Passive flow control of shock-induced dynamic stall via surface-based trapped vortex generators

Abstract

A novel passive approach for controlling the flow in a 2D dynamic stall at variabl freestream is investigated. 2D computational fluid dynamics simulations of an SC1095 airfoil with surface-based trapped vortex generator (STVG) type passive flow control were conducted. The airfoil was exposed to a fluctuating freestream of Mach 0.537 ± 0.205 and Re = 6.1 × 106 (based on the mean Mach number) and experienced a 10° ± 10° pitch oscillation with a frequency of 4.25 Hz. These conditions were selected as an approximation to the flow experienced by a UH-60A helicopter rotor airfoil section in an actual fast forward flight test case. The baseline simulations were cautiously validated with experimental data for both transonic flow and dynamic stall under the variable freestream. Then, 20 different local STVGs type geometry modifications were investigated as a means of passive flow control. Modifications were examined on both the airfoil’s upper and lower surfaces. Results showed that the STVGs were able to mitigate the negative effects of shock-induced dynamic stall. The best geometries could reduce the peak negative pitching moment by as much as 9–23% during the transonic phase of a cycle and by as much as 19–71% during the dynamic stall phase. Also, they were able to reduce peak drag by 8–20% in the transonic phase and by 15–44% in the dynamic stall phase. On the other hand, the lift-to-drag ratio was significantly increased by 3–28% per one rotor cycle. All the above advantages came at virtually no penalty in the lift.

Combined application of passive and active boundary layer aspiration in a transonic compressor rotor for shock wave/boundary layer interaction control

“…So far, a few SWBLI flow control methods have been developed and can generally be divided into passive and active groups. The former group usually includes placing bumps, 4–7 micro vortex generators, 8,9 and cavities 10–15 at some specific positions to adjust the local energy distribution in the flow field without importing any external energy. In the latter group, the boundary layer suction 16–20 and blowing 21,22 techniques are most common, which require extra energy expenditure to some degree.…”