Thomas J. Lambert

Aerodynamic Control of Coupled Body-Wake Interactions

The unsteady interactions between fluidic actuators and the cross flow over the aft end of a moving bluff body are exploited for modification of the global unsteady aerodynamic loads in wind tunnel experiments using a moving axisymmetric model. The model moves in combined pitch and yaw which is designed to mimic the natural unstable motion of a similar airborne platform in the absence of roll. Actuation is effected using an azimuthallysegmented array of four aft-facing synthetic jet modules around the tail end of a model, and motion is effected by eight mounting wires that are attached to servo motors for timedependent, six degrees of freedom motion along a prescribed trajectory. Enhancement and suppression of stabilizing aerodynamic loads on the model are each investigated using coupled force and moment measurements and stereo particle image velocimetry in the near wake, at reduced frequencies of up to 0.26. The present measurements show significant suppression (up to 80%) and augmentation (up to 40%) of the platform’s motion-induced aerodynamic forces or moments with concomitant controlled deflection and decoupling of the near-wake from the motion of the body. The present investigations show that the effects of actuation on the near wake of the body are comparable to the effects of its baseline unstable pitch and yaw motion and therefore can be used to induce aerodynamic loads that cancel or enhance the baseline loads to effect dynamic steering and stabilization.

Unsteady Aerodynamic Loads Effected by Flow Control on a Moving Axisymmetric Bluff Body

The coupling between a moving axisymmetric bluff body and its wake is modified in wind tunnel experiments using controlled interactions between an azimuthal array of fluidic actuators and the cross flow over its aft end. Enhancement or suppression of the flow coupling has profound effects on the global unsteady aerodynamic loads on the moving body and the evolution of its near wake. The model moves in six degrees of freedom along a prescribed trajectory using eight servocontrolled support wires with inline force transducers that are operated in closed-loop with feedback from a motion analysis system. Actuation is effected by an integrated azimuthal array of four aft-facing synthetic jet actuators around the perimeter of the tail end such that each actuator effects a time-dependent segment of local flow attachment over the aft surface. The present investigation focuses attention on the reciprocal relation between the response of the nearand farwake 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). The response of the wake to stabilizing and destabilizing actuation programs that effect reduction or enhancement of the aerodynamic loads are investigated using particle image velocimetry (PIV) and hot wire anemometry in the near and far wake, respectively. It is shown that this flow control approach induces aerodynamic loads that are comparable to the loads on the baseline configuration, and therefore may be suitable for in-flight stabilization.