Development and Characterization of Ultra-High Frequency Resonance-Enhanced Microjet Actuator

For flow control applications requiring very high frequency excitation, mechanical actuators often lack the durability or the control authority to be consistently useful in highspeed flows. High frequency excitation attempted in the past has been limited to either low frequency actuation with reasonable control authority or high frequency actuation with limited control authority due to limitation in frequency and amplitude of the actuators involved. In the present paper, an extension of previous development of the Resonance Enhanced Microjet actuators has been undertaken to extend the range of frequencies accessible beyond the range previously studied. Using lumped element model as well as empirical relationships developed in previous studies, two actuators have been designed with nominal frequencies of 25 kHz and 60 kHz. Extensive bench top characterization using acoustic measurements as well as optical diagnostics using a micro-schlieren setup was employed to characterize the frequency as well as amplitude of the actuator. The actuators performed at a range of frequencies 20.3-27.8 kHz and 54.8-78.2 kHz, respectively, as a function of NPR and impingement height. In addition to providing information on the actuator flow physics and the performance of the actuators with variations in operating conditions, the tests serve to develop an easy-to-integrate ultra-high frequency actuator for flow control in supersonic free shear and resonant flows.