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  • 1
    Electronic Resource
    Electronic Resource
    Funnel-shaped vortical structures in wall turbulence (1994)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 6 (1994), S. 3035-3050 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The structure of the turbulent boundary layer in a horizontal open channel was investigated experimentally by means of laser Doppler anemometry (LDA) and by flow visualization synchronized with the LDA. These experiments indicate that the dominant structures in the wall region are large scale streamwise vortices which originate at the wall and grow and expand into the outer flow region. The shape of the vortices is that of an expanding spiral, wound around a funnel which is laid sideways in the direction of flow. Most of the observations of wall turbulence phenomena made over the years, such as quasistreamwise vortices, ejections, and sweeps seem to be part of these funnel-shaped vortices.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.868129
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Low-speed streaks in drag-reduced turbulent flow (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 9 (1997), S. 2397-2404 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effect of a surfactant drag-reducing additive (530 ppm Habon G solution) on the structure of wall turbulence, both in a flume and in pipe flow, was investigated experimentally. Real-time infrared thermography was used for flow visualization and measurements of the spanwise spacing between the thermal streaks. The experiments were carried out over a broad range of friction velocities, i.e., up*=0.51–3.27 cm/s. With wall shear velocities1.54≤up*≤3.27 cm/s drag reduction of 82%–85% was achieved in a tube flow, well below the predictions of the Virk maximum drag reduction asymptote proposed for high polymers. The results of spanwise streak spacing indicate that wall shear velocity may be an appropriate parameter for describing nondimensional streak spacing behavior in drag reducing flows. A hypothesis, based on the average spanwise streak spacing λ+, can be applied to describe the mean velocity profiles of Habon G solutions. The ratio (λp+−100)/100 was applied to describe mean velocity profiles with 530 ppm Habon G solution. ©1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.869469
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Particle behavior in the turbulent boundary layer. II. Velocity and distribution profiles (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 7 (1995), S. 1107-1121 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The velocity, flux, and concentration distribution of solid particles in a turbulent boundary layer of a horizontal water flume were investigated experimentally by means of LDA and visualization techniques. The particles were of polystyrene (specific density ∼1.05). Results show that coherent wall structures are responsible for most of the characteristics of particle behavior throughout the boundary layer. Particles are often concentrated in regions of low velocity, associated with wall structures, and as a result the average particle velocity is lower than the fluid's. This was also noted previously by Rashidi et al., but not explained. The actual relative velocity between the particles and the surrounding fluid is often small. In addition, the data suggest that as the shear rate increases, the particle flux profiles asymptotically approach a shape where a strong gradient of particle flux exists in the lower part of the boundary layer (y+≤250), while it is relatively constant at higher elevations. This phenomenon may also be attributable to interactions with the wall structures. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.868552
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  • 4
    Electronic Resource
    Electronic Resource
    Wave–turbulence interaction in free-surface channel flows (1992)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 4 (1992), S. 2727-2738 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Wave–turbulence interaction in turbulent channel flows has been studied using microbubble tracers and visualization. In the experiments, two-dimensional waves of different lengths and amplitudes have been superimposed on a turbulent channel flow via a wavemaker. The conditions were chosen to be such that the frequencies of the interfacial waves were in the range of the ejection frequencies in the undisturbed flow. The results show that the waves cause an increase in the number of wall ejections, giving rise to an increase in the measured values of the turbulence intensities and Reynolds stresses. However, the increases in ejection frequency do not appear to be directly related to wave frequency. They correlate better with wave amplitude. Conditional averaging of the velocity fields shows that while turbulence is increased in the region below the crest of the waves (extending to the wall), it is decreased in the wave troughs. The overall effect of the surface waves, over the range of conditions investigated is, however, to increase turbulence levels.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.858331
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  • 5
    Electronic Resource
    Electronic Resource
    Particle behavior in the turbulent boundary layer. I. Motion, deposition, and entrainment (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 7 (1995), S. 1095-1106 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The motion of solid particles near the wall in a turbulent boundary layer was investigated experimentally in a water flume by flow visualization techniques and by LDA. The particles were of polystyrene (specific density ∼1.05) with diameters ranging from 100 to 900 μm. Results show that particle motion, as well as entrainment and deposition processes, are controlled by the action of coherent wall structures, which appear to be funnel vortices. The behavior of the particles is consistent with the motion and effects of such vortices. The vortices appear to cause the formation of particle streaks near the wall, to create suitable conditions for particle entrainment, and to assist in particle deposition by conveying them from the outer flow to the wall region. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.868551
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    Paper (German National Licenses)
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  • 6
    Electronic Resource
    Electronic Resource
    Erratum: "Funnel-shaped vortical structures in wall turbulence'' [Phys. Fluids 6, 3035 (1994)] (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 7 (1995), S. 452-452 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.868786
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    Paper (German National Licenses)
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  • 7
    Electronic Resource
    Electronic Resource
    The flow in and around a droplet or bubble submerged in an unbound arbitrary velocity field (1970)
    Springer
    Rheologica acta 9 (1970), S. 488-496 
    Details
    ISSN: 1435-1528
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Zusammenfassung Das Problem der Strömungsfelder in einer unbegrenzten Flüssigkeit wird sowohl innerhalb wie außerhalb eines einzelnen kugelförmigen Tropfens für den allgemeinen Fall gelöst, wenn die ungestörte Geschwindigkeit durch dieStokessche Gleichung angegeben werden kann, aber sonst willkürlich ist. Es wird eine allgemeine Formel für die Geschwindigkeit, die nach langer Zeit erreicht wird, angegeben. Sie enthält als Spezialfall die Lösungen vonHadamard-Rybczynski, Taylor u. a. Die schleppende Kraft, die auf den Tropfen einwirkt, wird formuliert. Diese Formel enthält das Gesetz vonFaxen als Spezialfall. Die Funktion der Grenzfläche und ihre Abweichung von der Kugelform wird bestimmt. Sie kann zur Bestimmung genauerer Strömungsfelder in einem Iterationsverfahren angewendet werden.
    Notes: Summary A solution is presented for the flow fields interior and exterior to a single spherical droplet submerged in an unbounded fluid, for the general case when the unperturbed velocity isStokesian but otherwise quite arbitrary. A general equation for the terminal settling velocity is derived which contains as special cases the solutions ofHadamard-Rybczynski, Taylor and others. The drag force on a spherical droplet is also formulated. This equation contains as a special case the law ofFaxen. The function describing the interface and its deviation from sphericity is derived. This may be used for determining more accurate flow fields in an iterative procedure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01985457
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    Paper (German National Licenses)
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  • 8
    Electronic Resource
    Electronic Resource
    Hydrodynamics of a drop submerged in an unbounded arbitrary velocity field in the presence of surfactants (1972)
    Springer
    Flow, turbulence and combustion 25 (1972), S. 215-233 
    Details
    ISSN: 1573-1987
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract A solution is presented for the flow fields interior and exterior to a single spherical droplet submerged in an unbounded fluid, for the general case when the unperturbed velocity is Stokesian but otherwise arbitrary. Surface-active-agents are present in the system and are included in the analysis. A general equation for the terminal settling velocity is derived which contains as special cases the familiar solutions of Levich and our previous solution. Also derived is a general expression for the drag force. This expression contains as special cases the Laws of Faxen and our previous results. The function describing the interface and its deviation from sphericity is derived. This may be used for determining more accurate flow fields in an iterative procedure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00382297
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    Paper (German National Licenses)
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