REATTACHMENT STUDIES OF AN OSCILLATING AIRFOIL DYNAMIC STALL FLOWFIELD

The reattaching now over an oscillating airfoil executing large-amplitude sinusoidal motion around a mean angle of attack of 10 deg has been studied using the techniques of stroboscopic schlieren, two-component laser Doppler velocimetry, and point diffraction interferometry, for a freestream Mach number of 0.3 and a reduced frequency of 0.05. The results show that the dynamically stalled flow reattaches in a process that begins when the airfoil is very close to the static stall angle on its downward stroke and progresses over the airfoil through a large range of angles of attack as the airfoil angle decreases to about 6 deg. The airfoil suction peak shows a dramatic rise as the static stall angle is approached, and the velocity profiles develop such that the flow near the surface is accelerated. The process completes through the disappearance of a separation bubble that forms over the airfoil.