Nagamany Thayalakhandan

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.Copyright

Inlet Guide Vane Failure: Aero-Mechanical and System Control Interaction Effect

The APU, a gas turbine engine is designed to provide the aircraft with electrical power and pneumatic air both on the ground and in-flight conditions. The variable inlet guide vane (VIGV) system is used to regulate the air flow to the load compressor. The vane motions are controlled by an actuator and associated linkage. Common failure mechanisms of the VIGV such as cracking, corrosion of vanes, have been reported. This paper discusses a particular mode of failure which involves the aero-mechanical and control feedback interaction. The failure phenomenon is characterized by sector and ring gear tooth non-uniform wear, jamming of sector gears, actuator resonance, actuator fluid contamination and subsequent engine shutdown. Solution to failure mode is also discussed.Copyright