Investigation of noise prediction for a five-bladed propeller under edgewise flow using permeable Ffowcs Williams and Hawkings surfaces

This study presents a computational investigation of far-field propeller noise under edgewise inflow using Detached Eddy Simulation coupled with the Ffowcs–Williams and Hawkings formulation. The primary contribution lies in evaluating and validating surface size—with and without end cap—and end-cap correction strategies for permeable surfaces, along with a theoretical model for optimal end-cap spacing based on equations from jet-noise theory and Spectral Proper Orthogonal Decomposition. To assess these effects, smaller and larger surfaces with open ends, a single end cap, and two correction approaches—JetEnd and SPODEnd—are tested on a five-bladed propeller configuration and compared against experimental measurements. Results show that open-ended permeable surfaces substantially underpredict noise in the downstream region due to vortex leakage, whereas closed-end configurations significantly improve accuracy, with up to 97% of downstream microphones falling within 10 dB of experimental data (vs 33% for open-end). JetEnd correction provides only minor additional changes(less than 2.3 dB), indicating that spurious noise from end caps is small and largely confined to low frequencies. Both JetEnd and SPODEnd methods yield nearly identical predictions, confirming that a single end cap can predict sufficiently well. A simplified convective-spacing model is shown to align with dominant pressure-fluctuation structures extracted via Spectral Proper Orthogonal Decomposition, which means that, if correction is needed, JetEnd can be used. Limitations associated with smaller permeable surfaces highlight the need for future development of lateral boundary corrections to reduce contamination from side-edge vortex escape. While the findings are demonstrated on a specific case, the same physical reasoning suggests applicability to other propeller cases.