A numerical study of flow pattern in a deteriorated gas turbine under real operating condition

A numerical study of aerodynamics in a deteriorated gas turbine was carried out. In the present study, a hybrid method of CFD simulation and heat balance analysis were used to estimate entire performance of the gas turbine cycle and local flow characteristics in the turbine section. Using this analysis method, flows in a deteriorated gas turbine were simulated under an operating condition, which was designated using the same procedure with that used in a real power plant. In our previous study, the degradation of the gas turbine performance due to blades deterioration had been observed. In the present study, flow patterns were observed and mechanisms underlying the degradation of the gas turbine performance were discussed in detail. Influences of two kinds of deterioration on flow patterns were examined: the first was thinning of nozzle guide vanes in the first stage and the second was increase of rotor tip gap in the first stage. The results showed that the deterioration of nozzle guide vanes leaded to decrease of the Mach number through the nozzle, and this leaded to increase of the turbine isentropic efficiency due to decrease of the friction loss. The increase in the rotor tip gap affected a loss generation of the following stage. Changes of flow patterns and its effects were discussed varying operating points of a gas turbine.