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Research Papers

Influence of Unsteadiness on the Control of a Hub-Corner Separation Within a Radial Vaned Diffuser

[+] Author and Article Information
Aurélien Marsan

Département de Génie Mécanique,
Université de Sherbrooke,
Sherbrooke, QC J1K 2R1, Canada
e-mail: aurelien.marsan@usherbrooke.ca

Isabelle Trébinjac

Laboratoire de Mécanique des,
Fluides et d'Acoustique,
UMR CNRS 5509,
École Centrale de lyon,
Ecully Cedex 69134, France

Sylvain Coste, Gilles Leroy

Turbomeca,
Safran Group,
Bordes 64511, France

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received July 8, 2014; final manuscript received July 28, 2014; published online September 30, 2014. Editor: Ronald Bunker.

J. Turbomach 137(2), 021008 (Sep 30, 2014) (12 pages) Paper No: TURBO-14-1125; doi: 10.1115/1.4028244 History: Received July 08, 2014; Revised July 28, 2014

The present work aims at evaluating the effect of the impeller–diffuser interaction on the control of a hub corner separation, which develops in the radial vaned diffuser of a centrifugal compressor designed and built by Turbomeca, Safran group. Unsteady numerical simulations of the flow in the aspirated centrifugal compressor are then performed. Numerical results are validated by comparison with the available experimental results. The analysis of the numerical flow field shows that the hub-corner separation is not completely removed by the suction, on the contrary to the steady-state results that were obtained in previous work. The boundary layer separation is only translated downstream. Its location is explained by the scrolling of the pressure waves generated by the impeller–diffuser interaction, which strengthen when crossing the diffuser throat. This result highlights the major role played by the impeller–diffuser interaction, which should be taken into account for developing control strategies in radial vaned diffusers, and stresses the shortcoming of the steady-state numerical model when suction is applied.

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References

Figures

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Fig. 1

Total-to-static pressure ratio. Steady-state numerical results. Without (circles) and with (triangles) suction [8].

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Fig. 2

Performance of the diffuser—experimental/numerical—no suction

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Fig. 3

Unsteady pressure signals in the diffuser—shroud wall. Numerical versus experimental [9].

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Fig. 4

View of the low-momentum flow zone. Isosurface at Mach number = 0.1 [10].

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Fig. 5

Topology of the separation. URANS—time-averaged [10].

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Fig. 6

Location of the suction slot

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Fig. 7

Diffuser static pressure recovery coefficient: without/with suction

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Fig. 8

Diffuser total pressure losses coefficient: without/with suction

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Fig. 9

Steady-state skin-friction patterns: without and with suction

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Fig. 10

Three-dimensional streamlines—RANS calculations—with suction (view from downstream)

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Fig. 11

Blockage in the diffuser, near hub, and shroud

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Fig. 12

Global blockage ratio: without and with suction

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Fig. 13

Static pressure recovery coefficient of the subcomponents of the diffuser

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Fig. 14

Instantaneous skin-friction pattern: with suction

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Fig. 15

Comparison between streamlines of the time-averaged flow field and trajectories

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Fig. 16

Time-averaged skin-friction patterns: without and with suction

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Fig. 17

Maxima of the steady-state (up), time-averaged (middle), and instantaneous (down) adverse pressure gradient—10% of vein height—with suction

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Fig. 18

Propagation of a high pressure waves in the diffuser

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Fig. 19

Characteristic curves of the diffuser subcomponents—URANS, without and with suction

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Fig. 20

Blockage in the diffuser—URANS, without and with suction

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Fig. 21

Three-slots suction strategy—URANS, without suction

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