In order to further the understanding of turbine tip leakage and passage ∞ow mechanisms for undesirable entropy production, an experiment was conducted in a linear cascade at the Hessert Laboratory. Blade surface and tip endwall static pressure, total pressure loss, and wake vorticity measurements were taken to document the efiects of upstream axial Reynolds number, 1:0 £ 10 5 < Re2 < 5:0 £ 10 5 , and tip gap height, 0:015 < g=cx < 0:05 for ∞at and partial, suction-side squealer tip geometries, as well as active ∞ow control using a plasma actuator situated on the blade tip. Interaction of tip leakage and passage vortices proved critical, and an inverse relationship was observed between the two structures in terms of streamwise vorticity, core total pressure loss, and the vortex size denoted by the i‚2 criteria. When a squealer tip is added, the results indicate an efiective reduction in gap size, and thus a reduction in loss. However, the high loss region in the gap disappears, indicating that the squealer traps the air in the region. When a plasma actuator is used to control the ∞ow, the efiect depends strongly on the unsteady frequency at which it is run. An efiect is seen in the downstream loss, however the high loss region in the gap appears unafiected, indicating that this method does not trap air in the tip gap.