Effect of compressibility on flow-induced noise predictions at low Mach numbers

Research on fluid dynamics and flow-induced noise at low Mach numbers (M<0.3) holds significant scientific importance. However, conventional numerical simulations for low Mach number flows often assume incompressible fluids, although the medium is compressible to allow sound wave propagation. In this study, we investigated sound generation from canonical flow configurations at low Mach numbers ranging from 0.05 to 0.30: flow around a cylinder, gust–airfoil interaction, and turbulence–airfoil interaction. Both incompressible and compressible numerical models were employed to assess their performance in predicting fluid dynamics and acoustic fields. Furthermore, the Ffowcs Williams and Hawkings (FW–H) equation is also employed to predict far-field noise radiation, which is further compared to direct numerical simulations. Our findings reveal that the incompressible model is able to predict drag and lift force but fails to capture sound wave propagation. Consequently, near-field sound sources from the incompressible model are unsuitable for the permeable-surface FW–H equation. Although the solid-surface integral form of the FW–H equation provides an effective approach for noise prediction, it exhibits deficiencies in accurately resolving high-frequency (non-compact) acoustic components. In contrast, the compressible model consistently yielded excellent agreement with the reference data across the entire Mach number range, both in direct numerical simulations and FW–H-based acoustic computations.