Development and control of vortices over a very low aspect-ratio wing

The vortical structures over a thin rectangular wing with a very low aspect ratio (AR) of 0.277 are investigated in a wind tunnel at an effective Reynolds number of 3 × 106 . The maximum lift of this thin wing is found at an angle of attack of 42◦ . The flow separates at the leading-edge and reattaches to the wing surface, forming a strong leading-edge vortex (LEV) which plays an important role on the total lift. The results show that the induced velocity of the tip vortex (TV) increases with the angle of attack, which helps reattach the separated flow and maintains the LEV. Turbulent mixing indicated by the high Reynolds stress can be observed near the leading-edge due to an intense interaction between the LEV and the TV. The reattachment point of the LEV moves upstream closer to the wing tip, however. When applying pitch-up motion, with pivots at mid-chord, the maximum lift angle is increased with an increase in the pitch rate, but the maximum lift coefficient is slightly reduced. The pitching motion also causes delay in the vortical development over the wing, which is increased with an increase in the pitch rate. The delay in the LEV development due to the pitching motion is nearly identical to that in the TV development, indicating that the dynamics of the LEV is strongly influenced by the TV, which is confirmed by particle image velocimetry measurements. Flow control of the tip vortices over a very low aspect-ratio wing is carried out using the dielectric-barrier-discharge plasma actuators. The results indicate a large change in the aerodynamic forces by plasma flow control, where the lift coefficient is increased by the blowing plasma actuator by 23%, and is reduced by the suction plasma actuator by 30%. The change of the drag coefficient is less than 10%. The blowing plasma moves the tip vortex outboard away from the wing tip, increasing the streamwise vorticity as well as the turbulence intensities and the Reynolds stress. With the suction plasma, the tip vortex is shifted inboard closer to the wing tip. Co-flowing with the tip vortex, the blowing plasma increases the tip vortex circulation, while it is reduced by the counter-flowing suction plasma