Development of piezoelectric actuators for active flow control

The development of piezoelectric actuators for active type flow control is discussed. The type of actuators considered consists of a single sheet of piezoceramic material bonded to the underside of a shim: a unimorph flap design. Existing theoretical beam models are extended to incorporate a linear strain distribution in the composite unimorph beam structure. This model is combined with an optimization scheme to design a flap that maximizes the tip deflection per unit voltage for a given bandwidth. The optimization model is then used to design a piezoelectric actuator. The model predictions compare favorably to measurements of the actuator frequency response function. A sample application to control of separated flow from a backward-facing step is also described, in which the actuator is installed at the origin of the free shear layer. Detailed hot-wire measurements, together with dimensional analysis, reveal the physical mechanism responsible for the fluid-structure 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 the actuator.