Dynamic 3-D vortex structure of the laminar separation bubble on SD7003 airfoil

Recent increasing interest in laminar separation bubble (LSB) is aroused by the development of the micro air vehicles (MAVs), which normally cruise in the Reynolds number range of 50,000-200,000. This paper studies the LSB over the SD 7003 airfoil at the angle of attack $\alpha $=4$^{\circ}$ and at \textit{Re}=60,000 using the time-resolved PIV technique. A Nd:Yag laser operated at 1000 Hz and a high speed CMOS camera was synchronized to capture the particle images with the full resolution of 1504 x 1128 pixels at 1000 fps. Measurements were carried out from two orthogonal views: in the stream-wise wall-normal plane and the quasi-surface-parallel plane. 3-D disturbance was observed to start even prior to the point of transition. Vortex shedding in transition near the reattachment region of the LSB was clearly identified in the span-wise wall-normal plane, with the dominant K-H frequency of around 10.7 Hz. And subsequent vortex evolution in the reattached turbulent boundary layer was found to be characterized by paired positive and negative vorticity packets transported downstream.