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  • 1
    Electronic Resource
    Electronic Resource
    Influence of precession on velocity measurements in a strong laboratory vortex (1999)
    Springer
    Experiments in fluids 27 (1999), S. 181-188 
    Details
    ISSN: 1432-1114
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract A strong laboratory vortex is generated in a cylindrical cell using a rotating disk and stretched by pumping the fluid out through a hole in the centre of the top of the cell. The velocity field is measured by means of laser Doppler anemometry and Doppler ultrasonic anemometry which are both non intrusive methods. The vortex exhibits a slight precession which induces temporal fluctuations of the velocity at the measurement point. Due to the centrifugal force, the tracers concentrate in a tubular region around the vortex, leading to spatial variations of the measurement counting rate. Under these two effects, the probability density function (PDF) of the one point velocity exhibits a strong non-Gaussian behaviour. In order to access the details of the velocity profile of the vortex in its own system of reference, the influence of the vortex precession, of the spatial variations of the concentration in tracers and of the intrinsic measurement dispersion is investigated and a model is proposed. It allows to recover statistically the characteristics of the vortex and to deduce the trajectory of its centre from the instantaneous velocity profiles.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003480050343
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Vortex stretching in a laminar boundary layer flow (1997)
    Springer
    Experiments in fluids 22 (1997), S. 351-353 
    Details
    ISSN: 1432-1114
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract  A new technique to produce controlled stretched vortices is presented. The initial vorticity comes from a laminar boundary layer flow and the stretching is parallel to the initial vorticity. This low velocity flow enables direct observations of the formation and destabilization of vortices. Visualizations are combined with quasi-instantaneous measurements of a full velocity profile obtained with an ultra-sonic pulsed Doppler velocimeter. Several modes of destabilization are observed and include pairing of two vortices, hairpin deformation, and vortex breakdown into a coil shape.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003480050059
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Vortex dynamics investigation using an acoustic technique (1999)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 11 (1999), S. 3380-3389 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A new acoustic technique using the double time-reversal mirrors system and based on geometrical acoustics, is used to study a vortical flow. The interaction between the sound and a vortex is described in details. This technique has been applied to the study of a stretched vortex. This vortex is generated by stretching the vorticity of a boundary layer in a low velocity water channel. It is shown that the velocity field can be reconstructed from the phase distortion of an ultrasonic wave. The technique gives access to a complete characterization of the vortex dynamics, such as the temporal evolution of its size, its circulation and its position. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.870197
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    Wavelength selection of fingering instability inside Hele–Shaw cells (2001)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 13 (2001), S. 3120-3125 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Fingering instabilities involving fluids confined between two plates sometimes give rise to a typical wavelength λ proportional to the gap h. This unexplained behavior is investigated for the case of the Rayleigh–Taylor instability between two liquids of the same viscosity. Using qualitative scaling arguments and linear stability analysis for a simplified model of hydrodynamics, we show that, in the miscible case, h becomes a natural cut-off when diffusion is negligible, i.e., when the Péclet number Pe=h3Δρg/(ηD) is large (η viscosity, g gravitational acceleration, D diffusivity, Δρ density difference). The same result holds in the immiscible case for large capillary number Ca=h2Δρg/(12γ) (γ surface tension). In this saturation regime, the dominant wavelength is given by λ(approximate)2.3h, while in the opposite limit (low Pe or low Ca) λ scales, respectively, as h/Pe or h/Ca1/2. These results are in agreement with a recent experimental study. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1410120
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  • 5
    Electronic Resource
    Electronic Resource
    Mass and momentum transport in longitudinal vortical structures in liquid flow Example of Görtler vortices (1997)
    Springer
    Experiments in fluids 23 (1997), S. 388-394 
    Details
    ISSN: 1432-1114
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract  The difference between mass and momentum transport in longitudinal vortical structures is shown in this paper. The patterns observed by visualization using laser induced fluorescence are the signature of the mass transport, while the flow structures revealed by anemometry show the momentum transport. Experiments and numerical simulations are performed in order to compare the velocity field of the Görtler instability with the mass distribution of a passive scalar. The typical scales involved in this problem are discussed with relation to the Schmidt number, in order to compare the size of the observed “mushrooms” with the size of the longitudinal Görtler vortices. It is found that the nonlinearities which strongly influence the velocity perturbation do not modify the shape and the size of the scalar structures.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003480050126
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    Paper (German National Licenses)
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