Vortex Control for Low-Noise DEP Urban Aircraft

Suppression of noise from aircraft is a vital NASA goal, especially important for the vision of Urban Air Mobility. Small urban aircraft may utilize Distributed Electric Propulsion along with advanced structural and electric motor/storage technologies to achieve the necessary flight capability. However, these aircraft utilize propellers or fans to achieve the necessary thrust, with attendant community noise issues. We propose to suppress perceived noise, especially during takeoff and landing in urban areas, by limiting the formation of vortical structures near the propulsor tips and trailing edges. Tip vortices are common for airfoils, best illustrated by aircraft wings. The pressure difference between top and bottom creates a secondary flow, with a resulting vortex that increases noise and reduces lift. Winglets are effective in countering this effect. However, rotating airfoils – propellers and fans – cannot utilize winglets. Instead we propose to limit the secondary flow and tip vortex by utilizing thin, surface-mounted plasma actuators placed near the rotating blade tip. SurfPlasma Inc. is a world leader in plasma actuator technology, having developed boundary layer control devices for many applications, including technology effective in the control of high speed air flows, relevant to aircraft propulsors even at low vehicle speeds. Also demonstrated is a technique for providing the required voltage to rotating systems. The overall objective of the current project is to demonstrate feasibility of plasma actuator-based flow control in rotating systems in order to achieve significant suppression of rotor-induced noise, without loss of thrust. Development of this technology will benefit society by helping to enable more efficient intra-city personal transportation, with low infrastructure impact. Noise suppression technology would enhance acceptance of UAM vehicles and increase livability in urban areas and eventually impact larger aircraft and terrestrial fans. More »