15th European Conference on Turbomachinery Fluid dynamics & Thermodynamics

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Main Topic:

Radial Compressors



Anne-Lise Fiquet  - Ecole Centrale de Lyon, France
Jérôme Dombard - C.E.R.F.A.C.S., France
Nicolas Poujol - Safran Aircraft Engines, France
Pierre Duquesne - Ecole Centrale de Lyon, France


Even if significant flow separation zones occur in centrifugal compressors, they are able to provide high efficiency before reaching the stability limit. Numerical prediction of these separated zones is challenging in complex geometries such as compressors, in which turbulence modeling requires a special attention. Within the European project FLORA, a research transonic centrifugal compressor stage designed and manufactured by Safran Helicopter Engines is experimentally tested, and analyzed using numerical simulations. The compressor stage is composed of four blade rows: axial inlet guide vanes, a backswept splittered impeller, a splittered vane radial diffuser and axial outlet guide vanes. The compressor module is mounted on a 1MW test facility at the Laboratoire de Mécanique des Fluides et d’Acoustique, École Centrale de Lyon, France. Three different numerical approaches are used to conduct the numerical investigation, respectively steady and unsteady Reynolds-Averaged Navier-Stokes calculations with the code elsA, whereas high-fidelity simulations (LES) are performed with AVBP. Both RANS and URANS simulations are wall resolved whereas LES ones use wall-functions. Thanks to the natural azimuthal periodicity of the compressor stage, only one-third of the engine is computed in the unsteady simulations without any simplification of the geometry. After a brief description of the experimental methods and numerical approaches, the predictivity of the performance at high rotation speed given by the three numerical approaches is investigated. Then, flow field predicted by the simulations is analyzed in detail at the operating point near peak efficiency and at higher loaded conditions. Performance prediction shows discrepancies compared to experimentally measured performance. An overestimation of the pressure ratio and isentropic efficiency is observed based on RANS simulations and time-averaged LES simulations when URANS simulations predict an estimation close to the experiments. At higher loaded conditions, unsteady simulations develop an alternate flow separation pattern in the splittered radial diffuser. This phenomenon was also experimentally observed based on unsteady static pressure signals at different operating conditions. An in-deep analysis of numerical results will be addressed in the paper to understand the onset of the alternate flow separation pattern, which is highly relevant since it may trigger the surge or phase-lock with an acoustic mode of the experimental system, and affect the stability margin.


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