Low-Fidelity Methodology for Rotor Tonal Noise Prediction During Angular Velocity Transients

This work presents a low-fidelity framework for rotor tonal noise prediction during transient variations of rotor angular velocity, developed with the aim of enabling fast and accurate aeroacoustic analyses for electric vertical takeoff and landing vehicles, characterized by distributed-propulsion systems. The approach couples the vortex particle aerodynamic solver FLOWUnsteady with a time domain acoustic solver based on Farassat’s 1A formulation of the Ffowcs-Williams and Hawkings equation. The methodology is validated against high-fidelity Lattice–Boltzmann simulations for a two-bladed propeller operating under steady and time-varying angular velocity conditions. The results show that the low-fidelity model accurately computes the aerodynamic loads and tonal noise characteristics predicted by the high-fidelity solver, while requiring orders of magnitude less computational time. During an angular velocity variation, the sound pressure level change is governed by the time-variation of the rotor angular velocity, reaching its maximum where the time derivative of the rotor angular velocity peaks. A low-frequency component emerges along the rotor axis, associated with the axial loading and mean pressure variation induced by thrust changes. The proposed framework demonstrates strong potential for fast noise prediction in transient operating conditions, offering a valuable tool for preliminary design and perception oriented studies for advanced air mobility applications.