UC Davis

A physics-based broadband noise prediction approach is applied for small-scale drone rotors that have small chord lengths, low Reynolds numbers, and high rotational speeds. These unique characteristics, different from conventional full-scale rotors, are studied in the improved noise prediction models presented in this paper. The Roger and Moreau’s trailing-edge boundary condition and leading-edge back-scattering correction are included in the Amiet’s trailing-edge noise model in UCD-QuietFly. An incident field correction is proposed in this paper to account for the modified trailing-edge boundary condition. The laminar boundary layer-vortex shedding (LBL-VS) noise prediction is implemented in UCD-QuietFly using the semi-empirical Brooks-Pope-Marcolini (BPM) model. The theoretical predictions are validated against the experiments on three small-scale drone rotors in hovering and forward flights. LBL-VS noise is found to be an important noise source for untripped blades, but the BPM model requires an ad hoc tuning for good predictions. The effect of leading-edge back-scattering in broadband noise is found to be important for small-scale rotors at low frequencies when the reduced frequency (kc) is below 1.17. Finally, broadband noise is compared for different blade designs. At the same thrust, the ideally twisted rotor generates slightly higher broadband noise than the linearly twisted rotor, while the tapered blade tip is shown to reduce the broadband noise levels significantly.