Numerical Modelling of Fluid-Structure Interaction in a Turbine Stage for 3D Viscous Flow in Nominal and Off- Design Regimes

In recent years there have been major developments in turbomachinery aeroelasticity methods. There are now greater possibilities to predict blade vibrations arising from self-excitation or inlet flow distortion. This is not only important with regard to aircraft compressor and fan blade rows, but also in the case of the last stages of steam and gas turbines working in highly loaded off-design conditions. In order to predict the unsteady pressure loads and aeroelastic behaviour of blades (including the computation of shock waves, shock/boundary layer interaction and boundary layer separation), complete Reynolds-averaged Navier-Stokes (RANS) equations are used in modelling complex and off-design cases of turbomachinery flows. In this paper the 3D RANS solver, including a modified Baldwin and Lomax algebraic eddy viscous turbulence model, is presented to calculate unsteady viscous flow through the turbine stage, while taking into account the blade oscillations but without the separating of outer excitation and unsteady effects caused by blade motion. The numerical method uses the second order by time and coordinates an explicit finite-volume Godunov’s type difference scheme and a moving H-O structured grid. The structure analysis uses the modal approach and a 3D finite element model of blade. To validate the numerical viscous code, the numerical calculation results were compared with the 11^th Standard Configuration measurements. Presented here are the numerical analysis results for the aeroelastic behaviour of a steam turbine last stage with 760 mm rotor blades in a nominal and an off-design regime.