Characterization of a compact, high-power synthetic jet actuator for flow separation control

Abstract

This work presents the development and characterization of a new, high-power, compact actuator (SJA) for flow separation control. The developed actuator is compact enough to fit in the interior of a NACA0015 profiled wing with a chord of 0.375 m. Test bench experiments showed that the multipiston actuator array was capable of producing exit velocities of up to 90 m/s for an actuator frequency of 130 Hz and an actuator exit slot width of 2mm. The actuator was placed in a NACA 0015 wing and was tested in a wind tunnel. An experimental investigation into the effects of a actuator on the performance of the wing is described. Emphasis is placed on the capabilities of the actuator to control the separation of the flow over the wing at high angles of attack. The investigation included the use of force balance measurements, on-surface flow visualization with oil and tufts, off-surface flow visualizations with smoke, surface pressure distribution measurements and wake surveys. Most of the tests were performed at a freestream velocity of 35 m/s, corresponding to a Reynolds number of 8.96xl0. The angle of attack was varied from -2.0 to 29 degrees. In addition to flow separation control data, hot wire and pressure probe measurements at the exit of the actuator, are also presented. For the tests presented here, at angles of attack lower than 10 degrees the actuator tends to increase the lift curve slope as the actuation frequency is increased. At higher angles of attack, the SJA extends the range of angle of attack for which the wing may be operated without stalling. The use of the actuator causes an 80% increase in the value of maximum lift coefficient, and Post-Doctoral Research Associate, Aerospace Engineering Department, Member AIAA. * Post-Doctoral Research Associate, Aerospace Engineering Department, Member AIAA. § Associate Professor, Aerospace Engineering Department, Associate Fellow AIAA Copyright © 2002 by J. L. Gilarranz, L. W. Traub and O. K. Rediniotis. Published by the American Institute of Aeronautics and Astronautics, Inc. with permission. the angle at which stall occurs is increased from 12 to 18 degrees. The drag on the wing is decreased as a consequence of SJA actuation. This was verified with the force balance measurements and by analysis of the wake surveys. For angles of attack larger than 18 degrees, once massive stall has occurred over the wing, the operation of the SJA still provides a moderate amount of lift augmentation. At angles of attack larger than 25 degrees, a large frequency of actuation is required to produce any noticeable effects. INTRODUCTION In the recent years the development of the socalled synthetic jet or zero mass flux devices and their potential for flow control, especially separation control, mixing enhancement and fluidic thrust vectoring, has received a great amount of attention from the fluid dynamics community. They take advantage of the physical flow evolution processes to amplify the applied disturbance, which stands apart from the traditional brut force macro-scale control. Moreover, in terms of practical implementation, they offer significant benefits over oscillatory blowing techniques from an existing air supply. The latter technique requires supply lines that deliver the air from the supply source to the location of flow control. Even in fixed wing configurations, this increases the complexity, cost and weight of the overall system. In rotary wing flow control applications, for example rotating blade stall in helicopters (Greenblatt et al., 1998), the situation is evidently further complicated. In contrast, a actuator (SJA) can be a standalone unit installed at the location where the flow control is needed, requiring very little communication with hardware away from that site. In this case, the communication is mostly in the form of electrical power and signals. Furthermore, the SJA could be integrated with flow sensors, control circuitry and control algorithms that can all reside in the vicinity of the flow control site, further reducing the system's need to communicate with remote hardware. 1 American Institute of Aeronautics and Astronautics (c)2002 American Institute of Aeronautics & Astronautics or Published with Permission of Author(s) and/or Author(s)' Sponsoring Organization.