Microactuator arrays for sublayer control in turbulent boundary layers using the electrokinetic principle

Control principles and microactuator arrays are described for drag reduction in turbulent boundary layers by manipulation of streamwise sublayer vertical structures. The microactuators described here are fundamentally different from traditional MEMS approaches. They have no moving parts, and induce volume displacements of the sublayer vortices by means of electrokinetic pumping under a time-varying applied voltage. Such electrokinetic microactuators have characteristics making them potentially suited for practical sublayer control on real vehicles. Theoretical frequency response of such eiectrokinetic microactuators is in the MHz range: actual microactuators have been fabricated and tested to frequencies as high as 20 kHz and shown essentially no AC performance losses. A basic three-layer design for such electrokinetic microactuator arrays has been developed, and several generations of microactuator arrays have been fabricated. Current fabrication is based on laser drilling of electrokinetic channels in plastic substrates with traditional metallization processes for the electrodes and leadouts. A porous polymer matrix is used for the electrokinetic channels. Two types of microactuator arrays are described; "point" actuators for active control with colocated sensors and processing, and "slot" actuators for passive control based on the "oscillating wall" approach, for which no local sensors or processing are required.