Performance evaluation of a two stage axial-flow turbine for two values of tip clearance

Abstract

An experimental investigation w a s made of a two-stage turbine designed to drive an alternator for a 10-kilowatt-shaft-output space power system.Performance results were obtained for the turbine operating with the rotor tip clearance of 0.031 inch (0.079 cm) recommended for preliminary hot operation of the turbine.These results are compared with the results obtained with the design tip clearance of 0.013 inch (0.033 cm).Tests were made with cold argon as the working fluid over a speed range from 0 to 120 percent of design equivalent speed and at pressure ratios ranging from 1.08 to 1. 55.The results of the investigation indicated that the static and total efficiencies (based on turbine-inlet and collector-exit conditions) were 0.785 and 0. 792, respectively, for a tip clearance of 0.031 inch (0.079 cm).c r e a s e in turbine efficiency when the tip clearance is increased.This decrease in efficiency may be attributed to such factors as rotor blade tip unloading, increased throughflow over the blade tips in the clearance space, and the reduction of working blade area.The equivalent mass flow was 1. 2 percent greater, and the equivalent torque was 4 percent lower when the tip clearance was increased.designed with high rotor reaction, w a s very sensitive to changes in tip clearance.was a 3.7-percent decrease in turbine specific work for an increase in tip clearance of 1.0 percent of passage height.This decrease is substantially greater than the 1. 75percent decrease in turbine work obtained for a reference turbine of impulse design.These values represent a 4-percentage-point de-The results based on two tip clearances indicated that the subject turbine, which was There