Numerical Investigation of Nucleating Flows of Steam in a Cascade of Turbine (Effect of Overall Pressure Ratios)

In the course of expansion in turbines steam nucleates to become a two-phase mixture, the liquid consisting of a very large number of extremely small droplets carried by the vapor. Formation and subsequent behaviour of the liquid lowers the performance of turbine wet stages. The calculations were carried out assuming that the flow is two dimensional, compressible, turbulent and viscous. A classical homogenous nucleation model applied for the mass transfer in the transonic conditions. The aim of the present study is investigation of outlet pressure effect on second phase generation in a steam turbine. The maximum and minimum of droplet numbers have been achieved and nucleation zone has been specified in blade passage. Pressure profiles around the blades are compared with the experimental data and good agreement is observed. Results show that the most condensation is on the suction surface of blade and it grows by decreasing the downstream pressure.