Electrokinetic Microactuator Arrays and System Architecture for Active Sublayer Control of Turbulent Boundary Layers

Results are presented from development of microactuator arrays that function on the electrokinetic principle to provide active control of streamwise sublayer vortical structures in turbulent boundary layers. The electrokinetic microactuator arrays induce volume displacements in the sublayer by electrokinetic pumping under an impulsively applied electric field. These microactuator arrays consist of individual microchannels formed in a substrate and filled with a 1-μm-scale doped porous polymer matrix that provides the required ζ-potential when wetted by the corresponding electrolyte. A system architecture is presented for large dense arrays of such microactuators that provides for greatly reduced control processing requirements within individual unit-cells containing a relatively small number of sensors and actuators. The resulting microactuator arrays have characteristics that make them potentially suited for practical sublayer control on full-scale aeronautical and hydronautical vehicles. Essentially loss-less frequency response of the electrokinetic microactuators has been demonstrated to 10 kHz. Several such microelectrokinetic actuator (MEKA) arrays have been fabricated from a basic three-layer design. A MEKA-5 full-scale hydronautical array, composed of 25,600 individual electrokinetic microactuators with 350-μm center-to-center spacings, arranged in a 40 × 40 pattern of unit-cells, each composed of a 4 × 4 matrix of actuators, was successfully fabricated in a 7 × 7 cm² tile in 250-μm-thick Mylar substrate material. Microelectromechanical system design and fabrication processes were used to produce a top layer for the MEKA-5 hydronautical-scale array. DC performance tests indicate that the MEKA-5 array achieves the required flow rates for active sublayer control on hydronautical vehicles with applied voltages of no more than 15-20 V.