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  • 1
    Digitale Medien
    Digitale Medien
    The influence of interface profile on the onset of long-wavelength Marangoni convection (1998)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 10 (1998), S. 3230-3232 
    Details
    ISSN: 1089-7666
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Recent experimental results [J. Fluid Mech. 345, 45 (1997)] for long-wavelength surface-tension-driven rupture of thin liquid layers (∼0.01 cm) found the onset for significantly smaller imposed temperature gradients than predicted by linear stability analyses that assume an initially flat interface with periodic boundary conditions. The presence of sidewalls and other aspects of the experiment, however, led to deformed interfaces even with no imposed temperature gradient. These sidewall effects were not due to a small system size since experiments with aspect ratios as large as 450 were significantly affected. The stability analysis presented here takes into account the effects of the deformed interface profile and shows that these effects account for some of the disagreement between experiment and theory. In addition, deviations from standard linear stability theory caused by these effects have the same qualitative behavior as the deviations seen in the experiments. © 1998 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.869857
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  • 2
    Digitale Medien
    Digitale Medien
    Observation of helical traveling-wave convection in a liquid bridge (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 9 (1997), S. 1850-1852 
    Details
    ISSN: 1089-7666
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We use infrared imaging to visualize time-dependent flow in a liquid bridge (Prandtl number 35 and aspect ratio 1) with an imposed vertical temperature gradient. The primary instability leads from an axisymmetric time-independent state to helical traveling waves with an azimuthal wavenumber m=1. A secondary instability introduces an additional traveling wave with m=2. The structure and phase of the modes is determined from the infrared images. © 1997 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.869304
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  • 3
    Digitale Medien
    Digitale Medien
    The observability of hexagons in modulated Rayleigh–Bénard convection (1987)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 30 (1987), S. 603-604 
    Details
    ISSN: 1089-7666
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The prediction of Roppo, Davis, and Rosenblat [Phys. Fluids 27, 796 (1984)] that hexagons should appear near threshold in a Rayleigh–Bénard cell under external modulation of the temperature is reconsidered with a view to determining the experimental observability of the effect. It is found that in the limit of low-modulation amplitude δ considered by Roppo et al. the effects are qualitatively as given by these authors, but considerably smaller quantitatively. The validity limits of the small-δ expansion are clarified and results of an alternative theory of hexagonal effects, valid at arbitrary amplitude δ and frequency ω, are briefly summarized. Hexagons will only be observable if large amplitudes can be achieved.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.866359
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  • 4
    Digitale Medien
    Digitale Medien
    Traveling wave instability in sustained double-diffusive convection (1994)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 6 (1994), S. 3923-3935 
    Details
    ISSN: 1089-7666
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Experiments on buoyancy-driven double-diffusive convection sustained by imposed vertical concentration gradients (one stabilizing, the other destabilizing) have been conducted in a thin (Hele–Shaw) isothermal rectangular cell. Novel gel-filled membranes were used to sustain the concentrations at the boundaries. When the destabilizing solute diffuses more rapidly than the stabilizing one, the primary instability leads to traveling waves with a high reflection coefficient at the ends of the cell. The measured critical Rayleigh numbers and frequencies are in reasonable accord with a stability analysis that includes corrections for the finite thickness of the cell and cross-diffusion effects. The weakly nonlinear waves that appear at onset do not stabilize, even very close to the transition, but continue to evolve, eventually becoming a packet of large amplitude plumes. The packet travels back and forth along the cell in a nearly periodic manner. This behavior and the absence of measurable hysteresis are consistent with the present weakly nonlinear analysis which predicts tricritical scaling (∼ε1/4 rather than the usual ε1/2) all along the instability boundary. However, the range of this scaling in ε was found to be less than 0.005, which is inaccessible in the present experiments. © 1994 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.868383
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  • 5
    Digitale Medien
    Digitale Medien
    Convection and Diffusion in Patterns in Oscillated Granular Media (1998)
    Springer
    Journal of statistical physics 93 (1998), S. 449-465 
    Details
    ISSN: 1572-9613
    Schlagwort(e): Granular media ; pattern ; convection ; enhanced diffusion ; granular temperature ; numerical simulation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract Motions of individual particles within the stripe and square patterns formed in oscillated granular media are studied using numerical simulations. Our event-driven molecular dynamics simulations yield standing wave patterns in good accord with those observed in experiments at the same frequency and acceleration amplitude. The patterns are subharmonic and so return to their initial macroscopic state after two external cycles. However, simulations reveal that individual particles do not return to their initial position. In addition to diffusive motion, an organized flow of particles within the patterns is found; associated with each peak and each valley of the pattern is a pair of counterrotating convection rolls. The diffusion is anisotropic: transport perpendicular to stripes is enhanced over that parallel to stripes. This enhancement is computed as a function of the layer depth, acceleration amplitude, frequency, and coefficient of restitution of the particles, and is attributed to the effect of the advective motion. Velocity distributions, granular temperature, and the dependence of the diffusion coefficient parallel to the stripes on the average granular temperature are studied.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/B:JOSS.0000033158.05927.3f
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