Numerical investigation of the influence of the tip clearance flow and the Coriolis force on the near wal flow in a compressor stage

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Current efforts in turbomachinery to increase pressure ratio, reduce blade count, decrease the aspect ratio, intense part load operation, etc. lead to increasing influence of flows near the side walls on the overall engine performance. Especially the operating range, losses and heat transfer are influenced by these flows. The occurring mechanisms are not fully understood although being investigated since decades. Thus the current technological progress strongly requests adequate basic research activity. This deficit will be addressed by a joint research program of four research groups at TU Dresden, UniBw München und RU Bochum, by carefully coordinated simulations and experiments to produce relevant results. Beside the investigation of heat transfer and the development of methodical tools a major goal of this joint program is the detailed analysis of the effect of system rotation. Therefor a number of specially planed and adjusted configurations will be investigated and compared with each other.Within this consortium the purpose of the project at the Chair of Fluid Mechanics, TU Dresden, is twofold. One is to investigate the physics of the secondary flow near the side walls and to contrast it with the situation in a linear cascade. The other is to contribute to a reliable turbulence-resolving simulation technology for turbomachinery grids. The physical issues will be investigated with DNS and LES for configurations experimentally investigated in partner projects, thus insuring reliable validation. These involved and well controlled simulations can yield very rich data and, for example, provide information about transition processes. Simulating configurations with and without rotation will allow studying the dependence of the near-wall flow on inflow conditions and effects generated by the system rotation, such as Coriolis force, increasing pitch with blade height, radial pressure gradients, relative motion of the end walls and shear of the inlet boundary layer. The methodologically oriented part of the work are concerned with visualization and post-processing and predominantly with assessment and development of subgrid-scale models and wall models for LES. Indeed, there exists a large demand for improved models of this type well applicable to turbomachinery flows. The analysis of the simulation data obtained will be conducted with the project partners comparing results of different methods for the same configuration - like experiment, URANS, LES - or results for different configurations among which comparisons between compressor and turbine flow thus covering a very wide parameter range.