Experiment on clearance leakage flow and aerodynamic performance in shrouded turbine cascade

Flow structure at the exit of turbine cascades and aerodynamic performance were studied experimentally in a low speed wind tunnel for unshrouded and shrouded blades with a turning angle of 108.1°. The secondary structure, distribution of flow angles and total pressure loss coefficient on exit planes were investigated under various working conditions, including different clearances between the blade and the casing and different angles of incidence. Experimental results show that, compared with the unshrouded turbine cascades, the shroud can effectively control tip clearance leakage flow and reduce aerodynamic loss of cascade. With the growing clearance between the shroud and casing, the amount of leaked fluid increases. Consequently the mixing loss induced by the leaked fluid becomes larger. For the cascade studied hereto, the clearance should be less than 1% span of the blade. Variation of angle of incidence influences three-dimensional vortex structures and their intensity in cascade passages. Also it clearly affects static pressure distribution on the suction surface of the blade. Proper and positive angle of incidence helps improve the flow field, thus enhancing aerodynamics performance for cascades with large turning angles.