High-Bandwidth Pulsed Microactuators for High-Speed Flow Control

A systematic study on the design, development, and characterization of high-momentum, high-bandwidth microactuators for high-speed flow control is described in this paper. Beginning with building-block experiments, multiple resonant flow phenomena are used in the actuator design to arrive at an actuator configuration that provides the desired flow properties. The first-generation actuator design consists of an underexpanded source jet incident upon a cavity. The lower surface of this cavity contains micronozzles through which the unsteady microjets (400 μm) issue. Results show that microjets produced by this actuator have a high mean momentum (300―400 m/s) and a significant unsteady component (20―30% of the mean). Experiments were conducted over a large range of parameters in terms of cavity length, source jet nozzle pressure ratio, and impingement distance. The results unequivocally demonstrate the ability to vary the frequency and the amplitude of the mean and unsteady momentum of microjets issuing from this actuator. By varying the dimensions of the actuator by few hundred microns and/or source jet pressure by roughly 1 atm, one is able to vary the frequency rather precisely over a range of 5―20 kHz. A correlation based on Strouhal number and jet column length is suggested for the design of actuators. Actuators in the frequency range of a few to well over 50 kHz have been designed and characterized. It is believed that the frequency range may be extended down to O(100 Hz) and up to O(100 kHz) using this actuator approach.