PIV study of flow around unsteady airfoil with dynamic trailing-edge flap deflection

The flow around an oscillating NACA 0015 airfoil with prescheduled trailing-edge flap motion control was investigated by using particle image velocimetry (PIV). Aerodynamic load coefficients, obtained via surface pressure measurements, were also acquired to supplement the PIV results. The results demonstrate that upward flap deflections led to an improved negative peak pitching moment coefficient C (m,peak), mainly as a consequence of the increased suction pressure on the lower surface of the flap. The behavior of the leading-edge vortex (LEV) was largely unaffected. Its strength was, however, reduced slightly compared to that of the uncontrolled airfoil. No trailing-edge vortex was observed. For downward flap deflection, the strength of the LEV was found to be slightly increased. A favorable increase in C (l,max), as a consequence of downward flap-induced positive camber effects, accompanied by a detrimental increase in the nose-down C (m,peak), due to the large pressure increase on the lower surface of the flap, was also observed.