Loc Quang Duong

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

Understanding Blade Walking: Phenomenon and Mechanism

Blade walking or axial dislocation of a turbine blade along its fixings in the disk is a common and undesirable problem in turbomachinery since it eventually leads to the premature failure of the engine either due to rubbing of the rotor with the adjacent stator stages or due to the overload fracture of the disk fixings. The objective of this paper is to develop a clear understanding of the contributing factors and the mechanism behind the phenomenon of blade walking. Finite element method is used to illustrate the blade walking phenomena and its underlying mechanism.Copyright

An Approach on Bladed-Disc Tuning

High cycle fatigue of rotating components, produced as the system is driven near to resonant conditions, is undesirable and is one of the major design concerns in engineering today. Structurally, it is imperative to tune the excited vibration mode out of the operating speed range to avoid large amplitude vibrations. It has been demonstrated that for a single blade with distinct eigenvalues, it is possible to tune the eigenvalue of choice out of the operating speed range while maintaining little change to other natural frequencies through structural perturbations. These perturbations usually come in the form of a redistribution of the stiffness and/or mass [1]. The focus of this paper is to extend this approach to the tuning of two adjacent excited frequencies of a bladed-disc by first reducing the inter-blade coupling through stiffening the disc structure followed by “individual” blade tuning. Due to the complexity of the bladed disc structure, results from direct finite element analyses are used based upon analytical eigen-perturbed expressions to investigate the dynamic inter-blade behavior of an impeller. A good correlation between analysis and laser vibrometry test measurements is obtained.Copyright

An Approach on Tuning Frequency of a Rotating Blade

In a gas turbine engine, the forced vibration of a turbine blade under resonant conditions is undesirable and may lead to premature high cycle fatigue failure. From the aspect of structural integrity, this demonstrates that it is extremely important to tune the excited vibration mode out of the operating speed range. This leads to the question: Is it possible to perform structural perturbations, namely to the mass and stiffness, in such a way that only the eigenvalue of choice significantly changes — while causing little or no change in the other natural frequencies? This is focus of the present paper. Due to the complexity of the blade structure, it is difficult to obtain an analytical solution from the eigenvalue perturbation theory. Nevertheless, the derived analytical expressions provide guidance from which the finite element method may successfully be applied as an alternative approach. This tuning approach is validated experimentally.Copyright