Role of leading-edge vortex flows in prop-fan interaction noise

Abstract

An experimental investigation has been carried out to study the interaction mechanisms associated with wakes from unswept, aft-, and forward-swept vanes incident on rotating prop-fan blades. Wakes from a single, stationary upstream vane interacted with a single rotating prop-fan. Comprehensive flowfield and acoustic measurements were acquired over a range of takeoff operating conditions. The forward-swept vane caused the leading-edge vortex and a core velocity defect associated with it to move inboard towards the hub and away from the high-speed tip region of the prop-fan. The tip vortex had only a small axial velocity disturbance associated with it. This is in contrast to the aft-swept vane which directed the leading-edge vortex out towards the tip, and led a large axial velocity disturbance to be swept toward the prop-fan tip region. Noise measurements revealed that the forward-swept vane wakes generated relatively less interaction noise than the aft-swept vane wakes, at equivalent vane loadings. From this simulation study, a potential noise reduction strategy for the counter-rotating prop-fan is suggested which uses a forward-swept/ aft-swept counter-rotating prop-fan combination. By reducing the sweep or modifying the spanwise loading on the blades, it may be possible to control the magnitude and/or location of the velocity defect associated with the leading-edge vortex.