ANALYTICAL INVESTIGATION OF PERFORMANCE OF TWO-STAGE TURBINE OVER A RANGE OF RATIOS OF SPECIFICnHEATS FROM 1. 2 TO 12/3

摘要

The effect of the specific-heat ratio γ a overall turbine per-formance was investigated analytically. The turbine model used in the analysis was a two-stage impulse turbine designed for a research in-vestigation in a sodium-vapor facility. Turbine-performance characteristics were obtained for γ-values of 1.2, 1.4, 1.53, and 1+2/3. A performance map was obtained at each γ-value covering a range of pressure ratios for speeds of 40, 60, 80, 100, and 120 percent of design speed.nThe results of the anlysis indicated primarily that overall per¬formance was only slightly affected by the variation of γ. A secondary effect was noted, however, in that as y increased the velocities in the second-stage rotor increased and caused the turbine design point to lie closer to the limiting-loading point at the higher values of γ. This secondary effect caused the design-point efficiency to drop from 0.745 for γ-values of 1.2, 1.4, and 1.53 to 0.730 for a γ-value of 1+2/3. It was concluded from the results that in most cases the equivalence parameters (blade- to jet-speed ratio and ratio of blade speed to inlet critical velocity) would be adequate to correct from one oper¬ating fluid to another. In cases such as those encountered herein, however, in which the design point approaches the limiting loading con¬dition, a better blade-speed parameter was shown to be the ratio of blade speed to the average of the critical velocity at the turbine inlet and. the outlet.