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  • PACS. 47.50.+d Non-Newtonian fluid flows - 61.30.Jf Defects in liquid crystals - 83.70.Hq Heterogeneous liquids: suspensions, dispersions, emulsions, pastes, slurries, foams, block copolymers, etc.  (1)
  • PACS. 83.50.-v Deformation and flow – 47.15.Fe Stability of laminar flows – 47.60.+i Flows in ducts, channels, nozzles, and conduits  (1)
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  • 1
    Electronic Resource
    Electronic Resource
    Effect of tangential interface motion on the viscous instability in fluid flow past flexible surfaces (2001)
    Springer
    The European physical journal 23 (2001), S. 533-550 
    Details
    ISSN: 1434-6036
    Keywords: PACS. 83.50.-v Deformation and flow – 47.15.Fe Stability of laminar flows – 47.60.+i Flows in ducts, channels, nozzles, and conduits
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract: The stability of linear shear flow of a Newtonian fluid past a flexible membrane is analysed in the limit of low Reynolds number as well as in the intermediate Reynolds number regime for two different membrane models. The objective of this paper is to demonstrate the importance of tangential motion in the membrane on the stability characteristics of the shear flow. The first model assumes the wall to be a “spring-backed” plate membrane, and the displacement of the wall is phenomenologically related in a linear manner to the change in the fluid stresses at the wall. In the second model, the membrane is assumed to be a two-dimensional compressible viscoelastic sheet of infinitesimal thickness, in which the constitutive relation for the shear stress contains an elastic part that depends on the local displacement field and a viscous component that depends on the local velocity in the membrane. The stability characteristics of the laminar flow in the limit of low are crucially dependent on the tangential motion in the membrane wall. In both cases, the flow is stable in the low Reynolds number limit in the absence of tangential motion in the membrane. However, the presence of tangential motion in the membrane destabilises the shear flow even in the absence of fluid inertia. In this case, the non-dimensional velocity (Λt) required for unstable fluctuations is proportional to the wavenumber k ( Λ t∼k) in the plate membrane type of wall while it scales as k2 in the viscoelastic membrane type of wall ( Λ t∼k 2) in the limit k→ 0. The results of the low Reynolds number analysis are extended numerically to the intermediate Reynolds number regime for the case of a viscoelastic membrane. The numerical results show that for a given set of wall parameters, the flow is unstable only in a finite range of Reynolds number, and it is stable in the limit of large Reynolds number.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s100510170045
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  • 2
    Electronic Resource
    Electronic Resource
    Structure and rheology of the defect-gel states of pure and particle-dispersed lyotropic lamellar phases (1999)
    Springer
    The European physical journal 12 (1999), S. 269-276 
    Details
    ISSN: 1434-6036
    Keywords: PACS. 47.50.+d Non-Newtonian fluid flows - 61.30.Jf Defects in liquid crystals - 83.70.Hq Heterogeneous liquids: suspensions, dispersions, emulsions, pastes, slurries, foams, block copolymers, etc.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract: We present important new results from light-microscopy and rheometry on a moderately concentrated lyotropic smectic, with and without particulate additives. Shear-treatment aligns the phase rapidly, except for a striking network of oily-streak defects, which anneals out much more slowly. If spherical particles several microns in diameter are dispersed in the lamellar medium, part of the defect network persists under shear-treatment, its nodes anchored on the particles. The sample as prepared has substantial storage and loss moduli, both of which decrease steadily under shear-treatment. Adding particles enhances the moduli and retards their decay under shear. The data for the frequency-dependent storage modulus after various durations of shear-treatment can be scaled to collapse onto a single curve. The elasticity and dissipation in these samples thus arises mainly from the defect network, not directly from the smectic elasticity and hydrodynamics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s100510051004
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