Effects of Reynolds Numbers on Wing Rock Induced by Forebody Vortices

Abstract

The wing rock induced by forebody vortices was investigated experimentally for a wing–body at high angles of attack, and the emphasis was put on the effects of Reynolds number on motion patterns. The results indicate that, if the boundary layers of the forebody exhibit laminar separation, the wing–body can regularly experience various motion types, as a tip perturbation changes its circumferential positions around the nose tip. After transition separation of boundary layers occurs, however, the effects of the tip perturbation on the motion types are alleviated progressively with increasing Reynolds number. Eventually, the wing-rock motions are independent on the tip perturbation, and the model always exhibits limit-cycle oscillations regardless of where the perturbation is located. In the case of fully turbulent separation, simulated by transition wires, the dominant roles of the tip perturbation on wing-rock types are recovered, in which the motion patterns of wing rock regularly vary with variation of the tip perturbation. Pressure distributions on the forebody and wings during a forced oscillation reveal that forebody and wing vortices apparently exhibit dynamic hysteresis. The associated flow mechanisms for sustaining the wing rock were analyzed based on static particle image velocimetry, and static- and dynamic-pressure measurements.