Turbojet Engine Investigation of Effect of Thermal Shock Induced by External Water-Spray Cooling on Turbine Blades of Five High-Temperature Alloys
NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS CLEVELAND OH LEWIS FLIGHT PROPULSION LAB
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The thermal-shock effect of water-spray impingement upon turbine rotor blades subjected to rated engine operating conditions was determined in an investigation of external water-spray cooling. A centrifugal-compressor engine, modified to permit water injection from orifices in the rotor blade bases and from stationary orifices in the stator, was employed. The engine was operated at rated speed 11,500 rpm and a turbine inlet-gas temperature of 1625 deg F. Turbine-blade cooling water was turned on and off in cycles which employed either sudden or gradual injection of cooling water. A total equivalent coolant-to-gas flow ratio of 0.032 through both the stationary and rotating injection system was maintained to provide uniform cooling over the entire turbine blade surface. The S-816 test blades withstood 40 cycles with sudden water injection without cracking while subjected to a centrifugal stress of 25,700 pounds per square inch at the blade root. Cracks along the blade trailing edges and in some cases along the leading edges appeared after 20 cycles with the Nimonic 80 blades, after 11 cycles with the Inconel X blades, and after 9 cycles with the HS-21 blades. The Guy alloy blades failed at the first application of water sprays. Gradual water injection did not improve thermal-shock test results.
- Jet and Gas Turbine Engines