The effects of tip-clearance on the performance of nozzle blades of radial turbines. (2nd report Experiment and performance-prediction at three nozzle angles)

Abstract

In the preceeding paper a two-layer flow model was proposed for analyzing the influence of tip-clearance on the turning angle and the pressure loss of turbine nozzles, and the prediction was compared with a series of experiments at the rated nozzle angle. In the present experiment, the nozzle angle was changed so that the throat area was 0.8 and 1.4 times the rated condition and similar experiments were repeated. Contour maps of total pressure loss and spanwise distributions of mean exit-flow angle are presented. The theory based on the two-layer flow model predicts the effects of tip clearance well, although it slightly underestimates the clearance effect at a lightly loaded condition. The reason for that and a way to correct it are discussed.