Investigation of Choking and Combustion Products' Swirling Frequency Effects on Gas Turbine Compressor Blade Fractures

Abstract

Premature fracture failure of blades occurred in four of a refinery's gas turbine compressors. In order to evaluate the probability of combustion instability's effects on failure of the blades; i.e., choking and chamber resonance problems, 3D models of the combustion chamber structure and combustion flow were studied with finite element and computation fluid dynamics codes, respectively. Comparison of results of combustion chamber natural frequencies with combustion swirl frequency showed that the chamber structure is not under resonance. In order to verify probability of choking, the combustion product flow's Mach number was studied. Results of the Mach number distribution showed that the flow is subsonic in the transition piece area but, due to existence of supersonic flow conditions near the swirl vanes it may become supersonic in some critical conditions. Thus, it is suggested to operators that, for avoiding choking probabilities, it is better that engine operation be maintained close to optimum design conditions. Results of simulations showed that the fracture of the blades is not due to combustion problems.