Flow Control of Vortical Structures and Vortex Breakdown over Slender Delta Wings

摘要

An understanding of vortical structures and vortex breakdown is essential for the development of highly maneuverable and high-angle-of-attack flight. This is primarily due to the physical limits these phenomena impose on aircraft and missiles in extreme flight conditions. Demands for more maneuverable and stealthy air vehicles have encouraged the development of new control concepts for separated flows. The goal of this paper is to describe experimental flow control techniques used to manipulate the vortical structures and vortex breakdown over slender delta wings at high angles of attack. The paper begins with a review of the experimental vortical flow control techniques implemented and tested over the past 50 years. Then it examines more closely two promising and different pneumatic flow control methods for the control of vortex breakdown over slender delta wings: open-loop, along-the-core blowing and periodic blowing, and suction along the leading edges. These studies were performed at Onera and at the U.S. Air Force Academy and consist of both experimental and computational analyses of subsonic flow fields around 70 degree delta wings over a broad range of angles of attack (20 degrees < alpha < 40 degrees) and root-chord Reynolds numbers (2 x 10(exp 5) < Re(sub c) < 2.6 x 10(exp 6)). Both flow control techniques have been shown to manipulate the vortex breakdown location over slender delta wings at high angles of attack. Each technique provides unique advantages for the control of the vortex breakdown location depending on the desired outcome. In addition to presenting these two distinct pneumatic flow control methods, this study has demonstrated the applicability of two powerful non-invasive diagnostic tools (Laser Doppler Velocimetry and Computational Fluid Dynamics) for evaluating and further understanding the complicated 3-D flow field. (23 figures, 61 refs.).