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  • 1
    Digitale Medien
    Digitale Medien
    The effect of mobility gradients on viscous instabilities in miscible flows in porous media (1999)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 11 (1999), S. 740-742 
    Details
    ISSN: 1089-7666
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The onset of viscous instability and the subsequent fingering have been mostly studied under conditions of a sharp mobility contrast. In stable miscible flows in porous media, however, mobility gradients of variable extent can develop due to hydrodynamic dispersion. Graded mobility and density profiles will affect instabilities, either by mitigating (in the case of a monotonic variation) or by enhancing (nonmonotonic variation) the rates of growth. The mitigating effect was exploited by Claridge and Gorrel and Homsy for the optimal design of graded mobility banks. Hickernell and Yortsos showed that in the linear stability limit, the growth rate is controlled by the maximum of the logarithmic derivative of the mobility profile. We present an experimental study of miscible displacements in porous media to study effects of mobility gradients in viscous instability. We take advantage of molecular diffusion in miscible displacements to create a mobility gradient zone and subsequently initiate the instability by increasing the displacement velocity. A theoretical analysis based on linear stability is used to analyze the experimental results. © 1999 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.869943
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  • 2
    Digitale Medien
    Digitale Medien
    The effect of dispersion on the stability of non-monotonic mobility profiles in porous media (1998)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 10 (1998), S. 747-749 
    Details
    ISSN: 1089-7666
    Quelle: AIP Digital Archive
    Thema: Physik
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.869579
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  • 3
    Digitale Medien
    Digitale Medien
    Hydrodynamic dispersion broadening of a sedimentation front (1994)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 6 (1994), S. 3215-3217 
    Details
    ISSN: 1089-7666
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Hydrodynamic dispersion is responsible for the spreading of the sedimentation front even in a noncolloidal monodisperse suspension. Measurements of the broadening of the top front observed during sedimentation have been used in determining the hydrodynamic dispersion coefficient. Hindered settling has an opposed effect and leads to the self-sharpening of the front. Both effects have to be taken into account simultaneously. This Letter provides a simple, but complete determination of the space and time concentration profile and shows that the final front should consist of a steady-shape profile propagating at constant velocity. With such a solution, the data of Davis et al. [AIChE J. 34, 123 (1988); J. Fluid Mech. 196, 107 (1988)] give hydrodynamic dispersion coefficient five times larger than their former analysis, in agreement with Lee et al. [Phys. Fluids A 4, 2601 (1992)].
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.868051
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  • 4
    Digitale Medien
    Digitale Medien
    Dispersion, permeability heterogeneity, and viscous fingering: Acoustic experimental observations and particle-tracking simulations (1993)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 5 (1993), S. 1558-1574 
    Details
    ISSN: 1089-7666
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Stable and unstable displacement experiments were performed in millstone and limestone cores. Concentration histories at ten locations along the core samples were obtained by acoustic measurements. Particle-tracking simulations of the displacements were also made utilizing permeability distributions measured with a permeameter. The combination of experimental observations and simulations indicate that superstable (M〈1) displacements suppress the influence of heterogeneity; this suppression was reflected in smaller apparent dispersivities as the mobility ratio decreased below unity. In the millstone, which exhibited random heterogeneity, two-dimensional particle-tracking simulations reproduce with reasonable accuracy the growth of the fingered region in unstable displacements. In homogeneous porous media, concentration histories obtained in three-dimensional simulations did not differ significantly from their two-dimensional counterparts. In the more heterogeneous limestone, unstable displacements accentuated the influence of heterogeneity leading to longer transition zones. Two distinct flow regimes were observed in unstable displacements: (1) an initial period of rapid transition zone growth and (2) a subsequent period in which leading and trailing edges of the transition zone travel at nearly constant velocities.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.858833
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  • 5
    Digitale Medien
    Digitale Medien
    Anomalous dispersion and finite-size effects in hydrodynamic dispersion (1990)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 2 (1990), S. 674-680 
    Details
    ISSN: 1089-7666
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Anomalous dispersion refers to concentration profiles that exhibit long-time tails as opposed to normal or Gaussian dispersion, which does not exhibit such tails. An original acoustic technique has enabled experimentally the demonstration that, in an unsaturated porous medium, the observed non-Gaussian dispersion is due only to finite-size effects: the sample length is set too small to achieve a statistical Gaussian random walk. An accurate fit to the data with a semiphenomenological model is suitable for comparison with a nonlocal theory concerning this transient effect. Thus the mechanism involved in the dispersion process, and also, the characteristic length of this dispersion, can be determined.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.857720
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  • 6
    Digitale Medien
    Digitale Medien
    Simulations of viscous flows of complex fluids with a Bhatnagar, Gross, and Krook lattice gas (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 8 (1996), S. 3200-3202 
    Details
    ISSN: 1089-7666
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We address the question of using a lattice gas method to study flows of complex fluids, such as non-Newtonian or miscible fluids. A Bhatnagar, Gross, and Krook lattice technique provides a tool to simulate the flow of one fluid and the diffusion of a tracer in that fluid. We extend the technique to flows in which the viscosity is space and time dependent. This approach is suitable for non-Newtonian fluids (shear dependent viscosity) and miscible fluids (concentration dependent viscosity). The modified scheme is tested on physical flow situations, analytically tractable for the sake of comparison. © 1996 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.869093
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  • 7
    Digitale Medien
    Digitale Medien
    Accurate determination of the sedimentation flux of concentrated suspensions (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 7 (1995), S. 2510-2512 
    Details
    ISSN: 1089-7666
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Flow rate jumps are used to generate propagating concentration variations in a counterflow stabilized suspension (a liquid fluidized bed). An acoustic technique is used to measure accurately the resulting concentration profiles through the bed. Depending on the experimental conditions, we have observed self-sharpening, or/and self-spreading concentration fronts. Our data are analyzed in the framework of Kynch's theory, providing an accurate determination of the sedimentation flux [CU(C); U(C) is the hindered sedimentation velocity of the suspension] and its derivatives in the concentration range 30%–60%. In the vicinity of the packing concentration, controlling the flow rate has allowed us to increase the maximum packing up to 60%. © 1995 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.868696
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  • 8
    Digitale Medien
    Digitale Medien
    A study of the sedimentation of noncolloidal bidisperse, concentrated suspensions by an acoustic technique (1994)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 6 (1994), S. 3809-3817 
    Details
    ISSN: 1089-7666
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: This paper uses an acoustic technique to determine the concentration profile developing during the sedimentation of noncolloidal bidisperse suspensions of glass beads in a Newtonian fluid. Various bead diameter ratios have been used and a wide range of relative concentrations is covered. From the shock front velocities and the concentrations in different zones, the sedimentation velocities of small and large particles in a homogeneous suspension of respective concentrations cs0 and cl0 have been determined. The semidilute regime (c0=ss0+cl0〈20%) has many similarities with the dilute regime, where large particles provide the dominant hydrodynamic hindrance to settling. In the concentrated regime (c0(approximately-greater-than)35%), a mutual hindrance leads to a velocity reduction of large particles and to an enhancement of small ones, as compared to a monodisperse suspension. The data clearly demonstrate that size segregation in the concentrated regime disappears at a critical concentration, which for the size ratio 1.68 is equal to c0=45%. © 1994 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.868372
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  • 9
    Digitale Medien
    Digitale Medien
    Gravitational instability of miscible fluids in a Hele-Shaw cell (2002)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 14 (2002), S. 902-905 
    Details
    ISSN: 1089-7666
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We revisit the Rayleigh–Taylor instability when the two fluids are miscible and in the geometry of a Hele-Shaw cell. We provide analytical dispersion relations for the particular cases of either a sharp front between the two fluids or of a uniform density gradient stratification and for various fluid flow models, including an unbounded geometry, a two-dimensional gap-averaged Navier–Stokes–Darcy equation, and an effective porous medium. The results are compared to three-dimensional lattice BGK simulations, based on which the relevance of the various models in different wavelength regimes is discussed. © 2002 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1431245
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  • 10
    Digitale Medien
    Digitale Medien
    The threshold of the instability in miscible displacements in a Hele–Shaw cell at high rates (2001)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 13 (2001), S. 799-801 
    Details
    ISSN: 1089-7666
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: For sufficiently large viscosity ratios and injection rates, miscible displacements in a vertical Hele–Shaw cell at high rates become unstable, leading to three-dimensional (3D) fingering patterns. Below the instability threshold, the base state is 2D in the form of a "tongue" of constant thickness. We apply the long wave Saffman–Taylor stability analysis to find an expression for the threshold of instability as a function of the viscosity ratio and the injection rate. The results are in agreement with the experimental data. © 2001 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1347959
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