Destruction of wall-bounded vortices using synthetic jet actuators

Abstract

We experimentally explore the effectiveness of a rectangular orifice synthetic jet actuator for wall-bounded vortex destruction. Vortex flows near a boundary often present unforeseen or undesired forcing on a neighboring surface due to the low pressure concentration within the vortex. Synthetic jets -- primarily used for separation control, enhanced mixing, and induced turbulence -- offer a unique strategy for vortex mitigation due to the unsteady flow at the region of the orifice disrupting the coherence of the oncoming flow. In a flat plate boundary layer, we test multiple jet orifice configurations, vortex lateral position relative to the orifice, and vortex sizes. We find that each jet was capable of reducing the incoming vortex rotational coherence up to 70%. This disruption led to pressure recovery within the vortex wake region. The velocity wake of the vortex was more persistent (most jets produced a wake of their own) though some cases were capable of accelerating the fluid while maintaining moderate rotation reduction and pressure recovery. These results indicate that synthetic jets have the potential to mitigate a near wall vortex structure, particularly in scenarios where the position and size of the vortex are known.

Figures (13)

• Figure 1: Schematic of the side and top view of the wind tunnel insert with variable vortex generator and synthetic jet positioning.
• Figure 2: Characterization of the vortex from the vortex generator including the velocity (a) and q-criterion (b) fields. Measurements made at $x/h_o=5$ downstream of a $l_\text{VG}/h_o = 20$ & $h_\text{VG}/h_o = 3.75$ vortex generator. The boundary layer height is referenced.
• Figure 3: Characterization of three of the synthetic jet orientations: (a) $\alpha = 90^\circ$ & $\beta = 0^\circ$, (b) $\alpha = 90^\circ$ & $\beta = 30^\circ$, and (c) $\alpha = 45^\circ$ & $\beta = 0^\circ$ at a blowing ratio of $C_b = 1.0$. Isosurfaces of the change in total velocity (i) and vortex structure via streamwise q-criterion (ii) are shown for each. Figures replicated from VanBurenOrientation.
• Figure 4: Impact of the synthetic jet on an upstream generated vortex, represented by q-criterion (i) and velocity (ii) fields, comparing the actuator being off (a) and turned on (b) measured at $x/h_o = 20$. The synthetic jet has orientation $\alpha = 90^\circ$ & $\beta = 30^\circ$ and blowing ratio $C_b = 1.3$, and the vortex generator with $l_\text{VG}/h_o = 20$ & $h_\text{VG}/h_o = 3.75$ in middle position.
• Figure 5: Downstream development of the vortex development with the actuator off (i) and on (ii) with measurements made at (a) $x/h_o= 5$, (b) $x/h_o= 10$, and (c) $x/h_o= 20$ downstream. The synthetic jet has orientation $\alpha = 90^\circ$ & $\beta = 30^\circ$ and blowing ratio $C_b = 1.3$, and the vortex generator with $l_\text{VG}/h_o = 20$ & $h_\text{VG}/h_o = 3.75$ in the middle position.