Research into vortex breakdown control

Vortex breakdown remains a significant and intriguing phenomenon that can have detrimental or beneficial effects, depending on the application. Thus there is a strong need to both better understand the phenomenon and to control it, either to prevent breakdown or to promote it. For the past 50 years, multiple flow control techniques have demonstrated the ability to manipulate the vortex breakdown location over slender delta wings at high angles of attack. An extensive historical review of these diverse control methods, mechanical and pneumatic, steady or periodic, is presented and discussed; however, none of these techniques has clearly demonstrated a superior efficiency or effectiveness in controlling either the vortical flow structure or the vortex breakdown location. Each technique, does, on the other hand, provide a unique approach to the control of the vortex breakdown depending on the desired outcome. There are still major obstacles to overcome before the control of vortex breakdown is implemented in flight. For example, oscillations of the vortex breakdown locations are difficult to quantify and to identify. The often poor effectiveness of control techniques can be in great part attributed to insufficient knowledge of breakdown and in an inability to accurately predict breakdown. When considering the large quantity of studies aimed at vortex breakdown control and their relative success, it is clear that decisive progress in this domain will require further basic investigations to clearly elucidate the physics of the phenomenon and to improve the predictive capability.