A Low-fidelity Framework for Propeller Noise Prediction

Due to the tightening of the regulations on emitted sound and pollution in civil aviation, new aircraft concepts were recently investigated. Well-known examples are electric Vertical Take-off and Landing (eVTOL), aircraft equipped with distributed propulsion systems, and drones. The increasing complexity of this new generation of aircraft makes the accurate prediction of the aerodynamics and aeroacoustics performance a more challenging task. Existing high-fidelity tools excel at predicting such performance, but they require a high computational cost and time. Moreover, the current low-fidelity tools often show limitations when applied to complex configurations such as the distributed propulsion systems. Then, the scientific community is looking for new tools able to support every step of the design process of the more quieter and sustainable aircraft. In this work, the numerical framework based on the Vortex Particle Method (VPM), FLOWUnsteady, was coupled with an in-house aeroacoustics solver using the Ffowc Williams-Hawkings analogy (FWH) for tonal noise and the Amiet approach for broadband noise. The solver was validated against high-fidelity numerical and experimental data, showing high accuracy with a low computational cost. Finally, the framework was used to investigate the interaction effect between adjacent propellers in different configurations. The aerodynamic solver exhibits high agreement with high-fidelity numerical and experimental data across a wide range of advance ratios (J) for all configurations considered. The aeroacoustic solver accurately predicts the first Blade Passing Frequency (BPF) for both isolated and distributed configurations with a low computational cost. The accuracy decreases for observer angles in upstream and downstream directions, but remains comparable to the high-fidelity data. Additionally, the distributed propulsion effects on the tonal noise and trailing edge noise were investigated. This work shows that FLOWUnsteady, coupled with the in-house aeroacoustic solver, provides a valid alternative to the conventional low-, mid-, and high-fidelity methods, achieving a high accuracy to computational cost ratio. In addition, the work showed that configurations with high aerodynamic interactions increase both tonal and broadband noise in the far field, highlighting the importance of using solvers able to capture unsteady aerodynamics from early stages of the design process.