Effects of Tip Clearance of Nozzle Vanes on Performance of Radial Turbine Rotor

Abstract

In radial turbines with variable nozzles, the flow downstream of the nozzles could be distorted by the leakage flow through the tip clearance of the upstream nozzle vanes. To investigate the effects of flow distortion on the performance of turbine rotors, two rotors with different numbers of blades were tested for three types of distorted velocity distribution at the rotor inlet. In the case of the 20-blade rotor with moderate blade loading, the flow distortion at the rotor inlet had a negligible effect on the rotor characteristics, and the measured data on the turbine performances agreed well with prediction. Predictions were made with a conventional one-dimensional flow model applied to the rotor flow, while a two-layer flow model was applied to the flow in the nozzle with clearance. In the case of the 10-blade rotor with heavy blade loading, however, the rotor performance was found to be sensitive to the inlet flow distortion and was considerably lower than the prediction.