Rotor blade cooling in high pressure turbines

A simplified model of a cooled turbine blade is used to illustrate the important features of cooling. Progress from early convection-cooled blades through to today's blades is traced with reference to the Spey and the RB 211 engines. Consideration of the internal cooling shows that where maximum cooling effectiveness is wanted the Stanton number/friction factor ratio is important. A modified Spalding and Patankar theory predicts the external heat flux in an uncooled static cascade, but empirical factors are needed when this theory is applied to engine film-cooled blades. Operational experience of the Spey HP turbine blade is discussed. A new directionally solidified multipass turbine blade has been designed and developed for the RB 211 offering performance, temperature, and life improvements. The optimization of cooling, aerodynamics, stress, and manufacture requirements plays a crucial part in the design of such a blade. Finally, several new material and process developments have recently appeared which together with cooling advances should insure continued improvements to future cooled blades.