Research on the performance improvement of a two-shaft gas turbine with a variable area nozzle power turbine

Both an increase in atmospheric temperature and a decrease in atmospheric pressure can lead to the degradation of the maximum allowable power output (MAPO) or the thermal efficiency of a gas turbine. In order to reduce these adverse effects, this paper provides a simulated study on the improvement of the MAPO and the variations of the thermal efficiency due to the fuel flow and variable area nozzle control under different atmospheric conditions. Simulation results indicate that the MAPO increases with the power turbine nozzle area, while the thermal efficiency shows a parabola trend. With the same increment of the power turbine nozzle area, the improvement of the MAPO goes up as the atmospheric temperature rises and the decrease of thermal efficiency is alleviated. Analyses show that the slow degradation of the compressor isentropic efficiency is a key factor that enables the MAPO to increase significantly and the thermal efficiency to remain almost constant.