The Role of Vortices in Aeroacoustic Noise from Rotating Wings: Insights from Force and Acoustic Partitioning

Drones have several important applications such as wildlife monitoring, product delivery, security etc. but the noise they generate can be a major factor limiting their operation. The two main categories of drone aeroacoustic noise are tonal noise and broadband noise. This noise is generated due to periodic variation in aerodynamic force, blade vortex interaction, blade gust interaction, boundary layer-trailing edge interaction, stall and flow separation noise. Determining the relative importance of these various mechanisms is difficult since the surface pressure variations that are the source for this noise, are induced simultaneously by all these mechanisms. Vortex-induced pressure fluctuations are particularly important, but the vorticity field in these flows is highly complex, making it difficult to pinpoint the flow structures that are important for noise generation. We have used direct numerical simulations to simulate the flow associated with a canonical drone rotor and further used POD to decompose flow field into dominant modes. We then apply the recently developed force and FW-H based acoustic partitioning to examine the role of different dominant flow structures on the blade loading noise.