Investigations on the coupling flow between full-scale last-stage steam turbine and low-pressure exhaust hood

Abstract

In a condensing steam turbine, the last-stage turbine and the condenser are connected by the low-pressure axial–radial exhaust hood. The exhaust hood has a complex geometry to make the flow change direction by 90°, while guiding the flow from the turbine to the condenser. During the operation, strong flow interactions between the turbine and the exhaust hood cause the flow pattern to become extremely complicated. The purpose of this paper is to investigate the coupling flow between the full-scale last-stage turbine and the low-pressure exhaust hood of a 600 MW steam turbine under actual operation conditions. The simulational calculations of the flow through the last stage turbine and the exhaust hood were realized by coupling calculations of turbine stage and exhaust hood in an external iterative manner. Equilibrium wet steam was selected as the flow medium. The coupling flow fields under different operation conditions were simulated and analyzed. It is found that the distributions of the turbine exit flow fields at different circumferential locations vary remarkably. The profiles of swirl angle and total pressure distributions at the turbine outlet change with the decrease of the mass flowrate, which further influence the flow behavior in the hood and lead to the reduction of the performance.