An overset grid method for large eddy simulation of turbomachinery stages

A coupling method based on the overset grid approach has been successfully developed to couple multi-copies of a massively-parallel unstructured compressible LES solver AVBP for turbomachinery applications. As proper LES predictions require minimizing artificial dissipation as well as dispersion of turbulent structures, the numerical treatment of the moving interface between stationary and rotating components has been thoroughly tested on cases involving acoustical wave propagation, vortex propagation through a translating interface and a cylinder wake through a rotating interface. Convergence and stability of the coupled schemes show that a minimum number of overlapping points are required for a given scheme. The current accuracy limitation is locally given by the interpolation scheme at the interface, but with a limited and localized error. For rotor-stator type applications, the moving interface only introduces a spurious weak tone at the rotational frequency provided the latter is correctly sampled. The approach has then been applied to the QinetiQ MT1 high-pressure transonic experimental turbine to illustrate the potential of rotor/stator LES in complex, high Reynolds-number industrial turbomachinery configurations. Both wave propagation and generation are considered. Mean LES statistics agree well with experimental data and bring improvement over previous RANS or URANS results.