Bulletin of the American Physical Society
64th Annual Meeting of the APS Division of Fluid Dynamics
Volume 56, Number 18
Sunday–Tuesday, November 20–22, 2011; Baltimore, Maryland
Session E17: Viscous Flows |
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Chair: Howard Stone, Princeton University Room: 320 |
Sunday, November 20, 2011 4:40PM - 4:53PM |
E17.00001: The flow field of a submerged viscous impinging jet J. Tilak Ratnanather, Jung H. Kim, Anthony M.J. Davis The flow field of a submerged viscous jet impinging on an infinite plane wall is studied. The whole creeping flow of semi-infinite extent is generated via distributions on a cylindrical pipe of tangentially and normally directed Stokeslets which are modified in two stages to achieve no-slip at the wall at $z=0$. First the pressure and vorticity jumps associated with the Poiseuille flow upstream in the pipe are forced and then further distributions far upstream of the orifice at $z=h$ are added to achieve no slip on the pipe wall. The adjustment of the interior pipe flow from its upstream parabolic profile to its exit profile is thus included in this creeping flow analysis. The generated flow field for $h=1,2,3,4,5$ is used to examine the behaviour of the wall pressure and wall shear stress with respect to $h$. This behaviour is discussed briefly in the context of physiological experiments that motivated this study. [Preview Abstract] |
Sunday, November 20, 2011 4:53PM - 5:06PM |
E17.00002: Bending of Elastic Fibers in Viscous Flow: the Influence of Confinement Jason Wexler, Helene Berthet, Nawal Quennouz, Olivia Du Roure, Howard Stone, Anke Lindner Applications such as microfluidic flow sensors or living micro-organisms often involve the deformation of a slender deformable body attached to a rigid boundary. Here we investigate the deformation of an anchored elastic fiber subject to transverse flow in a microfluidic device. Our fiber protrudes into a Hele-Shaw cell, a geometry with a flow field that varies rapidly near the wall but is otherwise approximately uniform. We fabricate our fibers directly in the microchannel using a photopolymerization method. This approach allows us not only to tune the geometry of the fiber (width, length), but also to control the fiber confinement (ratio of fiber height compared to channel height). For varying flow rates we measure how the shape of the fiber changes as a function of its geometry and the confinement. We analyze our results using dimensionless analysis and discuss simplified models of the deflection. [Preview Abstract] |
Sunday, November 20, 2011 5:06PM - 5:19PM |
E17.00003: Viscous spread under an elastic lid John Lister, Jerome Neufeld, Dominic Vella We consider theoretically and experimentally the injection and axisymmetric spread of viscous fluid beneath a flexible elastic lid. In the experiments, glycerol is injected at a constant rate beneath the centre of a 1 cm thick, 50 cm diameter, soft rubber sheet laid on a rigid horizontal surface, which was prewet with an $\approx 200\mu$m thick fluid film. Measurements of the surface elevation and radial propagation are in good agreement with lubrication calculations incorporating bending stresses and gravity. Remarkably, even this simple system evolves through four asymptotic regimes with successive radial spreading laws $r\sim t^{1/6}, t^{7/22}, t^{7/12}$ and $t^{1/2}$. We determine the corresponding prefactors, and confirm the results numerically and experimentally. An alternate problem without the prewetting film is relevant to shallow geological intrusions, called laccoliths, for which we obtain yet more exotic scalings. Our analysis of tip peeling processes in these relatively simple problems gives insight that may find application in more complex problems such as cell adhesion, delamination, and the dynamics of MEMS. [Preview Abstract] |
Sunday, November 20, 2011 5:19PM - 5:32PM |
E17.00004: Study of mixing at low Reynolds number R.M. Arco, R. Zenit, E. Lauga In many mixing applications is often impossible to operate the mixer in turbulent regime due to the high viscosity of the liquid used (polymers solutions). In this study we propose a technique to induce mixing in laminar flows. A flapper is oscillated at certain frequency and the flow field around it is studied with a PIV technique. The rigidity of the flapper is varied using different materials (acrylic, neoprene). The time-reversibility of the flow was broken when the flapper became flexible. Also we used a Newtonian, and non-Newtonian fluids with elastic effects and nearly constant viscosity. All test were conducted at Re$<$0.02. Velocity profiles were measured having a impeller oscillation with $\pm$ 60 degrees from the vertical, measurement were taken in the vertical position varying the angular velocities for each impeller. Both the increase of flexibility of the impeller and the increase of the angular velocity was seen to modify the pumping capacity in both fluids. In this talk the nature of this behavior and its implications in mixing processes will be discussed. [Preview Abstract] |
Sunday, November 20, 2011 5:32PM - 5:45PM |
E17.00005: Flows in Channels with Grooves of Arbitrary Form Alireza Mohammadi, Jerzy M. Floryan Effects of small-amplitude, two-dimensional grooves on pressure losses associated with flows through channels have been analyzed. The grooves can have an arbitrary inclination with respect to the flow direction. It has been demonstrated that reduced order models of grooves' shapes provides acceptable accuracy. Use of such models permits extraction of the relevant details of geometry and formulation of general conclusions. In most cases replacement of the actual geometry with one Fourier mode of the relevant expansion produced sufficient accuracy. It is shown that the grooves' effects can be divided into those due to the change of the mean position of the wall resulting from addition of the grooves and those due to the flow modulations associated with the shapes of the grooves. The former effects can be determined analytically. The latter effects have been determined numerically using spectrally accurate discretization based on the Fourier and Chebyshev expansions. The results show strong dependence of pressure losses on the groove orientation, with the longitudinal grooves producing the smallest drag and the oblique grooves with the inclination angle of $\sim $42\r{ } exhibiting the largest flow turning potential. [Preview Abstract] |
Sunday, November 20, 2011 5:45PM - 5:58PM |
E17.00006: ABSTRACT WITHDRAWN |
Sunday, November 20, 2011 5:58PM - 6:11PM |
E17.00007: A novel release mechanism from responsive microgel capsules Hassan Masoud, Alexander Alexeev We use a mesoscale computational model for responsive gels to study the release of nanoparticles from hollow microcapsules. Our model explicitly describes the transport of nanoparticles in swelling/deswelling polymer networks with complex geometries and associated fluid flows. Our simulations show that capsule swelling results in a steady release of encapsulated nanoparticle, which is set by the ability of particles to diffuse through the capsule network. For deswelling capsules, we show that a fluid flow induced by capsule shrinking leads to rapid nanoparticle release. This release, however, is limited due to decreasing mesh size of the deswelling shell. We show that by introducing solid microrods inside deswelling capsules, we can control the rapid release. Our calculations reveal that the rods stretch the deswelling membrane and promote the formation of large pores in the shell, which allow massive flow-driven release of nanoparticles. Thus, our findings reveal a new approach for regulating the release from stimulus responsive micro-carriers that may be useful for designing new drug delivery systems. [Preview Abstract] |
Sunday, November 20, 2011 6:11PM - 6:24PM |
E17.00008: Orthogonal Boundary-Layer Flows Patrick Weidman A theoretical study is made for boundary-layer flows of different strengths intersecting each other at right angles. Analytic solutions are found for orthogonally interesecting Bickley jets, wall jets, wakes, and uniform shear flows. The equations for intersecting Blasius boundary layers and mixing layers are found and solved numerically. In all cases the development of the boundary-layer thickness for flow in the x-z plane is proportional to a fractional power of (x + z). Extensions of the work are envisioned to include plate transpiration and stretching for the wall-bounded flows. [Preview Abstract] |
Sunday, November 20, 2011 6:24PM - 6:37PM |
E17.00009: Buckling transition of a flexible fiber at a surface stagnation point Laura Guglielmini, Nicolas Autrusson, Amit Kushwaha, Eric Shaqfeh, Howard Stone The interplay of viscous and elastic stresses is relevant to a number of flow problems involving slender elastic fibers. These range from the swimming of microorganisms to the transport of pulp fibers in processing flow as well as from nanotube and nanocarpet applications to semi-flexible polymer behavior. In this work, we discuss the response of an elastic fiber tethered to a plane wall and subjected to a stagnation point flow. Using a combination of stability analysis and numerical simulations, (with the latter based on a discretized beam model), we show that, for a critical value of the ratio between viscous and elastic forces, the filament is susceptible to a buckling instability at a bifurcation point which may be subcritical. Further, we discuss the effect of thermal fluctuations on the buckling transition, thus demonstrating the dynamic effect of small fluctuations on a filament whose persistence length is much longer than its contour length. [Preview Abstract] |
Sunday, November 20, 2011 6:37PM - 6:50PM |
E17.00010: Buckling probability of an elastic fiber transported in a viscous flow of counter-rotating vortices Nawal Quennouz, Yuan N. Young, Michael Shelley, Anke Lindner, Olivia du Roure The interaction of a deformable body with a viscous flow is found in a wide range of situations ranking from biology to polymer science. Here we address the question how an elastic object transported in a viscous flow is deformed by the latter. We experimentally study the deformation and the transport of an isolated elastic fiber in a viscous cellular flow, namely a lattice of counter-rotating vortices, at low Reynolds. We have shown [1] that the fiber can buckle when approaching a stagnation point in this type of flow. The buckling threshold is determined by the relative intensity of viscous and elastic forces, the elasto- viscous number Sp. We observe that even above the threshold the fiber does not buckle each time it passes a stagnation point. We characterize the probability to buckle as a function of the Sp number for a large range of parameters (varying the flow properties, the elastic modulus, aspect ratio of the fiber and length of the fiber compared to the size of the lattice independently). We compare our experimental results to numerical simulations [2] and we discuss the origins of the differences observed. [1] E. Wandersman, N. Quennouz, Fermigier, A. Lindner and O. du Roure\textit{. Buckled in translation}, Soft Matter 6, 57155719, 2010. [2] Y.-N. Young and M. Shelley\textit{. Stretch-Coil Transition and Transport of Fibers in Cellular Flows}, PRL 99, 058303, 2007. [Preview Abstract] |
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