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Research Papers: Flows in Complex Systems

Numerical Analysis of Vortex Dynamics in a Double Expansion

[+] Author and Article Information
Allan I. J. Love

Research Engineer
e-mail: enxail@nottingham.ac.uk

Donald Giddings

Lecturer
e-mail: donald.giddings@nottingham.ac.uk

Henry Power

Professor
e-mail: henry.power@nottingham.ac.uk
Division of Energy and Sustainability,
The University of Nottingham,
Nottingham NG7 2RD, UK

Contributed by the Fluids Engineering Division of ASME for publication in the JOURNAL OF FLUIDS ENGINEERING. Manuscript received August 1, 2012; final manuscript received June 28, 2013; published online September 4, 2013. Assoc. Editor: Chunill Hah.

J. Fluids Eng 135(11), 111104 (Sep 04, 2013) (8 pages) Paper No: FE-12-1358; doi: 10.1115/1.4024955 History: Received August 01, 2012; Revised June 28, 2013

The turbulent flow through a 3D diffuser featuring a double expansion is investigated using computational fluid dynamics. Time dependent simulations are reported using the stress omega Reynolds stress model available in ANSYS FLUENT 13.0. The flow topography and characteristics over a range of Reynolds numbers from 42,000 to 170,000 is reported, and its features are consistent with those investigated for other similar geometries. A transition from a chaotic separated flow to one featuring one large recirculation in one corner of the diffuser is predicted at a Reynolds number of 80,000. For a Reynolds number of 170,000 a precessing/flapping motion of the main flow field was identified, the frequency of which is consistent with other numerical and experimental studies.

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Figures

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Fig. 1

Dimensions of the diffuser geometry

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Fig. 2

2D diffuser flow regimes. Adapted from Fox and Kline [6]. The locations of the entire diffuser and each expansion are indicated.

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Fig. 3

Flow regimes in axisymmetric sudden expansion, produced by Guo et al. [20]

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Fig. 4

A typical mesh used in the calculations

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Fig. 5

Flow variables on centerline 9D downstream of diffuser entrance (Re = 1.7×105)

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Fig. 7

Flow through the diffuser, showing the outline of the recirculation zone by isosurfaces for axial velocity of −0.01 ms-1. The centerline monitor points −1D, 1D, 3D, 5D, 7D, and 9D are shown for reference.

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Fig. 6

Resultant secondary velocities on centerline 3D downstream of the diffuser entrance

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Fig. 10

Limit cycles at different axial locations

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Fig. 9

Resultant secondary velocities on centerline downstream of the diffuser entrance

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Fig. 8

Secondary velocity vectors. The outline of the recirculation zone is shown in each case.

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Fig. 11

Frequency spectra for the resultant velocity at 5D

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