Tip Vortex Effects on Rotor Aeroacoustics via Hybrid Blade Element Momentum Theory–Free Vortex Wake Prediction

During rotor operation, wakes and tip vortices form and convect downstream, generating unsteady velocities on the blade surface, which act as significant noise sources. High-fidelity numerical simulations account for these effects but are computationally expensive, while the rapid predictions based on blade element momentum theory (BEMT) alone cannot capture the fluid mechanisms associated with tip vortex wakes. This paper presents a hybrid BEMT and free vortex wake (FVW) method to compute mean and unsteady flow variables on blade sections. The BEMT solver accommodates arbitrary flow directions, accounting for variations with the rotational phase angle, while the FVW models tip vortex dynamics with initial strength from BEMT computations. Unsteady airfoil theory is applied to compute time-varying loadings in inflight conditions, serving as noise sources for acoustic calculations. The method is validated with a benchmark rotor in hover and axial flow conditions, where wake correction alters thrust but has negligible noise impact. In inflight conditions, the FVW significantly improves prediction accuracy for blade passing frequency harmonics compared to BEMT alone. Near-field velocity and vortex structures also match high-fidelity simulations well. Application to a multirotor vehicle demonstrates the method’s potential for rapid and efficient noise estimation in low-altitude flight scenarios.