Re-orienting the Flow over an Inclined Cylinder of Finite Aspect Ratio

Abstract

Flow around an inclined and yawed circular cylinder of finite aspect ratio, that was either swept back or swept forward, was investigated experimentally. The cylinder was capped by an ellipsoid of revolution to maintain symmetry with azimuthal rotation. Circumferential and spanwise tripping was deemed to be necessary after preliminary investigations, and thus the flow was rendered turbulent. The cylinder housed two small actuators (dividing the cylinder in three parts) emitting sweeping-jets tangentially to the surface, and orthogonally to the axis of the cylinder. Actuation created large yawing moments capable of overcoming the natural restoring moment toward the plane of symmetry, by creating intended asymmetry in the near-wake. Thus, in the swept-back configuration this experiment is relevant to the control of an aerial refueling boom (the orientation and attitude control of a refueling boom thus avoiding the ‘H’ shape control surfaces that are currently used on Air Force tankers); while in the swept-forward configuration it enables the control of a cylindrical missile type object at large incidence angles. The forces and moments acting on the cylinder at various yaw angles were measured by balance while the preliminary interaction between the jets and the flow in the lee of the cylinder was mapped using 2D-Particle Image Velocimetry. Surface flow visualization was used in order to confirm the sensitivity of the flow to the azimuthal location of the actuators at different yaw angles. Employing a triad of experimental techniques is essential to investigate the interaction of active flow control on the nearby boundary layer and study its influence on the vorticial structures in the near-wake. Most of the experiments were carried out at Mach 0.12 or less and Reynolds number ~10^5.