On limitations of active stall control over a high-lift airfoil using synthetic jet technology

The effect of a synthetic jet on the flow past a high-lift YLSG 107 airfoil of 17% thickness was numerically investigated, and the main limitations of obtaining an efficient active stall control via synthetic jet were studied. The computational results using an Unsteady Reynolds-Averaged Navier-Stokes (URANS) flow solver were compared with the wind-tunnel experimental data, with a synthetic jet located at 17.5%c from the leading edge of the airfoil. The influences of momentum coefficient and jet angle on the stall performance were studied, which shows that two key limitations may lead to the fact that no remarkable improvement had been observed in the previous wind-tunnel experiment: 1) Momentum coefficient is too low. Only when momentum coefficient is larger than 0.001 can relatively evident improvement of the stall characteristic be obtained. With a momentum coefficient of 0.005, a non-dimensional frequency of 2.75 and a jet angle of 20°, the critical stall angle can be delayed by 2°, and the maximum lift can be increased by 8.7% (from 1.58 to 1.71); 2) The transverse synthetic jet used in the experiment is not suitable for the stall control over a high-lift thick airfoil. A near-tangent synthetic jet is more promising and strongly recommended for such type of flow.