Post-stall flow control with upstream flags

Abstract The post-stall flow control using compliant flags of varying thickness and length, placed upstream a NACA0012 airfoil, was shown to be possible at an airfoil chord Reynolds number 100,000. flag wakes produced substantial increase in the stall angle maximum lift coefficient optimal cross-stream locations from wake centerline. Oscillating could generate periodic with better spanwise coherence than stationary bluff body. This resulted excitation, formation shedding leading-edge vortices periodically, providing mean enhancement. There is range mass ratio for which frequency coincides natural vortex instability or its subharmonic baseline wake. dimensionless function only, can predicted by reduced order model limit very large modified free-streamline theory separated flow. also frequency. Graphical abstract