This paper describes an experimental study conducted at the Advanced Aero Propulsion Laboratory (AAPL) on the design and development of actuator systems capable of producing high bandwidth, high momentum microjet arrays for active flow control applications. Using a simple geometry of a cavity with arrays of micro nozzles at the bottom end along with a primary source jet, highly unsteady microjets were produced in a frequency range of 6–60 kHz. The unsteady microjets, which are supersonic, have a mean velocity in the range of 300–400 m/sec with an unsteady component between 50–100 m/sec. Such actuators show considerable promise for flow control applications, especially in the supersonic domain. Notable characteristics of this design are its simplicity and the flexibility in controlling the frequency and amplitude suitable for the application of interest. The influence of feedback loop driven shear layer instability and other possible resonant mechanisms on the micro-actuator frequency response are outlined in the present paper. The location of cavity orifice within the Region of Instability (ROI), which is found to be the pressure recovery region of first shock cell of the source jet, plays a very important role in the output frequency and amplitude of the actuator. The length of the actuator cavity is another parameter that strongly influences the frequency of the actuator output. By using high resolution Micro-Schlieren images it was found that the frequency variation with Nozzle Pressure Ratio (NPR) is related to the shock cell properties of primary jet. As a result of this study, we have a better understanding of the geometric and flow parameters governing the unsteady properties of the actuator flow; an understanding that will be used to specifically tailor actuator design for various applications.

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