LBM Simulations of Co-axial Rotors

In the context of developing new rotorcrafts dedicated to Advanced Air Mobility, aeroacoustic simulations of co-axial rotor systems have been conducted using the lattice Boltzmann method with the ProLB code. Eight configurations, spanning from co-rotating rotors to contra-rotating shrouded rotors, were analyzed in stationary conditions through comparisons with experimental data and flow field analysis. This investigation validates our numerical methodology, based on direct noise simulation, and enhances our understanding of noise generation and propagation of such propulsive systems. Our simulations successfully replicate all measured trends in global aerodynamic performance, average noise levels, and noise directivities. Maximum discrepancies were 1.5 N (9%) and 2.1 dB (averaged noise level on the considered microphones). Based on our analysis, the following observations have been made. The open co-rotating rotors is the quietest configuration due to reduced Blade-Vortex Interaction (BVI). A 30° leading rotor angle increases noise by inducing BVI and flow detachment on the downstream rotor. On the other hand, contra-rotation offers the best performance but generates high tonal noise. Finally, the shrouded configuration is the noisiest due to blade-flow interactions and detachments along the duct, resulting in reduced performance and additional noise sources primarily due to non-adapted blades and duct.