Experimental Results of a Transpiration-Cooled Turbine Operated in an Engine for 150 Hours at 2500 F Turbine Inlet Temperature

A key element in the development of gas turbine powerplants for advanced subsonic and supersonic aircraft is the ability to operate at turbine inlet temperatures significantly above the 1600–1800 F limit of today. This limit is imposed by the fact that current materials available for use in turbines exhibit inadequate strength and oxidation characteristics above 1600–1800 F. Certain metals such as molybdenum, chromium, tungsten and other high-melting-point alloys show good strength properties at temperatures far above which conventional super alloys are useful in turbines. However, these materials lack either the ductility or oxidation resistance necessary for turbine components. A means of realizing the gains possible by operating turbines at high turbine inlet temperatures is through cooling of the highly stressed turbine components. The necessity of reliable and efficient turbine operation for periods of long life in an environment of gas temperatures above the actual melting temperatures of the materials requires that effective means of cooling the blades be developed. The authors discuss the design of transpiration air cooled turbines as a means of operating engines at gas temperatures of 2500 F and higher, utilizing available turbine materials which are limited to metal temperatures between 1600 and 1800 F. The technique utilized in fabricating transpiration air cooled turbine blades is discussed. The results of operating a full-scale J65 engine, modified to incorporate a single-stage turbine fitted with transpiration air cooled blades, for 150 hr at 2500 F turbine inlet temperature are presented.