Flowfield and Acoustic Measurements from a Model Tiltrotor in Hover

Abstract

Rotor ine ow aerodynamics and noise measurements were made on three cone gurations of an 8% scale model of the XV-15 tiltrotor in hover: 1 ) single isolated rotor, 2 ) two rotors with no fuselage, and 3 ) complete tiltrotor aircraft. For the tiltrotor aircraft cone guration and for the cone guration of two rotors without the fuselage, the mean ine ow velocity was higher at c = 270 deg compared with the rest of the rotor disk, leading to reduced blade angle of attack and blade loading in this region. This azimuthally varying blade loading caused an impulsive noise that radiated preferentially behind the model. For the complete tiltrotor cone guration, the turbulence ingested by the rotors was intermittent and depended on the instantaneous position of the fountain e ow, which shifted from side to side across the longitudinal plane of the model. The fountain turbulence had a higher velocity scale, smaller length scale, and was closer to isotropic than the ingested ambient turbulence. The tiltrotor cone guration radiated less harmonic noise, but more broadband noise than the cone guration with two rotors and no fuselage. Diagonal fences on the wings of the tiltrotor reduced the ine ow turbulence intensity in the fountain region by a factor of about 3, and reduced the noise by 4.1 dBA behind the model. Scaling relations were derived to extrapolate the model measurements to the full-scale XV-15.