Active Flow Control of Dynamic Stall by Means of Continuous Jet Flow at Reynolds Number of 1 × 106

Abstract

We have studied the influence of a tangential blowing jet in dynamic stall of a NACA0012 airfoil at Reynolds number of 1 × 106, for active flow control (AFC) purposes. The airfoil was oscillating between angles of attack (AOA) of 5 and 25 deg about its quarter-chord with a sinusoidal motion. We have utilized computational fluid dynamics to investigate the impact of jet location and jet velocity ratio on the aerodynamic coefficients. We have placed the jet location upstream of the counter-clockwise (CCW) vortex which was formed during the upstroke motion near the leading-edge; we have also considered several other locations nearby to perform sensitivity analysis. Our results showed that placing the jet slot within a very small range upstream of the CCW vortex had tremendous effects on both lift and drag, such that maximum drag was reduced by 80%. There was another unique observation: placing the jet at separation point led to an inverse behavior of drag hysteresis curve in upstroke and downstroke motions. Drag in downstroke motion was significantly lower than upstroke motion, whereas in uncontrolled case the converse was true. Lift was significantly enhanced during both upstroke and downstroke motions. By investigating the pressure coefficients, it was found that flow control had altered the distribution of pressure over the airfoil upper surface. It caused a reduction in pressure difference between upper and lower surfaces in the rear part, while substantially increased pressure difference in the front part of the airfoil.

Effects of the hinge position and suction on flow separation and aerodynamic performance of the NACA 0012 airfoil

“…A low free-stream turbulence level was applied to match the wind tunnel characteristics, so the stream turbulence intensity was selected as less than 0.1% [19,30]. Also, the SIMPLE algorithm [19,22,[30][31][32][33][34] for pressure-velocity coupling and upwind second-order method was employed to discretize the pressure, momentum and turbulence transport equations. A sufficiently time step of 1 × 10 −4 was used to achieve Courant-Friedrichs-Lewy (CFL) number lower than 1, and the results were converged when the scaled residual was less than 1 × 10 −6 .…”

“…Passive control devices are those which are not energy consumptive such as trailing-edge flaps [14][15][16] and leadingedge slats [17,18]. In contrast, active control devices are energy consumptives such as a small energy input by suction and blowing jets [19][20][21][22][23].…”

Comparative study of flow separation control using suction and blowing over an airfoil with/without flap

“…A low free-stream turbulence level was used to match the wind tunnel characteristics, so the stream turbulence intensity was selected as less than 0.1%. In addition, SIMPLE coupled algorithm [23,26,42,43] was applied for pressure-velocity coupling and upwind second-order method was employed to discretize the governing equations. A sufficiently time step of 1910 -4 were used to achieve Courant-Friedrichs-Lewy (CFL) number lower than 1 and the results converged when the scaled residual is less than 1910 -6 .…”

“…In the present study, the Unsteady Reynolds-Averaged Navier-Stokes equations were solved with the shear stress transport (SST) k-x turbulence model [32] adopted to simulate the boundary layer turbulence. SST k-x turbulence model provides excellent predictive capability for flows with separation [32][33][34][35] as mentioned in previous studies of similar flows [23,26,36]. This model includes both k-x and k-e standard models, which improves the calculations of boundary layer flows with separation and removes the sensitivity of the k-x model for external flows.…”

“…Their results showed that suction control can decrease the velocity gradient of the boundary layer, delay the transition and prevent generating the separation bubble. Tadjfar and Asgari [26] investigated the influence of a tangential blowing jet in the dynamic stall of the NACA 0012 airfoil. They concluded that placing the jet slot within a very small range upstream of the counter-clockwise (CCW) vortex had tremendous effects on both lift and drag coefficients.…”