A New Value to 3D Shape Optimisation of LP Turbine Stages Operating in Wet Steam

3D blading for the exit stage of a large power steam turbine was optimised based on direct constrained optimisation on coarse grids using a simplex method and a RANS solver with the Baldwin-Lomax turbulence model and state equation for perfect gas. The process of optimisation yielded new designs with changed 3D stacking lines of stator blades, including compound lean and sweep of stator blades. The results of optimisation are validated in this paper by 3D RANS computations on refined grids with the κ-ω SST turbulence model and perfect gas equation, or alternatively the real gas model without or with condensation. The paper concentrates on differences in flow fields and stage characteristics obtained from both gas models to estimate the quality of coarse-grid perfect-gas optimisation.