Flow visualizations of unsteady flow field in the endwall region of a turbine cascade

Unsteady flow field in the endwall region of a turbine cascade was visualized using the hydrogen bubble technique.Within the cascade passage without radial clearance, the leading edge horse-shoe vortex plays an important role in the endwall flow. Flow mixing among the pressure-side horse-shoe vortex, the suction-side one, the endwall boundary layer and the suction surface boundary layer occurs periodically in the passage. Existence of radial clearance weakens rapidly the horse shoe vortex, and the leakage vortex is close to the suction surface. The periodical interaction among the leakage vortex, the suction surface boundary layer and the endwall boundary layer results in much more flow mixing and unsteadiness.