Download reduction on a wing-rotor configuration

This thesis studies the flowfield between a rotor and wing, a basic representation of aerodynamic interactions such as occur in the tiltrotor transition phase and low-speed forward flight. On tiltrotors in such regimes, the rotors of the craft operate above the lifting wings, creating continual interaction between the rotor wake and wings, producing download. Reducing the download-to-thrust ratio can yield benefits such as increased payload capability. The thesis also explores different methods of controlling the flow in a rotor-wing setup, with the aim to reduce the download on the wing from the rotor wake interaction. The effect of surface blowing through use of a tangential jet on the download is studied, as well as the effect of small trailing edge flap deflections.; Flow visualization shows an expected variation in vortex trails from the two rotor blades, with flap deflection increasing the divergence between these trails. The spanwise flow that forms the fountain effect was captured using Third Velocity Component solver results from Spatial Correlation Velocimetry velocity fields. The spanwise flow develops immediately on the wing at the leading edge, increasing downstream. Velocity field and unsteady pressure measurements showed a one-per-revolution variation of the flowfield superimposed on the expected twice-per-revolution fluctuations.; The static deflection of trailing edge flaps at small angles is seen to shift the rotor wake impingement area on the wing to the retreating blade side of the wing and reduce the magnitude of the pressures. A decrease in velocity magnitudes was shown, indicating a possible decrease in the spanwise flow. These reduced spanwise velocities on the retreating blade side skew the wake towards the advancing blade side of the wing. This behavior is also seen through unsteady pressure measurements and mean pressures. Slotted blowing on the retreating blade side of the wing demonstrated effectiveness at download reduction in hover. It also served to increase the effectiveness of small angle flap deflection in download reduction. Off-site tests reveal on upflow region above the rotor disk after blade passage. This upflow is attributed to blade passage effect, where the pressure wave from the rotor blade reflects off the surface of the wing beneath.