From the Blade Geometry to Prediction of Tonal Noise Component in Hover

Global interest in urban air mobility and small multi-rotor unmanned aerial systems is rapidly growing. Multi-rotors can fly in every direction, horizontally and vertically, and hover. However, the acoustic signature of these vehicles is of great concern. In the present study, the modelling of tonal noise components is implemented in a three-step approach. In the first and the second steps, the method requires modelling the steady and the unsteady components of aerodynamic loads, respectively. Steady aerodynamic loads are estimated with Blade Element Momentum Theory and XFOIL panel code, whereas the unsteady deterministic components are modelled with either Sears or Loewy functions. In the third step, the harmonic noise components are predicted. Aerodynamic loads and tonal noise components are modelled and compared with experiments conducted in the newly established anechoic chamber at the Faculty of Aerospace Engineering at the Technion-Israel Institute of Technology. The second and the third sound harmonics are predicted with high accuracy. The satisfactory agreement of thrust, torque and tonal noise results concerning the experimental measurements validated the proposed approach for predicting performances and noise radiation associated with low-Reynolds number propellers at the engineering level. The work can be seen as the infrastructure for rotor design.