Lattice-Boltzmann Simulations of Coaxial Rotors

Abstract

In the context of advanced air mobility vehicle development, the aeroacoustic behavior of compact coaxial rotor systems is investigated using lattice Boltzmann simulations performed with the ProLB solver. Eight hover configurations are considered, including open corotating rotors, open contra-rotating rotors, and SCRR, with variations in rotor–rotor separation distance and index angle. The numerical approach, based on direct noise simulation, is assessed against experimental measurements of aerodynamic performance, acoustic spectra, and noise directivities. Overall, the simulations reproduce the measured trends in thrust, torque, and total noise levels. The open corotating configuration with a zero index angle is found to be the quietest system because of reduced blade–vortex interactions and weaker unsteady blade loading. Introducing a 30° leading angle on the upstream rotor increases both tonal and broadband noise through enhanced blade–vortex interactions and partial flow detachment on the downstream rotor, without significant aerodynamic benefit. Open contra-rotating rotors provide the highest thrust but generate stronger tonal noise due to rotor–rotor interactions. Finally, the shrouded contra-rotating configuration is the noisiest case, mainly because of increased broadband noise associated with tip-leakage flow and blade–wake interactions.