Partial Stall Effects on the Failure of an Axial Compressor Blade

Abstract

This paper is aimed to show the effects of partial stall on the fracture of the first stage rotating blades of the gas turbine compressors of an onshore gas refinery. The first part of the paper deals with the results of finite element modeling (FEM) of stress distribution and stress concentration areas on the blades under its first to third natural frequencies. Comparison of the stress concentration areas with the fractured blades shows that the blades have been fractured due to resonance under the first and second natural frequencies. The second part of the paper deals with the computational fluid dynamics (CFD) simulation of air flowing through the blades to determine the most probable sources of vibrational loads as the aerodynamic forces. Results of CFD simulations show that the operation of the gas turbines under 40–50% of their nominal output power—which has been very regular in the history of operation of the turbines—increases the possibility of stall at the tip side of the first stages rotating blades. The vortices shedding due to downwash flow at the tip side of the blades causes flow instability and increases the aerodynamic vibrational forces on the blades, which finally makes them to experience a kind of high cycle fatigue (HCF).