The Structure of the Flow Behind the Last Stage of Steam Turbine at the Low Flow Rate Operating Conditions

Abstract

Introduction. The results of experimental studies, which given in various scholarly research sources, have shown that changes in the flow structure and the formation of a breakaway near a bushing (with a decrease in power) begins in the outlet nozzle and gradually spreads towards the last stage of low-pressure cylinder. As a result, theefficiency of the low-pressure cylinder and the power unit decreases.Problem Statement. The data analysis has shown that recently powerful turbines often operate in off-design modes. This leads to changes in the flow structure (the appearance of the breakaway near a bushing and the vortex rotating in the inter-row clearance) and additional energy losses, especially in the flow path of low-pressu recylinder, leading to erosive wear of trailing edges of the working wheel due to the suction of wet steam from the condenser.Purpose. The purpose of this research is to consider the movement of the working medium behind the working wheel in the outlet nozzle of the low-pressure cylinder and to evaluate the development of the breakaway near a bushing in the axisymmetric setting under the low-flow conditions to obtain dependences that allow analyzing the operation of turbine stages with a large fanning and preventing the turbine operation under the low-flow rate conditions.Materials and Methods. The methods for mathematical modeling of the processes in the flowing part of the turbine under low-flow rate conditions have been chosen based on the experimental research of V.A. Khaimov.Results. The characteristics of the interaction of rotor blades with the breakaway near a bushing have been given. The dependences that enable determining the characteristics of the flow behind the working wheel when it flows out into the outlet nozzle have been obtained.Conclusions. The proposed analytical methodology allows the use of a rational approach to the operation under the low-flow rate conditions and the prevention of erosion wear of working blades trailing edges of the laststages of low-pressure cylinder.