Study on Flow Fields in Variable Area Nozzle for Radial Turbine

The flow fields behind a variable area nozzle for a radial turbine were measured with 3-hole yaw probe and calculated with CFD. Two nozzle throat-areas were investigated. One was the smallest opening, and the other was the largest opening for the variable nozzle. The area ratio of the smallest to the largest was 0.27. Test results agreed with the calculated results qualitatively. The flow fields at minimum and maximum opening are presented and discussed. In case of the smallest opening, the leakage flow through the tip-clearance of nozzle vane influenced on the flow field downstream of the nozzle vane significantly. However the effect of leakage flow on the flow field downstream of the nozzle vane was very weak for the case of the largest opening. Extremely different flow fields were observed.