Advanced Flutter Analysis of a Long Shrouded Steam Turbine Blade

Abstract

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.

Influence of the Tip Clearance on the Aeroelastic Characteristics of a Last Stage Steam Turbine

“…The acoustic wave reflection from the outlet of the computational domain can influence the predicted aeroelastic stability of turbomachinery [13,14]. Fortunately, the acoustics wave was cut-off for the least unstable IBPA analyzed in this paper, and thus, the impact of acoustic reflection on the aeroelastic characteristic would not be critical with the extended fluid domain in the flutter test case.…”

Establishment of an open 3D steam turbine flutter test case

“…In this paper the flow is assumed to be as ideal gas with a ratio of specific heat of 1.12 and a dynamic viscosity of 1.032·10 −5 Pa·s, which is constant over the stage. It has been shown that this assumption is valid for steam turbine flutter calculations (Petrie-Repar et al, 2014).…”

“…In recent years, blade flutter risk has caught more attention because of the manufacturers interest to increase turbine output and improve performance level (Rice et.al, 2009). Three-dimensional unsteady inviscid (Masserey et.al, 2012 andRice et.al, 2009) and URANS (Stüer et.al, 2008 andPetrie-Repar et al, 2014) flow simulations for flutter analysis have been performed previously. However, the blade profiles and the flow properties presented by OEMs are always protected and kept as a secret.…”

Flutter Analysis of a Transonic Steam Turbine Blade with Frequency and Time-Domain Solvers

“…The test case was run with an ideal gas with the parameters listed in Table 1. For a justification of the use of ideal gas for the flutter analysis of steam turbines, the reader is referred to [22]. Table 1.…”