Development of piezoelectric actuators for active flow control

The development of piezoelectric actuators for active flow control is discu ssed. The type of actuators considered consists of a single sheet of piezoc eramic material bonded to the underside of a shim: a "unimorph" flap design . Existing theoretical beam models are extended to incorporate a linear str ain distribution in the composite unimorph beam structure. This model is co mbined with an optimization scheme to design a flap that maximizes the tip deflection per unit voltage for a given bandwidth. The optimization model i s then used to design a piezoelectric actuator. The model predictions compa re favorably to measurements of the actuator frequency response function. A sample application to control of separated flow from a backward-facing ste p is also described, in which the actuator is installed at the origin of th e free shear layer. Detailed hot-wire measurements, together with dimension al analysis, reveal the physical mechanism responsible For the fluid-struct ure coupling. A quasi-static model based on the solid-body displacement of the incoming shear layer accurately describes the peak streamwise velocity perturbations produced by the actuator. This model leads to a proportional relationship between the flap tip displacement, the incoming boundary-layer profile parameters, and the streamwise velocity fluctuations produced by t he actuator.