Investigation of aerodynamic effects of rotation on 6-DOF motion of flat square plate based on free flight experiments

Abstract

Plate-like debris is common windborne debris in windstorms. Although the 3-degree-of-freedom (3-DOF) motion (two translational DOFs and one rotational DOF) of flat plates has been widely investigated in previous studies, the 6-DOF motion is more likely to occur in real storms. We investigate the 6-DOF motion by performing free flight experiments of a square plate with different initial orientations under uniforms flow in a wind tunnel. Two cameras are used to record the flight motion of the plate. Then the recordings are processed in an image analysis software to estimate the kinematics of the plate. We first investigate the characteristics of the rotational motion. According to the rotational characteristics, the plate trajectories are categorized into four flight patterns: flutter, tumbling, transition, and quasi-translation. Then we explore the rotational effects on the aerodynamics. We propose a hypothesis that the magnitude and direction of the rotational forces depend on the angular velocity and the relative wind velocity. We also propose a hypothesis that the rotational moment has negligible influences on the direction of the instantaneous moment. These hypotheses are supported by the experimental results. These verified hypotheses may be helpful for modelling the aerodynamics of the 6-DOF motion of flat plates.