Interaction of a finite-span synthetic jet with a laminar boundary layer: Effect of jet orientation

The formation and evolution of a finite-span synthetic jet within a zero pressure gradient laminar boundary layer were analyzed utilizing Stereoscopic Particle Image Velocimetry (SPIV). The effect of the orifice orientation, including the pitch and skew angles, was studied at a free stream velocity of U_∞= 10 m/s and a fixed aspect ratio and blowing ratio of AR = 12 and BR = 1, respectively. Pitch angles of α = 20°, 45°, 65°, and 90° at a constant skew of β = 90°, and skew angles of β = 0° - 90°at a constant pitch of α = 90°every 15° were analyzed. The flow fields were analyzed with a focus on the effect of the jet on the flow field as well as the increased mixing of the flow. It was found that as pitch angle decreased, the added streamwise velocity increased due to the aligning of the synthetic jet with the free stream direction. Alternatively, an increase in pitch increased streamwise mixing because of the stronger induced streamwise vorticity. In addition, as the skew angle changed from being oriented perpendicular (β = 0°) to the flow field to parallel (β = 90°), the flow field was significantly affected. The perpendicular orientation yielded a vortex pair, which remained close to the wind tunnel floor, whereas for the parallel orientation the vortex pair advected away from the tunnel surface due to its own induced velocity. From this study, it is clear that the orifice orientation needs to be taken into consideration when applying a synthetic jet of finite-aspect ratio as a flow control device.