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  • 1
    Electronic Resource
    Electronic Resource
    Spiral and circular waves in the flow between a rotating and a stationary disk (1999)
    Springer
    Experiments in fluids 26 (1999), S. 179-187 
    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  Circular and spiral waves are observed in the flow between a rotating and a stationary disk. These waves are generated by instabilities of the stationary disk boundary layer. This experimental work is devoted to their study by means of flow visualization and measurements of the associated velocity fields. In particular, instantaneous velocity profiles are measured by ultrasonic Doppler anemometry. The spatio-temporal characteristics of the waves are studied with the help of Fourier transforms of these velocity signals.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003480050278
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  • 2
    Electronic Resource
    Electronic Resource
    Appearance of a square pattern in a Rayleigh–Bénard experiment (1988)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 31 (1988), S. 3440-3442 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In this work the experimental verification of the appearance of square patterns in Rayleigh–Bénard systems is described. Convective square cells are observed above the threshold of convection in a layer of water sandwiched between two Plexiglas plates. These experimental results agree with earlier theoretical predictions [J. Fluid Mech. 139, 461 (1984); 152, 113 (1985); 178, 491 (1987)], and provide, as far as can be determined, the very first direct observation of the stability of square patterns due to a hybrid thermal boundary condition on the top and bottom of the convecting fluid layer.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.866908
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  • 3
    Electronic Resource
    Electronic Resource
    Collective behavior of wakes downstream a row of cylinders (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 8 (1996), S. 2097-2106 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: This experimental study is devoted to visualisation and ultrasonic velocity measurement of the wakes formed behind a row of parallel cylinders placed side by side, perpendicular to an incoming flow at low Reynolds numbers. When the distance separating the cylinders is small compared to their diameter, two instability mechanisms, associated with different patterns and dynamics compete. A first spatial symmetry breaking appears when the stationary wakes behind each cylinder are deviated towards one side or the other and form large clusters containing from two to sometimes more than ten wakes. These clusters are separated by intense recirculating zones. When the Reynolds number is increased, the wakes belonging to the widest clusters experience a secondary temporal oscillatory bifurcation. Classical Bénard-Von Kármán vortex streets are thus shed in phase by these cylinders (acoustic mode), by contrast with the wakes outside these cells which stay stationary. Finally, the flow around far apart cylinders is also investigated. The primary instability does not occur in this case and a perfect optical mode of vortex shedding, with neighbours in phase opposition, takes place in the flow. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.868984
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  • 4
    Electronic Resource
    Electronic Resource
    Experimental study of rotating disk instability. I. Natural flow (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 8 (1996), S. 496-508 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: This article is devoted to the study of the rotating disk flow instability. This inflectional-type instability, called a cross-flow instability, exemplary of the transition to turbulence in three-dimensional boundary layers. We first present the experimental marginal stability curve of unstable waves obtained by hot-film probe measurements and compare it with the theoretical results available in the literature. The experiment is in accordance with different theoretical determinations of the linear threshold, but we note a difference between experimental and theoretical critical wave-number values. The unstable wave dynamics is then investigated by means of experimental dispersion curves (linking frequencies to the wave-number vector components) determined by two-probe measurements. The results show, in particular, the existence of traveling dispersive waves in the boundary layer of the rotating disk. Finally, we show that the emergence of nonlinear effects occurs very early in the system, far from the transition point. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.868803
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  • 5
    Electronic Resource
    Electronic Resource
    Some new features of the passive scalar mixing in a turbulent flow (1999)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 11 (1999), S. 636-646 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We analyze experimentally the statistical properties of a turbulent mixing created in the gap between two counter-rotating disks at a Taylor Reynolds number Rλ(approximate)400. Local isotropy is investigated for the inertial and dissipative scales r, using two tests, one applied on C(r), the correlation coefficient between temperature increments and velocity increments, and the other one on S(r), the temperature increment skewness factor. When heating one of the disks and cooling the other one, either positive, negative or almost null values of C and S can be obtained at small scales as a direct result of the presence of several temperature sources. In particular, we emphasize the fact that null or small values for these quantities in the inertial range are an evidence of local isotropy of the temperature field. In these cases, we use the Vaienti et al. equation [Physica D 73, 99 (1994)] for the evolution of the temperature increments probability density functions (PDFs) to predict the inertial and dissipative range PDFs, using an initial PDF, and two measurable closure functions. The intermittent behavior quantified through these statistics is well reproduced by the numerical integration of this evolution equation. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.869935
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  • 6
    Electronic Resource
    Electronic Resource
    Experimental study of rotating disk flow instability. II. Forced flow (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 8 (1996), S. 2985-2994 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The destabilization of the rotating disk flow subject to a forcing is experimentally investigated. An isolated roughness element of size of order δ (the constant boundary layer thickness) is placed under the linear threshold of the cross-flow instability in order to create a hydrodynamic pattern of finite amplitude and localized in space. The experimental neutral stability curve is first established. The resulting double parabolic curve exhibits two minima: one of which is due to the amplification of fundamental modes, the other one is linked to the emergence of superharmonic modes. Dispersion curves determined by means of two-point measurements appear to be shifted away from those measured in the natural case (without forcing). We show that this discrepancy is due to the presence of weak nonlinear effects which can be described by a Ginzburg–Landau amplitude equation. Lastly, we present an original method that enables to determine both components of the group velocity vector using the measured dispersion relations and wave packet propagation angle. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.869076
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  • 7
    Electronic Resource
    Electronic Resource
    Stability of a traveling roll system in a rotating disk flow (1998)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 10 (1998), S. 2695-2697 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The stability of a traveling roll system, which results from the development of a primary instability of the flow between a stationary and a rotating disk, is experimentally studied. The characteristics of this traveling pattern and of the bifurcation from which it results are obtained. We show in particular that the band of the stable roll modes is limited by the Eckhaus secondary instability. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.869793
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  • 8
    Electronic Resource
    Electronic Resource
    Complex bi-orthogonal decomposition of a chain of coupled wakes
    Amsterdam : Elsevier
    Physica D: Nonlinear Phenomena 58 (1992), S. 407-413 
    Details
    ISSN: 0167-2789
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
    URL: http://linkinghub.elsevier.com/retrieve/pii/0167-2789(92)90127-9
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  • 9
    Electronic Resource
    Electronic Resource
    Statistics of temperature increments in fully developed turbulence part I. Theory
    Amsterdam : Elsevier
    Physica D: Nonlinear Phenomena 73 (1994), S. 99-112 
    Details
    ISSN: 0167-2789
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
    URL: http://linkinghub.elsevier.com/retrieve/pii/0167-2789(94)90227-5
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  • 10
    Electronic Resource
    Electronic Resource
    On the spatio-temporal structure of cylinder wakes (1999)
    Springer
    Experiments in fluids 26 (1999), S. 188-196 
    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 wake of a short aspect ratio cylinder placed in a uniform flow is experimentally investigated. After having characterized the temporal behavior of the Bénard–Von Kàrmàn vortex shedding by the use of a classical hot-wire anemometer, an ultrasound anemometry technique is applied to study the spatial critical behavior of the envelope of the transverse velocity of the wake. It is shown that this envelope which represents the spatial form of the global mode of the wake, follows universal scaling laws which are in agreement with a second order phase transition. In a second set of experiments, the behavior of the longitudinal velocity fluctuations is also investigated. It is discovered that there is a special point several diameters behind the cylinder, which plays a role of a wave maker. Finally, for very small aspect ratio cylinders, symmetric vortex shedding is reported and interpreted using a system of coupled oscillators.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003480050279
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