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  • 1
    Digitale Medien
    Digitale Medien
    The axisymmetric boundary layer beneath a Rankine-like vortex (1997)
    Springer
    Experiments in fluids 22 (1997), S. 300-311 
    Details
    ISSN: 1432-1114
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract  An experimental investigation of the three-dimensional boundary layer induced by a Rankine-like vortex with its axis normal to a stationary disk is described. The velocity field through the boundary layer was measured for Reynolds number Re (based on the tangential velocity and radius at the disk edge) ranging from 10 000 to 25 000 at various radial distances by means of a 4-beam, 2-component Laser Doppler Anemometer. Our results show that the nature of the boundary layer is affected by two factors: an inflexional instability caused by the crossflow velocity profile and a stability factor caused by the favorable pressure gradient. At lower Reynolds number, the radial pressure gradient has a very strong stabilizing effect on the boundary layer and acts to revert it to its laminar state upstream of the effusing core. At higher Re the inflexional instability caused by the crossflow velocity dominates while the stabilizing influence of the favorable pressure gradient recedes. As such, laminar reversion likely occurs closer to the effusion core. Thus, the point of laminar reversion moves closer to the effusion core as the Reynolds number is increased.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s003480050052
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  • 2
    Digitale Medien
    Digitale Medien
    Strong interaction between a buoyancy bubble and a free surface (1996)
    Springer
    Theoretical and computational fluid dynamics 8 (1996), S. 73-88 
    Details
    ISSN: 1432-2250
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Physik
    Notizen: Abstract The growth and collapse of buoyant vapor bubbles close to a free surface in an inviscid incompressible fluid is investigated in this paper. The strong interaction between the deforming bubble and the free surface is simulated numerically by a boundary-integral method (Taib 1985; Blake et al., 1987). Improvements are made in the calculation of the singular integrals, the use of nonuniform boundary elements, and the choice of time-step size. The present numerical results agree better with the experimental observations of Blake and Gibson (1981) than previous numerical predictions for bubbles initiated at one maximum radius from the free surface. There is also concurrence of flow features with the experiments for a bubble initiated as close as half maximum radius from the free surface, where other numerical efforts have failed. The effects of buoyancy on bubbles initiated close to a free surface are also investigated. Vastly different features, depending on the distance of the bubble to the free surface and the buoyancy-force parameter, have been observed.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00312403
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  • 3
    Digitale Medien
    Digitale Medien
    The absolute instability of boundary-layer flow over viscoelastic walls (1996)
    Springer
    Theoretical and computational fluid dynamics 8 (1996), S. 237-252 
    Details
    ISSN: 1432-2250
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Physik
    Notizen: Abstract The linear stability of boundary-layer flow over a viscoelastic-layer wall is considered. A companion matrix technique is used to formulate the stability problem as a linear matrix eigenvalue problem for complex frequency and all the eigenvalues may be determined without any initial guess values. The eigenvalues are compared with those obtained with an accurate shooting method. The instability character of the boundary-layer flow is further investigated with the purpose of finding the conditions under which the instability of the flow could become absolute. The mapping technique of Kupferet al. (1987) is used to identify the occurrence of absolute instability eigenvalues. Absolute instabilities are discovered for cases of soft damped wall over certain ranges of Reynolds number. The effects of wall material stiffness, damping coefficient, thickness of layer, and Reynolds number on the occurrence of absolute instability are examined and presented.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00639694
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  • 4
    Digitale Medien
    Digitale Medien
    The Absolute Instability of Boundary-Layer Flow over Viscoelastic Walls (1996)
    Springer
    Theoretical and computational fluid dynamics 8 (1996), S. 237-252 
    Details
    ISSN: 1432-2250
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Physik
    Notizen: Abstract  The linear stability of boundary-layer flow over a viscoelastic-layer wall is considered. A companion matrix technique is used to formulate the stability problem as a linear matrix eigenvalue problem for complex frequency and all the eigenvalues may be determined without any initial guess values. The eigenvalues are compared with those obtained with an accurate shooting method. The instability character of the boundary-layer flow is further investigated with the purpose of finding the conditions under which the instability of the flow could become absolute. The mapping technique of Kupfer et al. (1987) is used to identify the occurrence of absolute instability eigenvalues. Absolute instabilities are discovered for cases of soft damped wall over certain ranges of Reynolds number. The effects of wall material stiffness, damping coefficient, thickness of layer, and Reynolds number on the occurrence of absolute instability are examined and presented.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00639694
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  • 5
    Digitale Medien
    Digitale Medien
    A numerical study of the effect of free surface and water depth on the stability of wakes: use of GDQ formulation (1997)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 24 (1997), S. 1079-1090 
    Details
    ISSN: 0271-2091
    Schlagwort(e): wake flow ; free surface ; instability ; GDQ method ; Engineering ; Numerical Methods and Modeling
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Maschinenbau
    Notizen: The instability character of a wake in the presence of a free surface is examined by a recently developed GDQ (generalized differential quadrature) numerical method. It is shown that at low Froude number the wake near a free surface is convectively unstable, but when the Froude number is increased further it becomes absolutely unstable. The effect of water depth on the stability property of the wake flow is also investigated. It is found that the influence of water depth on the critical point of instability is limited to at most 20% variation in the complex frequency, while the change in temporal growth rate is also limited to about 20%. © 1997 John Wiley & Sons, Ltd.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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