Compact, high-power synthetic jet actuators for flow separation control

Abstract

Although strong potential of jets as flow separation control actuators has been demonstrated in the existing literature, there is a large gap between the actuators (SJA) used in laboratory demonstrations and the SJAs needed in realistic fullscale applications, in terms of compactness, weight, efficiency, control authority and power density. In most cases, the SJAs used in demonstrations are either too large or too weak for realistic applications. In this work, we present the development of compact, high-power actuators for realistic flow separation control applications and demonstrate the developed SJA technology in representative, flow separation control problems, including control of steady separation/stall. The developed actuators are compact enough to fit in the interior of a 14.75 chord, NACA0015 wing, have maximum power of 2.0 HP and can produce (for the tested conditions) exit velocities as high as 80 m/sec. Flow separation control was demonstrated over a 14.75 chord, NACA 0015 wing at angles of attack and free stream velocities as high as 25 degrees and 45 m/s, respectively and pressure data was acquired over the wing for a range of conditions. INTRODUCTION The separation of the boundary layer is associated with large energy losses, and in most applications adversely affects the aerodynamic loads in the form of lift loss and drag increase. Therefore, there is a strong incentive to delay or manipulate the occurrence of flow separation. For example, if the separation of the boundary layer formed over a bluff body is delayed, the pressure drag is greatly reduced; also separation delay will permit the operation of an airfoil/wing at higher angles of attack. Me Cormick (2000) showed that delay or elimination of separation * Research Assistant, Aerospace Engineering Department, Student Member AIAA. § Associate Professor, Aerospace Engineering Department, Member AIAA Copyright © 2000 by J. L. Gilarranz and O. K. Rediniotis. Published by the American Institute of Aeronautics and Astronautics, Inc. with permission. can increase the pressure recovery in a diffiiser. Hence, separation control is of great importance to most of the systems involving fluid flow, such as air, land or underwater vehicles, turbomachines, diffusers, etc. Many researchers have developed and tested methods of separation control in a variety of applications. Gad-el-Hak and Bushnell (1991) provide a comprehensive review on the research in the area of separation control previous to the year 1991. Typically the separation control techniques may be grouped in two categories: passive and active techniques. Most of the techniques, developed for passive separation control, may be found in the review by Gad-el-Hak and Bushnell (1991). Some of the parameters affecting the selection of a separation control technique include, but are not limited to: weight of system, power consumption (active type), power density, parasitic drag of device, size, reliability, cost and efficiency. Active separation control methods have included the application of: • steady boundary layer suction to remove the low momentum fluid. • wall heat transfer to control and modify the viscosity of the fluid. • moving walls in order to use the no-slip condition at the surface to energize the fluid close to the wall. • momentum addition to the boundary layer by steady blowing. • oscillatory blowing and suction. In the recent years the development of the socalled synthetic jet or zero mass flux devices and their potential for flow control has received a great amount of attention from the fluid dynamics community. This type of systems mostly involves small-scale, low-energy, typically high-frequency actuators, whose operation is based on the concentrated input of energy at high receptivity regions of the flowfield. They take advantage of the physical flow evolution processes to amplify the applied disturbance, which stands apart from the traditional brut force 1 American Institute of Aeronautics and Astronautics c)2001 American Institute of Aeronautics & Astronautics or Published with Permission of Author(s) and/or Author(s)' Sponsoring Organization.