Experimental Closed-Loop Flow Control of a von Karman Ogive at High Incidence

The asymmetric vortex regime of a von Karman ogive with a fineness ratio of 3.5 is experimentally studied at a Reynolds number of 156,000. The wake of an axisymmetric bluff body is an ideal candidate for active feedback flow control because minute fluidic disturbances and geometry perturbations near the tip of the ogive get amplified through the flow's convective instability. The resulting disturbance interacts with the quasi-steady vortex location and produces a deterministic port or starboard asymmetric vortex state (i.e., side force). Accurate control or manipulation of this asymmetric vortex state holds the potential for increased maneuverability and stability characteristics of slender flight vehicles. For implementation of an active feedback flow-control system, plasma actuators at the tip of the ogive are used as the flow effector, and surface-mounted pressure sensors are used to estimate the vortex configuration in real time. A linear time invariant model developed from open-loop experimental tests and a proportional-integral control law are used to close the loop in the experimental setting. Closed-loop experimentation shows the ability to arbitrarily track a side force set point while also suppressing low-frequency fluctuations. Thus, the adopted model-based feedback flow-control approach is validated experimentally for a complex, three-dimensional flow.