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.
In the current study, the role of phase-difference between signals of two adjacent synthetic jet actuators (SJAs) in active control of flow over a rounded ramp geometry has been investigated. In order to accurately predict the separation and reattachment locations, wall-resolved large eddy simulation has been utilized to capture the locations of separation and reattachment. The two adjacent SJAs were placed upstream of the separation point. Six phase-differences between the two SJAs were considered, and two momentum coefficients were applied. First, the role of phase-difference in active flow control of a separation bubble behind a ramp-down region was investigated. Furthermore, the impact of an increased momentum ratio on the size and length of the separation zone was investigated to assess the effectiveness of phase-difference with respect to a higher velocity ratio. The effect of increased momentum ratio on the wall pressure fluctuations was also explored. As the second objective of this study, the flow and turbulent features were discussed to unveil the SJA actuation impact on the downstream flow. The time-averaged velocity and turbulent kinetic energy profiles and the turbulent production were examined and compared to the uncontrolled baseline case. It was found that a higher velocity ratio tremendously increased the turbulent energy before the separation point, while further downstream, the level of turbulent energy was uncoupled from the SJA momentum coefficient. Our study showed that by increasing the momentum ratio, the role of phase-difference in reducing the separation thickness lessened. Nevertheless, applying either a positive or a negative phase-difference of pi/2 still postponed the separation point.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.