Turbine Pocket Blade: Structural Integrity and Tip Leakage Flow
The design of a turbine blade is a complex task involving the simultaneous optimization and compromise of different disciplines with the most important ones are aerodynamics and structures. Aerodynamics mainly involves optimizing blade profiles for minimum pressure loss while structures deals with fatigue and creep life. In small gas turbine application, the turbine pocket blade with aspect ratio less than unity is a typical case of such aero-mechanical optimization. The objective of this paper is to address two crucial topics encountered by such blade design configuration. They are (a) the integrity of the re-enforced pin and pocket fix-end wall under thermal cyclic loading resulting from combustor pattern factor and in combination with blade transient resonance and (b) the minimization of tip leakage flow to improve turbine efficiency. Finite element method and computational fluid dynamics are used to illustrate the blade pocket physical states and its underlying solutions. Structural analysis indicated that a bi-slotted pin is a suited solution to reduce loading of HCF nature at the blade wall-pin interface. Aerodynamic simulation showed that the pocket blade tip with scooped configuration reduced the tip leakage flow.