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Research Papers

A Three-Dimensional Time-Accurate Computational Fluid Dynamics Simulation of the Flow Field Inside a Vaneless Diffuser During Rotating Stall Conditions

[+] Author and Article Information
Michele Marconcini

Department of Industrial Engineering,
University of Florence,
Via di Santa Marta, 3,
Firenze 50139, Italy
e-mail: michele.marconcini@unifi.it

Alessandro Bianchini, Matteo Checcucci, Giovanni Ferrara, Andrea Arnone

Department of Industrial Engineering,
University of Florence,
Via di Santa Marta, 3,
Firenze 50139, Italy

Lorenzo Ferrari

National Research Council (CNR-ICCOM),
Department of Industrial Engineering,
Via di Santa Marta, 3,
Firenze 50139, Italy
e-mail: lorenzo.ferrari@iccom.cnr.it

Davide Biliotti

GE Oil & Gas,
Via Felice Matteucci 10,
Firenze 50127, Italy
e-mail: davide.biliotti@ge.com

Dante Tommaso Rubino

GE Oil & Gas,
Via Felice Matteucci 10,
Firenze 50127, Italy

1Corresponding author.

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received July 18, 2016; final manuscript received August 31, 2016; published online September 27, 2016. Editor: Kenneth Hall.

J. Turbomach 139(2), 021001 (Sep 27, 2016) (9 pages) Paper No: TURBO-16-1160; doi: 10.1115/1.4034633 History: Received July 18, 2016; Revised August 31, 2016

An accurate characterization of rotating stall in terms of inception modality, flow structures, and stabilizing force is one of the key goals for high-pressure centrifugal compressors. The unbalanced pressure field that is generated within the diffuser can be in fact connected to a non-negligible aerodynamic force and then to the onset of detrimental subsynchronous vibrations, which can prevent the machine from operating beyond this limit. An inner comprehension on how the induced flow pattern in these conditions affects the performance of the impeller and its mechanical stability can therefore lead to the development of a more effective regulation system able to mitigate the effects of the phenomenon and extend the left-side margin of the operating curve. In the present study, a 3D-unsteady computational fluid dynamics (CFD) approach was applied to the simulation of a radial stage model including the impeller, the vaneless diffuser, and the return channel. Simulations were carried out with the TRAF code of the University of Florence. The tested rotor was an industrial impeller operating at high peripheral Mach number, for which unique experimental pressure measurements, including the spatial reconstruction of the pressure field at the diffuser inlet, were available. The comparison between experiments and simulations showed a good matching and corroborated the CFD capabilities in correctly describing also some of the complex unsteady phenomena taking place in proximity of the left margin of the operating curve.

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References

Figures

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Fig. 1

Schematic view of the tested configuration

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Fig. 2

Dynamic pressure probes distribution [23]

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Fig. 3

Three-dimensional view of the computational mesh: (a) impeller and vaneless diffuser and (b) return channel

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Fig. 4

(a) Normalized work coefficient τ/τstall and (b) normalized head coefficient τηp/(τηp)stall as a function of the normalized flow coefficient ϕ/ϕstall

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Fig. 5

Unsteady simulations: evolution of the nondimensional lift over the impeller blade surface during 84 time periods

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Fig. 6

Unsteady simulations: normalized work coefficient and flow coefficient evolution during 84 time periods

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Fig. 7

Instantaneous absolute Mach number contours at midspan during rotating stall (a) t/T=20, (b) t/T=61, (c) t/T=66, (d) t/T=71, (e) t/T=76, and (f) t/T=81

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Fig. 8

Comparison between (a) measured and (b) computed differential pressure evolution in half diffuser at Sect. 20 during 20 full revolutions

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Fig. 9

Instantaneous differential pressure distribution at impeller trailing edge (Sect. 2), diffuser inlet (Sect. 20), and diffuser outlet (Sect. 40)

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Fig. 10

Instantaneous differential pressure distribution at diffuser inlet (Sect. 20) as a function of circumferential and spanwise directions

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Fig. 11

Dark curve—power spectrum at Sect. 20 and θ=0 obtained during periods from t/T=61 to t/T=81. Light curve—experimental power spectrum at Sect. 20 during the time period reported in Fig. 8(a).

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Fig. 12

Differential pressure evolution at Sect. 20 for three azimuthal locations θ=0,  π/2,  π between periods 71 and 81

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Fig. 13

Time-space map of differential static pressure evolution

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Fig. 14

Differential pressure evolution at Sect. 20 and θ=0 between periods 73 and 75

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Fig. 15

Differential pressure evolution at Sect. 20 and θ=0 between periods 61 and 71

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Fig. 16

Instantaneous entropy rise contours superimposed to radial velocity isolines (negative values) during one impeller revolution (a) t/T=61, (b) t/T=61+1/2, and (c) t/T=62

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