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An advanced flutter analysis of a final stage turbine row with a new 1.2 meter long shrouded blade is presented. The three-dimensional (3D) unsteady Reynolds Averaged Navier-Stokes (URANS) equations with the Spalart and Allmaras turbulence model were employed to model the flow. The flow entering the last stage is a mixture of saturated vapor and liquid. An equilibrium wet-steam equation of state was used to model the properties of the mixture. Multi-row steady state simulations of the upstream stator row, the turbine row and the extended exhaust section were performed. It was considered important to include the exhaust section in the steady-state simulations in order to accurately predict the pressure profile at the exit of the turbine. The flow simulations were relatively high resolution and the single passage turbine mesh had 798 208 cells. Linearized flow simulations for the turbine row were performed to determine the unsteady aerodynamic work on the blades for the possible aeroelastic modes. An exact 3D non-reflecting boundary condition (3D-NRBC) was applied at the inlet and outlet for the linearized flow simulations to eliminate non-physical reflections at these boundaries. The calculated logarithmic decrement values for the new turbine blade are compared with a reference case for a similar steam turbine blade at a condition known to have a long and safe working history. The new last stage was found to be more stable than the reference case at the flow condition examined.

Three-dimensional RANS-based numerical simulation of wet steam flow through last stage of a LP turbine has been performed. The stage geometry and flow conditions are defined in accordance with data of full-scale experiments on a LMZ steam turbine with power output of 1200 MW. Calculations have been carried out with the ANSYS CFX 12.1 package. Using the mixing-plane approach and the SST turbulence model, steady-state flows both in the nozzle and in the rotor blade channels are computed. Effects of blade deformation under the centrifugal force action are analyzed. Results of computations are compared with experimental data for outlet section flow parameters. The better agreement between computational and experimental data has been achieved when the blade deformation under centrifugal force action has been taken into account.

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