NUMERICAL INVESTIGATION OF WING ROCK PHENOMENON ON LOW ASPECT RATIO RECTANGULAR WINGS AT LOW REYNOLDS NUMBER

Abstract

Wing rock is a highly nonlinear complex phenomenon in which an aircraft undergoes self excited roll oscillations about its longitudinal axis, also known as Limit Cycle Oscillations (LCO). This phenomenon usually occurs at low flight speeds when an aircraft flies at higher angles of attack. Wing rock poses some serious challenges to stability, maneuverability and safety aspects of an aircraft. This study aims to investigate wing rock phenomenon on a rectangular wing of aspect ratio two and Reynolds number of 100,000. These conditions are typical of fixed-wing Micro Air Vehicle (MAV). The numerical study is conducted to find the static and dynamic stability derivatives in roll from 0˚ to 30˚ angle of attack, and a reduced frequency of 0.0346 through forced roll oscillations of 40˚ amplitude. The forced roll oscillations on the rectangular wing were implemented through the sliding mesh technique in a CFD solver. The loss in roll moment damping, a necessary condition of wing rock, was observed in the vicinity of the stall. The flow physics of the vortex dynamics revealed that the wing rock phenomenon starts to occur due to bursting of side tip vortex and its interaction with the leading edge separated vortex at an angle of attack near stall. The damping derivative in roll is approximated through cubic polynomial. This research work can be extended to locate the onset of wing rock phenomenon for a range of aspect ratios. Moreover, one can also dive into the other relating vortex induced vibrations phenomena.