The Influence of Lean and Sweep in a Low Pressure Steam Turbine: Analysis of Three Stages With a 3D CFD Model

The present paper accompanies the analysis of Vo¨lker et al. (2008), where experimental measurements on a three stage LP turbine for different configurations with lean and sweep in the last nozzle guide vane were presented followed by an analysis of these with a through-flow method. The present paper continues the analysis of the three stage machine with the support of steady 3D RANS calculations with stage interface (mixing) planes between the stages and making use of the SST turbulence model. The flow simulations are validated by comparison with flow traverses and with blade surface static pressure measurements. Good agreement is found between the simulations and the measurements, and the causes of discrepancies are analysed and discussed. In particular, the paper discusses the CFD results on two measured configurations focusing on the design mass flow and with regard to: • the effect of neglecting a backward facing step in the shroud contour above the rotor of one of the stages on the calculated flow-field; • the detailed changes in the spatial flow-field due to the introduction of sweep in the last nozzle row; • the prediction of the radial distributions of loss coefficients for the last two turbine blade rows; • the use of different models for the equation of state: an equilibrium or a non-equilibrium steam model.