Controlled axisymmetric body-wake coupling in a pitching motion

Abstract

The coupling between a pitching axisymmetric bluff body and its wake is modified in wind tunnel experiments using controlled interactions between fluidic actuators and the cross-flow over its aft end. The model trajectory is controlled using eight servo-controlled support wires with inline force transducers that are operated in closed loop with feedback from a motion analysis system which effects control authority of the wind tunnel model in all six degrees of freedom. The model dynamics studied in the present work is constrained to pitch. Actuation is effected by two integrated aft-facing synthetic jet actuators in the plane of the body pitch oscillation such that each actuator effects a time-dependent segment of local flow attachment over the aft surface. The present investigation focuses on the reciprocal relation between the response of the near and far wake to the actuation and the associated changes in the induced aerodynamic loads when the body executes nearly time-harmonic pitch over a range of reduced oscillation frequencies (up to k = 0.26) for ReD up to 2.3 × 105. The response of the wake to stabilizing and destabilizing actuations that effect reduction or enhancement of the aerodynamic loads is investigated using particle image velocimetry (PIV) and hotwire anemometry in the near and far wake, respectively. It is shown that the studied flow control approach induces aerodynamic loads that are comparable to the loads on the base flow pitching motions and therefore may be suitable for in-flight stabilization. The global unsteady aerodynamic loads on a pitching axisymmetric bluff body are controlled by modification of the coupling between the flow over body and its near wake using two synthetic jet actuators in the plane of motion on the body’s aft end. This actuation results in a time-dependent partial flow attachment of the nominally axisymmetric separating shear layer of the base flow over the aft end of the body, and the asymmetric changes have a profound effect on the evolution of the wake. These changes in the wake dynamics feed back to alter the global aerodynamic forces and moments, leading to about a 50% increase or decrease in the dynamic lift force or pitching moment, depending on the flow control strategy.