Time Domain Flutter Simulations of a Steam Turbine StageUsing Sptectral 2D Non-Reflecting Boundary Conditions

In this paper, we show the application of spectral twodimensional non-reflecting boundary conditions (NRBC) in unsteady time domain simulations of three-dimensional turbomachinery flows. For this purpose, we conduct flutter simulations of a steam turbine stage and study the impact of the boundary condition formulation as well as of the boundary location on the prediction of aeroelastic properties. The main outcome is that spectral NRBC can be applied in challenging time domain simulations of realistic unsteady turbomachinery flows. Their reflection properties are shown to be superior to characeristic one-dimensional NRBC which significantly improves the prediction of aeroelastic quantities. In contrast to a prior implementation of spectral NRBC by the authors, convergence issues or a massive increase in computational costs, which would restrict the practical applicabilty of the spectral NRBC, do not occur.