| Modern turbomachinery are moving in the direction of high parameters, high performance, high reliability, the research of the internal flow field caused researchers more and more attention, research methods and design tools originally established on a relatively steady flow of simplified assumptions already can not meet the requirements of higher performance indicators, so turbomachinery’s unsteadyphenomenon explore issues is already the trend.However,there are many factors can cause the unsteady flowphenomena.Iin this paper the author aimied at the unsteady phenomena caused by rotor-stator interference in last stage of a domestic150MW large steam turbine,then studied to explore the interaction mechanism,while did an analysis on the excitation phenomena which caused by unsteady flow. I wish the results can provide some support for desigh work ine the future.Collating information through a lot of reading literature, this article briefly describes the research and development status of unsteady flow in turbomachineryathome and abroad, then using the commercial softwarepackage called NUMECA for numerical simulation.First, do the steady numerical simulation for the last stage of turbine at design condition and analyze the flow field briefly, after that,do the unsteady numerical simulation based on the steady result which got earlier, combined with the unsteady flow field and the excitation spectrum to make a detailed analysis. The main conclusion are as follows:(1)Compared with the steady numerical simulation, the unsteady numerical simulation can describe the flow field in low pressure cylinder more accurate. The results of unsteady simulation at design point shows that the rotor-stator interaction is obvious and strong, this interference effect is directly responsible for the main reason of the variation of the load distribution of blade surface.(2)By analyzing the results, the upstream pressure vane potential field, the trailing edge and the shock wave of stators and such factors can cause the pressure fluctuation on the surface of rotor blades.(3)The unsteady isentropic efficiency of calculation is slightly lower than the efficiency while steady condition, and the efficiency is cyclical fluctuations over time. The result can conclude that the unsteady simulation could get more precise isentropic efficiency and provide better guidance for design work.(4)Examples in this article shows that the root of rotor blades suffer the unsteady aerodynamics most obviously and the unsteady characteristic of aerodynamics force on leaf is gradually weakened from root to top. Steam flow exciting force has the same situation, so the safe operation of the roots running condition has to be worried most.(5)A reasonable design of optimized airfoil and axial distance between stator and rotor, and through the rational organization of flow field conditions, can reduce the influence of unsteady effects caused by rotor-stator interference effectively, thus reduce the exciting force impact brings by unsteady flow.I hope that the results of article can provide reference for the research in related fields and design work in near future... |
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