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  • 1
    Electronic Resource
    Electronic Resource
    Pressure-driven channel flows of a model liquid-crystalline polymer (1999)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 11 (1999), S. 2821-2835 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Shear flows disrupt molecular orientation in liquid-crystalline polymers (LCPs) through director tumbling, and this causes difficulty in controlling the polymer structure and properties in injection molding and extrusion. In this paper we simulate LCP channel flows using the Doi theory. A Bingham closure is used to preserve director tumbling and wagging. The objective is to examine how contractions and expansions in a channel affect LCP orientation and to explore the possibility of using the channel geometry as a means of manipulating LCP order. A finite-element method is used to solve the coupled equations for fluid flow and polymer configuration. Results show that a contraction aligns the director with the streamline and improves molecular order, while an expansion drives the director away from the flow direction and reduces molecular order. If the expansion is strong enough, an instability develops downstream as disturbances in the flow and polymer configuration reinforce each other through the polymer stress. This instability generates a wave that spans roughly the central half of the channel and propagates downstream at the centerline velocity. For abrupt contractions or expansions, disclinations of ±1/2 strength arise in the corner vortex. The numerical results agree qualitatively with experiments when comparisons can be made. In particular, the wavy pattern following a sudden expansion is remarkably similar to previous experimental observations. The simulations suggest that using contractions and expansions may be a feasible strategy for controlling LCP order and morphology in processing. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.870141
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  • 2
    Electronic Resource
    Electronic Resource
    Particle Motions in a Viscous Fluid (1980)
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Fluid Mechanics 12 (1980), S. 435-476 
    Details
    ISSN: 0066-4189
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1146/annurev.fl.12.010180.002251
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  • 3
    Electronic Resource
    Electronic Resource
    Dissolution of a Stationary Gas Bubble in a Quiescent, Viscoelastic Liquid (1975)
    s.l. : American Chemical Society
    Industrial and engineering chemistry 14 (1975), S. 175-182 
    Details
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/i160055a007
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  • 4
    Electronic Resource
    Electronic Resource
    Numerical solution of axisymmetric, unsteady free-boundary problems at finite Reynolds number. II. Deformation of a bubble in a biaxial straining flow (1989)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 1 (1989), S. 644-660 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Numerical solutions of the full Navier–Stokes equations are used to investigate the steady and unsteady deformation of a bubble in a biaxial straining flow for Reynolds numbers in the range 0≤R≤400, and Weber numbers up to O(10). The steady-state bubble shape and the frequency of small amplitude oscillations of shape are both identical for biaxial and uniaxial straining flows in the potential flow limit. However, for a large, but finite Reynolds number, the bubble shape in the biaxial straining flow is found to be fundamentally different from the shape in uniaxial flows. This is shown to be a consequence of vorticity enhancement via vortex line stretching in the biaxial flow, which does not occur in the uniaxial flow. At the highest Reynolds number considered here, R=400, the steady-state bubble behavior for low W is qualitatively similar to the potential flow case, with a limit point for existence of the low W branch of steady solutions occurring at W∼6. However, in this case a second branch of steady solutions is found for larger W≥7, which exhibits oblate bubble shapes for large W, and has no counterpart in the potential flow limit. In unsteady flows, the behavior of bubble deformation is fundamentally different in the uniaxial and biaxial flows for both high Reynolds numbers and the potential flow limit. This suggests that breakup will occur in far different ways in the two cases.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.857439
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  • 5
    Electronic Resource
    Electronic Resource
    The drag coefficient for a spherical bubble in a uniform streaming flow (1988)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 31 (1988), S. 233-237 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The drag coefficient CD=48/R for a spherical bubble in a uniform streaming flow at high Reynolds number, which was first obtained via a dissipation method by Levich [Zh. Eksp. Teor. Fiz. 19, 18 (1949)], is rederived here by direct integration of the normal stress over the bubble surface. The present study also shows that the drag coefficient up to O(R−1) depends only on the O(1) vorticity distribution right on the bubble surface, and is independent of the vorticity distribution in the fluid. Therefore the drag coefficient up to O(R−1) is completely determined by the irrotational flow solution, which is perfectly consistent with the dissipation method.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.866852
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  • 6
    Electronic Resource
    Electronic Resource
    Boundary-layer separation from a smooth slip surface (1986)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 29 (1986), S. 1360-1366 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Numerical results are presented for the streaming motion of an incompressible Newtonian fluid past axisymmetric ellipsoids of fixed shape, subject to the condition of zero tangential stress on the body surface. It is demonstrated that a substantial, closed-streamline wake appears behind the ellipsoid at moderate Reynolds numbers, O(20–50), when the ellipsoid is sufficiently nonspherical, and that this wake initially increases in size with increase of Reynolds number but then eventually decreases in size and disappears when the Reynolds number is sufficiently large, O(200–250) in our cases. The existence of streaming flow past a smooth, slip surface without separation is consistent with predictions from laminar boundary-layer theory. It is concluded that the recirculating wake that appears behind moderately deformed bubbles is strictly a finite Reynolds number phenomenon that cannot be predicted (or understood) via a boundary-layer analysis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.865701
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  • 7
    Electronic Resource
    Electronic Resource
    An experimental investigation on the stability of viscous drops translating through a quiescent fluid (1990)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 2 (1990), S. 2103-2109 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The evolution of the shape of an initially nonspherical drop translating at low Reynolds number through a quiescent fluid is investigated experimentally. It is found that the drop reverts to a spherical shape when the degree of initial deformation is small enough. However, drops that are highly deformed initially are shown to deform continuously. Specifically, a prolate drop breaks up into multiple droplets as it rises, while an oblate drop deforms into a double-emulsion drop as it translates. The experimental results agree well with results obtained earlier from numerical simulations [Phys. Fluids A 1, 1309 (1989)].
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.857796
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  • 8
    Electronic Resource
    Electronic Resource
    Vorticity transport and wake structure for bluff bodies at finite Reynolds number (1989)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 1 (1989), S. 124-131 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: This paper is concerned with the structure of recirculating wakes downstream of bluff bodies at finite Reynolds number, and the relationship between these wakes and asymptotic behavior for R→∞. It is shown that recirculating eddies at finite Reynolds number are not necessarily a precursor of the asymptotic phenomenon of separation that is "predicted'' via boundary-layer theory. In some cases, such as the flow around deformable gas bubbles, recirculating eddies may appear at intermediate Reynolds numbers, but then disappear with further increase of the Reynolds number. In other cases, recirculating eddies exist downstream of the body at finite Reynolds number that are completely detached from the body. These examples suggest that recirculating eddies at large, but finite Reynolds number do not necessarily imply anything about the solution behavior for R→∞, even for solid bodies where it is usually assumed that wakes for R∼O(10–100) are a manifestation of the same processes that lead to separation of boundary layers for R→∞.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.857540
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  • 9
    Electronic Resource
    Electronic Resource
    Numerical solution of axisymmetric, unsteady free-boundary problems at finite Reynolds number. I. Finite-difference scheme and its application to the deformation of a bubble in a uniaxial straining flow (1987)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 30 (1987), S. 1929-1940 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A brief description of a numerical technique suitable for solving axisymmetric, unsteady free-boundary problems in fluid mechanics is presented. The technique is based on a finite-difference solution of the equations of motion on a moving orthogonal curvilinear coordinate system, which is constructed numerically and adjusted to fit the boundary shape at any time. The initial value problem is solved using a fully implicit first-order backward time differencing scheme in order to insure numerical stability. As an example of application, the unsteady deformation of a bubble in a uniaxial extensional flow for Reynolds numbers is considered in the range of 0.1≤R≤100. The computation shows that the bubble extends indefinitely if the Weber number is larger than a critical value (W〉Wc). Furthermore, it is shown that a bubble may not achieve a stable steady state even at subcritical values of Weber number if the initial shape is sufficiently different from the steady shape. Finally, potential-flow solutions as an approximation for R→∞ have also been obtained. These show that an initially deformed bubble undergoes oscillatory motion if W〈Wc, with a frequency of oscillation (based on the surface tension time scale) that decreases as Weber number increases and equals zero at the critical Weber number beyond which steady solutions could not be obtained in the earlier numerical work of Ryskin and Leal [J. Fluid Mech. 148, 37 (1984)]. This clearly indicates that the point of nonconvergence of the steady-state numerical problem is, in fact, a limit point in the branch of steady-state solutions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.866207
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  • 10
    Electronic Resource
    Electronic Resource
    NONLINEAR BUBBLE DYNAMICS (1997)
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Fluid Mechanics 29 (1997), S. 201-243 
    Details
    ISSN: 0066-4189
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract The inertia-dominated dynamics of a single gas or vapor bubble in an incompressible or nearly incompressible liquid has been the subject of intense investigation for many years. Studies prior to 1976 were thoroughly reviewed by Plesset & Prosperetti (1977) in Volume 9 of this series. Our review fills the gap between Plesset & Prosperetti's review and the present. We focus on new understandings of bubble dynamics through a nonlinear dynamical systems approach.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1146/annurev.fluid.29.1.201
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