Off-Design Performance of a Single-Stage Transonic Turbine

This paper presents results of rig testing of a transonic, single-stage turbine at off-design conditions. Mapping of the 3.4 pressure ratio, 1.9 stage loading turbine ranged from 70 through 120 percent of design speed and 75 to 125 percent of design pressure ratio. Results show expansion efficiency dropping over 4 percent from 100 to 80 percent of design speed at design pressure ratio, while remaining within half a percent from 90 to 110 percent of design pressure ratio at design speed. Efficiency lapse rate from equivalent sea-level to cruise altitude Reynolds numbers at the design point was measured and found to be worth over 1.5 percent. Analyses of test results using a viscous three-dimensional solver showed very good agreement for the efficiency change with speed.