Performance Study Of Variable Conditions In Steam Turbine Last Stage And Inproved Design Of The Flow Passage

As the main machine of transforming heat into mechanical energy and electrical energy, steam turbine is an important energy conversion device. This paper presents performance analysis and structural improvements for the last stage of a 25 MW condensable steam turbine and improving its structure in ANSYS Workbench. The main contents and conclusions show as follows:1)For the defect of the original thermal design, thermodynamics calculations for the design condition and other six non-design conditions under its existing thermal parameters was conducted, which provides reference data for the simulation results;2) The difference between simulation results and experimental data of four-stages turbine is 4.22%, while the difference with design values is 2.74%,which verifies the correctness of computational model;3)By comparing the last stage's simulation results and the design data, the results show that exit static temperature agrees with the design value, but both stage isentropic efficiency and shaft power are larger than the design value. Through analyzing von-mises stress on different conditions, the results indicate that the blade's von-mises stress is much less than allowable stress, which meets the strength requirements.4) Through analyzing the isentropic efficiency, pressure coefficient, internal flow distribution and stress distribution, the effect factors of the.flow passage efficiency were achieved. And the flow structural has been improved with BladeGen and the effect of its improvement has been evaluated by aerodynamic performance and intensive property based on the results.The methods and results are as follows:a) The nozzle efficiency can increase 0.23% and the final stage isentropic efficiency can increase 0.067% by modifying the stator leading edge and trailing edge of the elliptic ratio;while the final stage isentropic efficiency increase about 0.23%;b) Through modifying the stator and rotor blade line, the final stage isentropic efficiency increases by 0.65% and 2.16% respectively; c) By improving the meanline angle to adjust the ratio between the stage, isentropic efficiency increases about 0.3%;d) The simulation results of five different meridian endwall of the stator show that horizontal meridian endwall can improve the nozzle efficiency and shaft power while the isentropic efficiency reduces;e) According to the simulation results, when the rotor number is 112,the shaft power can increase 9.4% and isentropic efficiency can increases 0.33%,while inlet mass flow and von-mises varied slightly..This article provides a new method for improving the cascade flow passage with BladeGen under ANSYS Workbench. This method can improve efficiency, shorten the research and development period and save cost obviously, which provides reference and basis for the development of modern turbine flow modification technology.