clearly verified, which demonstrates the capability of the hybrid LES/CAA method for noise prediction in reacting flows.