Numerical Study Of Wet Steam Two Phase Condensation Flow In Turbine

In low pressure turbine stage, the presence of homogeneous condensation leads to problems of losses in turbine efficiency. Pressure distribution change caused by condensation and the interaction between nucleation and some sophiticate phenomenon would introduce some addition loss. Therefore, the research on wet steam flows is very important to the design of wet steam turbines.Numerical simulation of condensing flow was performed. An Eulerian/Eulerian model was developed for calculation of the wet steam flows with spontaneous conden-sation. The process of condensation was calculated by quadrature method of n order moments. The model of hetgeneous nucleation based on convex spherical substrate surface nucleation was performed. The numerical algorithm is established with the high resolution TVD scheme and the time-marching technique is adapted.A correction water droplet growth theory based on Langmuir-Maxwell model is introduced. In the initial stage of droplets growth, droplets are in the molecular regimes. And if droplets are larger than the mean free path, droplets are in the continuum regimes. But in low pressure turbine, droplets are almost in transition regimes between molecular regimes and continuum regimes. Accurate mathematical model is absent in the regimes. An equation for the mass transfer embracing continuum and molecular regimes is given. The droplet growth rate can be determined by simultaneous solve heat and mass transfer equation. Calculation is accurate in molecular regimes and continuum regimes and the transition region.Numerical simulation is performed for homogeneous condensation in wet steam two-phase flows in Laval nozzle and turbine cascade, good agreement was obtained between the numerical results and experimental data. Pressure rise and droplets distribution are showed in the result. Latent heat release in condensing flow would decrease the exit Mach number, change the flow angle and induce boundary layer separation. Shock wave would redistribute. Then additional loss would be caused. The character of heterogeneous flow is studied, condensation happened in low supercooling Particles in the steam have remarkable influence on condensing flow. The heterogeneous condensation leads to the removal of the pressure rise and approaches an equilibrium profile.The method of controlling condensation in cascade is introduced. It has been known that the nucleating and growth processes are sensitive to expansion rate. In nucleating flow, the suctionside blade profile line downstream of throat should be straight, and then the steam expands slowly, the strenth of boundary layer separation and wake votex can be reduced and the droplets distribution is uniform. The droplets number magnitude in wake can be reduced by reducing local expansion rate near trailing edge.In cascade, the outlet flow angle in condensing flow departures from the value designed by traditional single-phase design method. This leads to inducing additional aerodynamics losses and undesirable effects to the through-flow capacity of the cascade. With different inlet parameter, nucleation would occur in nozzle or moving blade, and the inlet flow angle of moving blade would change to different trend. In designing primary nucleation stage, the blade design should be on the base of flow condition.