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  • 1
    Electronic Resource
    Electronic Resource
    Transition from spiral- to bubble-type vortex breakdown (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 8 (1996), S. 1330-1332 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Numerical calculations employing the fully three-dimensional, time-dependent Navier–Stokes equations have been utilized to compute a transition from spiral- to bubble-type vortex breakdown for an unconfined longitudinal vortex. The transition was initiated through a small increase in the magnitude of the free-stream axial velocity deceleration. The resulting bubble structure, which consisted of a single toroidal recirculation cell, ultimately grew unstable. Transition back to a stronger spiral breakdown followed. Results are in qualitative agreement with experimental observations. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.868902
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  • 2
    Electronic Resource
    Electronic Resource
    Numerical simulation of bubble-type vortex breakdown within a tube-and-vane apparatus (2000)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 12 (2000), S. 603-608 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Numerical calculations for three-dimensional, unsteady, laminar, bubble-type vortex breakdown within a tube-and-vane-type apparatus at a Reynolds number of 2000 and circulation number Ω=1.41 are presented. This study is unique in that rather than specifying the inlet swirl velocity through a fit to experimental data (or a Burgers profile), the swirl was induced by directing the fluid through an array of 16 turning vanes, the arrangement being similar to that employed in the original experimental works of Sarpkaya [J. Fluid Mech. 45, 545 (1971); AIAA J. 12, 602 (1974)]. The interior of the resulting breakdown bubble consisted of one primary torroidal recirculation cell, which was tilted from, and found to gyrate about, the bubble centerline. The dominant frequency of gyration was identified, and the mechanism of fluid exchange examined. Subsequent calculations were performed using fixed inlet swirl and axial velocity profiles that were obtained from the results computed using the full geometry (including the turning vanes). Results revealed no significant difference in the downstream breakdown location or structure. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.870266
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  • 3
    Electronic Resource
    Electronic Resource
    Linear stability of swirling flows computed as solutions to the quasi-cylindrical equations of motion (1993)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 17 (1993), S. 291-300 
    Details
    ISSN: 0271-2091
    Keywords: Vortex breakdown ; Linear stability ; Swirling flows ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: The linear stability of numerical solutions to the quasi-cylindrical equations of motion for swirling flows is investigated. Initial conditions are derived from Batchelor's similarity solution for a trailing line vortex. The stability calculations are performed using a second-order-accurate finite-difference scheme on a staggered grid, with the accuracy of the computed eigenvalues enhanced through Richardson extrapolation. The streamwise development of both viscous and inviscid instability modes is presented. The possible relationship to vortex breakdown is discussed.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/fld.1650170403
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  • 4
    Electronic Resource
    Electronic Resource
    Numerical calculations of three-dimensional turbulent vortex breakdown (1995)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 20 (1995), S. 307-318 
    Details
    ISSN: 0271-2091
    Keywords: vortex breakdown ; turbulence ; computational fluid dynamics ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Numerical solutions to the three-dimensional, unsteady, incompressible Reynolds-averaged Navier-Stokes equations have been obtained for bubble-type vortex breakdown. Two different turbulence models were employed: (1) standard K-ε and (2) an explicit, regularized algebraic Reynolds stress model. Results are computed at a Reynolds number of 10,000. The algebraic Reynolds stress model produced a breakdown bubble with a larger length-to-diameter ratio than did the K-ε model. Breakdown also occurred at lower levels of adverse pressure gradient for the algebraic stress model than for the K-ε model. In each case single-cell breakdown structures resulted. This is contrasted with numerical calculations for laminar breakdown which reveal the existence of complex multicell bubble breakdown structures.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/fld.1650200404
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