Numerical Study On Two-phase Flows Of Steam Turbine Removing-humidity Stage

Steam turbine plays a dominant role in power generation industry in the world. In order to improve the efficiency and operation reliability of steam turbine, it's necessary to study the nonequilibrium-condensing wet-steam two-phase flows.The present dissertation gives a comprehensive review to several aspects concerning the nonequilibrium-condensing wet-steam two-phase flows such as experimental researches, numerical model and method, nucleation and droplet growth theories, etc. Achievements acquired in the past decades and problems expected to be solved in the future in this field are summarized. And then the present dissertation depicts the numerical model, nucleation and droplet growth theory and virial state equation of steam employed.Homogeneous nucleation wet-steam flows are studied in cascade cited from Bakhtar. Different characteristics are detected in the computational results among flows with supersonic, transonic and subsonic outflow respectively. Nucleation has finite influence on pressure surface in all operating situations. In all flows, superheat or nucleating, the pressure distributions on pressure surface are approximate, which are only related to geometrical shape of cascade. In flows with supersonic outflow the abundant latent heat released accompanied with instantaneous nucleation causes great increase in the pressure of throat on suction surface. In flow with transonic outflow Mach number distributions are very different between superheat and nucleation flow, and especially in the throat down from which superheat flow has strong normal shock wave while nucleation flow only much less pressure rise. In flow with subsonic outflow superheat and nucleation flow with the same pressure ratio has resembling cascade pressure distribution, even the same in passage. The effect of rapid condensation has been masked by the diffusion, and the diffusion dominates the pressure distribution here.On the basis of 2-D cascade computation, 3-D numerical simulation is carried out with the complex nucleation two-phase wet-steam flow in removing-humidity stage. To simplify the problem, inflow with dry saturated steam is assumed. Due to the low subsonic outflow of stator and rotor, expansion shows moderate through the whole passage. The steam flow in stator passage remains around saturation and the nucleation doesn't appear. But to rotor the situation is very different, in which the steam flow undergoes a strong expansion, far from...