Free-stream turbulence preceding high-pressure turbine blades has a crucial impact on blade fields including the heat transfer on the wall. Many parameters characterize this turbulence; its intensity, length scales and physical spectrum are addressed in the study of various operating points of the LS89 configuration. Usually, operating points where weak turbulence is injected are well predicted for all fields by Direct Numerical Simulations (DNS) and Large Eddy Simulations (LES). The MUR235 operating point however, with an experimentally injected turbulence level of 6%, remains incorrectly predicted when imposing the experimental values in the simulations. Such difficulties raise many questions amongst which mesh size and turbulent kinetic energy spectrum are of specific importance for LES. Going away from synthetic turbulence injection by imposing a physical energy spectrum can help improving the prediction of heat transfer. From the present study, it seems that turbulent spots developing in a pre-transition region for higher levels of turbulence on the suction side are important features to capture for proper predictions. In parallel, typical structures of boundary layers such as streamwise oriented vortices have been observed and their existence conditions the heat transfer field on the blade wall. From this specific study, all of these physical processes are seen to be highly dependent on the turbulent specification and turbulent transition observed for the MUR235 case. Depending on these inflow specifications, a transitional boundary layer may be encountered upstream of the shock thus modifying the heat transfer profile.

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The present study aims at evaluating the feasibility and the accuracy of the Large-Eddy Simulation of an actual high-pressure multistage compressor, performed with the TurboAVBP numerical method. TurboAVBP relies on the coupling of several domains via an overset grid method. The latter is demonstrated to keep the order of accuracy of the numerical scheme across six successive rotor-stator interfaces. The simulated configuration corresponds to the 3.5 stage axial compressor CREATE. Three unstructured grids of CREATE, with different resolutions, are generated. They contain 37 blades, the actual rotor tip clearances and a recirculating cavity. The predictions of the global aerodynamic performances and of the radial profiles are found to agree well with experimental data. The analysis of the flow shows that the finest grid exhibits the turbulent flow structures expected in such a configuration, including the blade and vane wakes and the rotor tip leakage vortices.

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Large-Eddy Simulation (LES) is recognized as a promising method for highfidelity flow predictions in turbomachinery applications. The presented approach consists of the coupling of several instances of the same LES unstructured solver through an overset grid method. A high-order interpolation, implemented within this coupling method, is introduced and evaluated on several test cases. It is shown to be third order accurate, to preserve the accuracy of various second and third order convective schemes and to ensure the continuity of di↵usive fluxes and subgrid scale tensors even in detrimental interface configurations. In this analysis, three types of spurious waves generated at the interface are identified. They are significantly reduced by the high-order interpolation at the interface. The latter having the same cost as the original lower order method, the high-order overset grid method appears as a promising alternative to be used in all the applications.

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This paper aims at evaluating Large Eddy Simulations (LES) for the prediction of the performance line and flow at off-design conditions in a multistage high-pressure compressor. A coarse and an intermediate grid are specifically investigated, since their associated computational cost appears affordable in an industrial context. Several operating conditions of the 3.5 stages high-pressure compressor CREATE are simulated, then results are compared to experimental data and to an existing URANS simulation. Both grids yield iso-speed performance lines close to experimental measurements, but only the intermediate one is able to correctly predict the experimental point at lowest mass flow rate. The unstable regime is specifically investigated in the last stage of the intermediate grid, showing the presence of rotating instabilities. Their amount and spinning velocity are similar to experimental observations and previous URANS results. Hence coarse LES appears as an interesting tradeoff for off-design predictions of flow in a multistage compressor.