An approximation method to identify the near-field sound patterns in aerodynamic flows

This work presents an approximate method to identify the propagating sound patterns in evolving aerodynamic flows based on an indirect acoustic variable approach. The key measure is to filter out the non-acoustic hydrodynamic components by applying a differential operator on the flow fluctuation variables, leading to an indirect acoustic variable. The differential operator was based on the fact that the convection motion dominates the motion of the non-acoustic hydrodynamic fluctuations, so Taylor’s hypothesis can be employed. Once the indirect acoustic variables are obtained, the pressure fluctuation relating to the acoustic waves can be reconstructed by solving an alternative differential equation that governs the sound propagation. In this work, we apply the method for the problem of noise generation from a mixing layer. Comparisons of the reconstructed sound pressure distribution with the direct numerical simulation data are made, showing that the proposed method can capture the radiating sound pressure well whilst the convecting non-acoustic components are well filtered out.