Shake-The-Box measurements of a laminar separation bubble on a SD7003 airfoil at low Reynolds number

This study investigates the behaviour of the laminar separation bubble (LSB) that forms on the suction side of an SD7003 airfoil under low Reynolds number conditions. A wide parametric range was explored, with three-dimensional flow measurements obtained using the double-pulse Shake-The-Box technique across Reynolds numbers from 30,000 to 80,000 and angles of attack between 4° and 12°. The main features of the LSB — including separation, transition, and reattachment points — were characterized and found to depend more strongly on the angle of attack than on the Reynolds number. Bubble length and thickness generally decreased with increasing Reynolds number and angle of attack, although adverse pressure gradients at high angles and low Reynolds numbers led to local increases. Transition and reattachment are observed to be closely associated with the development of Kelvin–Helmholtz (K–H) instabilities within the separated shear layer, which are accompanied by increased momentum exchange and flow recovery. The study also visualizes three-dimensional vortex structures, including roller-like formations and arch-like Λ -structures. These vortices were consistently observed across all tested conditions, and their spatial organization was captured in detail through volumetric measurements. The results provide insight into the dynamics of LSBs and contribute experimental data to improve understanding of laminar–turbulent transition in low-Reynolds-number flows. • Shake-The-Box measurements of LSB on an SD7003 airfoil at Re = 30k–80k. • Separation, transition and reattachment points characterized across angles of attack 4°–12°. • Kelvin–Helmholtz instabilities are associated with transition and reattachment processes. • Three-dimensional vortex structures are observed, including roller-like and arch-like formations.