Dynamic stall alleviation through mini-tabs

A mini-tab flow control device placed near the leading edge on a NACA 0012 airfoil was investigated for periodic plunging motion at geometric angles of attack 5, 9 and 15^o at a Reynolds number of 20,000. The dynamic measurements were conducted across a large range of amplitudes and frequencies to assess its performance as a peak lift and pitching moment suppressor. For low amplitude motion, the lift and pitching moment performance is largely dictated by the shear layer separated from the mini-tab, which does not roll up. For higher amplitude motion the performance is highly dependent on reduced frequency. Particle Image Velocimetry (PIV) revealed this dependency to be due to flow reattachment and vortex formation behind the mini-tab, which drastically reduced its effectiveness. Lastly it was shown that the range of beneficial lift suppression is closely linked with the Strouhal number based on amplitude, St_A, and the range of effective mini-tab lift reduction increases with geometric angle of attack. At the post-stall angle of attack, the mini-tab can delay the vortex roll-up over the airfoil to higher reduced frequencies.