Numerical Analysis And Mode Decomposition Of Flow In Axial Exhaust Hood Diffuser Of Steam Turbine

The exhaust hood is an important part of the steam turbine,which is located between the low pressure cylinder and the condenser of the steam turbine.The exhaust hood has two main functions: one function is to divert wet steam from the last stage of the steam turbine to the condenser;the other function is to reduce the speed of the wet steam and increase its static pressure to achieve the conversion of kinetic energy to pressure energy.Improving the performance of the exhaust hood can reduce the static pressure at the outlet of the last stage of the turbine,increase the enthalpy drop,and increase the capacity of the turbine to improve the efficiency.In this paper,the axial exhaust hood diffuser of a certain type of turbine is taken as the research object,the total pressure loss coefficient and the static pressure recovery coefficient are taken as evaluation indexes,and three types of influence factors on the performance of the diffuser are systematically analyzed by the numerical simulation method,including geometric parameters,such as diffusion,dimensionless length;aerodynamic parameters,such as diffuser inlet velocity distribution,Reynolds number;auxiliary structure effects,such as diffuser support structure,diffuser wall roughness.Finally,the dynamic mode decomposition method is used to decompose the flow field of the diffuser with specific geometric parameters,and the result shows: the vortex structures formed in the diffuser undergo generation,shedding,and diffusion.While the vortex moves in the axial direction,it generates a circumferential velocity due to the turbulent fluctuation,and there is a spatial coherence structure with a modal wave number of 3 and its multiple in the circumferential direction.In this paper,the flow characteristics and aerodynamic performance of the diffuser are analyzed from the aspects of aerodynamics and geometrical structures as well as unsteady modes,the conclusion of this paper helps to better understand the flow of the diffuser and provides a reference for the design of the axial exhaust hood diffuser.