The near-wake tip vortex flow structure behind a NACA 0015 airfoil with a trailing-edge flap was investigated. Lift-induced drag was computed based on vorticity and was compared with force-balance data. The vortex strength reached a maximum immediately behind the trailing edge and remained nearly constant up to two chord lengths downstream (x/c = 3). The displaced flap produced a more concentrated vortex of similar diameter and a higher induced drag compared to that of a baseline airfoil and had a larger radial gradient in circulation strength for flap angle δ < 15 deg; the vortex radius increased significantly for δ =2 0deg. For δ < ‐ 15 deg, the axial flow velocity was jetlike with the peak values increased with the flap angle. The nearly symmetric vortex was observed at x/c =2 .25 fo ra displaced flap while at x/c =1 . 5f or a baseline airfoil. The stength and interaction of the secondary and main vortices along the tip were also found to increase with the flap angle, and the vortex flow (immediately downstream of the deflected flap) was dominated by the presence of multiple vortices. The normalized circulation in the inner part of the symmetric vortex exhibited a self-similar structure, insensitive to the flap angle.