Highly efficient and concurrent flexible operation are heavy demands on state-of-the-art centrifugal compressor units. Diffuser end wall contouring is a measure to delay the incipience of instability and therefore to extend the compressor’s operating range while maintaining efficient performance. In the presented paper, a hub-side wall contouring, applied in the vaneless space upstream the diffuser’s leading edge and within the diffuser passage is examined. CFD calculations utilizing the nonlinear harmonic method are performed for both a baseline diffuser design with parallel channel walls and the hub-side wall contoured diffuser design. Comparisons of characteristic and diffuser stability decisive flow variables are made in a chord-wise direction along the diffuser passage for full span, near shroud and near hub wall. In an operating point near the stability limit, the stabilizing effect of the hub-side wall contouring on the diffuser flow is clearly shown. In a scale-model test rig, experimental data including shroud-side transient wall pressures, pneumatic 5-hole probe data for a full diffuser blade-to-blade passage, static wall pressures at various planes as well as total temperature were measured. The experimental data is utilized for validation of the presented numerical calculations. The flow stabilizing effect of the hub-wall contouring was clearly visible in the measurements, which showed 8% range extension at highest circumferential Mach number Mu~2~=1.16.


Experimental and Numerical Study of an Open Impeller Centrifugal Compressor Stage Utilising 3D Diffuser End Wall Contouring for Operating Range Extension

Division / Sponsor:
International Gas Turbine Institute (IGTI)

Paper Proceedings: https://asmedigitalcollection.asme.org/GT/GT2020/volume/84058

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