The unsteady flow field near the endwall of a turbine cascade was visualized in a water tunnel using the hydrogen bubble technique. With the help of a light sheet, the experiment was carried out at different incidences without a radial clearance. A fluctuating horseshoe vortex system of varying number of vortices is observed near the leading-edge endwall. The pressure-side leg of the vortex moves toward the suction side after it enters the passage, while the suction-side leg develops along the corner of the suction surface. With the incidence increase, the pressure-side leg of the horseshoe vortex becomes stronger and can directly kick on the suction surface, causing a considerable influence nearby. The interaction and the flow mixing among the counter-rotating horseshoe legs, the endwall boundary layer and the main flow occur in the passage, forming a vortex system traditionally called the passage vortex. The vortex patterns and the interactions are related to the incidence angle.
Time Evolution of the Horseshoe Vortex System Forming around a Bridge Abutment