Numerical Applicability of Different Sound Source Formulations to Compute Combustion Noise Using Acoustic Perturbation Equations for Reacting Flows

Combustion noise analyses in a hybrid computational aeroacoustics (CAA) context are presented. Acoustic perturbation equations for reacting flows (APE-RF) describe the wave propagation, while unsteady results from a variable density incompressible reactive large-eddy simulation (LES) are used to evaluate the acoustic source terms. To simulate combustion generated noise via such a hybrid approach, an appropriate source description has to be taken, which preferably matches two requirements, i.e., on the one hand, to efficiently and accurately predict the generated acoustic field, and on the other hand, to easily determine the source term from the LES. In this study, three source formulations for the APE-RF system are examined on two acoustic meshes with different resolutions in the source region to predict the acoustic field of an open turbulent nonpremixed flame. Using the source term, which is expressed via the scaled partial time derivative of the density, the acoustic field can be reproduced best up to a maximum Strouhal number of StD = 2 on the fine mesh. However, for this source formulation spurious noise can be observed depending on the CAA resolution. It will be shown in this study that this observation can be related to the “artificial interpolation induced acceleration” effect. A compromise between efficiency and accuracy represents the source formulation expressed via the scaled material derivative of the density.