Comparison of Sweeping Jet Actuators with Different Flow-Control Techniques for Flow-Separation Control

Abstract

Flow-separation control on an adverse-pressure-gradient ramp model was investigated using various flow-control methods in the NASA Langley Research Center’s 15 in. wind tunnel. Sweeping jet actuators were compared to more classic flow-control techniques such as microvortex generators, steady blowing, and steady and unsteady vortex-generating jets. Surface pressure measurements and an improved oilflow visualization technique were used to characterize the effectiveness of these flow-control techniques in this research. The results showed that the vortex-generating jet using circular round orifices provided similar performance to the oscillating jets, which was mainly attributed to the larger skew angle of the circular round orifices compared to the current sweeping jet actuator configuration. However, a more direct comparison was made possible by operating the sweeping jet actuators in three different modes to produce steady-straight, steady-angled, and unsteady-oscillating jets. It was found that the steady-straight jet was the least effective method for a fixed momentum coefficient. The steady-angled jet achieved better control performance than the steady-straight jet, which was attributed to the generation of streamwise vortices that energized the boundary layer by mixing high-momentum fluid with near-wall low-momentum fluid. The unsteady-oscillating jet achieved the best performance by increasing the pressure recovery and reducing the downstream flow separation.