Experimental investigation of the tip-vortex interaction in UAV coaxial propeller system for noise generation

The present study introduces the initial steps of an analytical model designed to

estimate the tonal noise generated by coaxial contra-rotating propellers, with a particular

emphasis on their application in progressing technologies like drones and Urban Air Vehicles

(UAVs). The model can utilize empirical data as input, but the study highlights the value

of utilizing unsteady Reynolds-Averaged Navier-Stokes (uRANS) simulations to account for

the complex aerodynamic interactions inherent in contra-rotating systems. The main mechanisms

that have been identified in the literature can be categorized as potential or viscous

interactions. The potential interactions are related to the potential displacement of fluid due

to the blade passage, and the viscous interactions correspond to the wake and tip-vortex impingement

on the downstream blade. The study focuses the latter mechanism on a specific

test case employing two open propellers, and it considers the noise introduced by tip-vortex

interactions. The reliability of the model is evaluated by comparing its predictions with numerical

simulations and experimental data aimed at mapping the interaction region between

the two propellers.