Effect of Different Matching States of Both Nozzle Vane's Clearances on the Performance in a Variable Geometry Turbine

Up to now there is no design structure limiting the matching states of nozzle vane's clearances at both hub and shroud sides in a variable geometry turbine, so this research work was carried out by numerical simulation to evaluate the effect of different matching states of nozzle vane's clearances on the turbine performance and provide help for improving turbine performance at off-operation in the future. The results indicate that: for close condition, the difference in turbine efficiency indicated by numerical results among three matching states of vane's clearances reaches up to 4 percentage at least, and the flow loss change appears mainly in rotor section; the matching states of nozzle vane's clearances can change the location of separate vortex on suction side of rotor blade near leading edge due to the flow angle in the leakage of nozzle vane is lesser than that in free stream, resulting that flow loss in the rotor channel changes and then turbine performance is influenced.