Tonal noise prediction of propellers in ambient flow using steady-state CFD and Ffowcs Williams-Hawkings formulations

As electric vertical take-off and landing (eVTOL) concepts and urban air mobility gain prominence, the mitigation of propeller noise has become essential. This study presents a comprehensive assessment of acoustic prediction methodologies, focusing on the application of both Formulation-1A and the more recent Formulation-1C of the Ffowcs Williams-Hawkings (FWH) equation. The work demonstrates the use of steady-state Reynolds-averaged Navier-Stokes (RANS) simulations with a single rotating frame (SRF) approach for efficient acoustic analysis, enabling the transformation of steady flow solutions into time-varying acoustic surface data. The methodology is implemented as a new class within the open-source libAcoustics library for OpenFOAM, leveraging its parallelization capabilities. Validation with experimental data and comparison against numerical results were performed for a range of propeller configurations. Comparative analysis with direct noise computation (DNC) highlights the improved accuracy of Formulation-1C, especially in scenarios with ambient flow, and demonstrates the limitations of Formulation-1A in such conditions. The results confirm the robustness of the proposed framework for propeller noise prediction across a range of operating regimes.