On the perception of noise from a notional electric vertical take-off and landing (eVTOL) rotor in hover

Hover performance and acoustics of a 35% scale notional electric vertical take-off and landing rotor operating at moderate Reynolds numbers and Mach tip speeds below 0.4 is presented. Changes to blade count (2-bladed up to 5-bladed) are evaluated for the same blade shape and for a range of rotor collective pitch angles and rotor speeds. Increasing blade count generates substantial changes in thrust and torque at higher rotor collectives, whereas the 5-bladed rotor is only slightly more efficient than the 2-bladed rotor for the same changes in rotor collective. Changes to torque loads are also greater than changes to thrust gains as blade count increases. As for the sound field, all traditional source of noise (thickness-, loading-, and broadband-noise) are observed. When the sound field is scaled and then weighted (dBA) for human perception, the spatial topography reveals dipole-like behavior for all rotor operating conditions. A separation between tonal and broadband sources of perceived noise reveals how broadband noise is the dominant source of perceived noise for all blade number combinations at low rotor collective pitch angles. At higher rotor collectives, both tonal and broadband noise contribute equally to total perceived noise with the tonal noise contributing more for the 5-bladed rotor.