Bulletin of the American Physical Society
65th Annual Meeting of the APS Division of Fluid Dynamics
Volume 57, Number 17
Sunday–Tuesday, November 18–20, 2012; San Diego, California
Session R10: General Instability II |
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Chair: Anne Cros, Universidad de Guadalajara Room: 25C |
Tuesday, November 20, 2012 1:00PM - 1:13PM |
R10.00001: Elasto-Capillary Coalescence of Multiple Parallel Sheets Amir Gat, Morteza Gharib We analyzed two-dimensional clamped parallel elastic sheets which are partially immersed in liquid as a model for elasto-capillary coalescence. The existing literature studied this problem via minimal energy analysis of capillary and elastic energies of the post-coalescence state. Utilizing modal stability analysis and asymptotic analysis, we studied the stability of the configuration before the coalescence occurred. Our analysis revealed previously unreported relations between viscous forces, body forces, and the instability yielding the coalescence. A mathematical description of the process creating the hierarchical coalescence structure was obtained and yielded that the mean number of sheets per coalesced region is limited to the subset $2^N$ where $N$ is the set of natural numbers. Our results were compared with experimental data and a reasonable agreement was observed. [Preview Abstract] |
Tuesday, November 20, 2012 1:13PM - 1:26PM |
R10.00002: Influence of gravity on flutter of cantilevered pipes conveying fluid Javier Rivero, Miguel Perez-Saborid We have considered the dynamics of the nonlinear interaction between a flexible pipe and the conveyed fluid in the presence of gravity. The stability of the system (fllutter and buckling) depends on parameters such as the dimensionless fluid flow rate, the gravity to bending stiffness ratio and the fluid to pipe mass ratio and it has been studied in detail both numerically and experimentally. It has also been found that the stabilizing or destabilizing effects of fluid flow depends crucially on the direction of gravity respect to the undeformed midline of the pipe. We have also computed the post-critical behavior of the system by solving the full nonlinear equations of the problem and analyzed the transfer of energy within the system in the nonlinear regime. We have formulated the problem in terms of the angles of the midline of the pipe instead of its transverse displacements, so that we can deal with large deflections without recurring to the quasi-linear approximations concerning the pipe curvature usually made in the literature. [Preview Abstract] |
Tuesday, November 20, 2012 1:26PM - 1:39PM |
R10.00003: ABSTRACT WITHDRAWN |
Tuesday, November 20, 2012 1:39PM - 1:52PM |
R10.00004: Sky dancer: the threshold of the buckling instability Anne Cros, Rodolfo Ibarra Nu\~no, Bastien Michon The sky dancer is a fabric-made large vertical tube which may ``dance'' above an air blower. We reproduced in laboratory reduced models, with diameters between 2.2 and 3 cm, and lengths varying from 45 to 95 cm. We measured the air speed and the pressure at the tube basis for the lower threshold of the tube. This threshold separates two regimes: the first one which appears for the lower velocities, when the tube falls down because of its own weight, from the second one, which corresponds to the stable regime, for which the tube stands up. Our measurements show that the air pressure thresholds get values equal to the pressure performed by the tube weight. We discuss our results and compare them with previous studies which dealt with thicker-walled tubes. [Preview Abstract] |
Tuesday, November 20, 2012 1:52PM - 2:05PM |
R10.00005: Study of Waving of grass using soap film Ravi Singh, Shreyas Mandre, Amala Mahadevan, L. Mahadevan, Mahesh Bandi Wind blowing over a grass field incites synchronized response from the grass blades, which appear as waves. This effect is called Mo-nami in a terrestrial setting, while in an aquatic setting it is termed as Ho-nami. We use a combination of experimental observations, numerical simulations and theoretical analysis to understand this effect. The experiment is conducted in two-dimensional realization of these phenomenon in a gravity driven soap film tunnel. Nylon filaments attached to the boundaries of the soap film play the role of the grass. We provide a preliminary characterization of this analog model for synchronized oscillations of grass. [Preview Abstract] |
Tuesday, November 20, 2012 2:05PM - 2:18PM |
R10.00006: ABSTRACT WITHDRAWN |
Tuesday, November 20, 2012 2:18PM - 2:31PM |
R10.00007: Vortex shedding experiments with Ekman friction Paul W. Fontana, Elizabeth Brasseale, John P. Goertz, David Raschko, Jemin Shim We present an experimental investigation of the Strouhal instability in flowing soap films. In vortex shedding by a cylinder, Roshko's formula for the one-to-one relationship between the Strouhal number $St = fD/U_\infty$ and the Reynolds number $Re = U_\infty D/\nu$ is well-established empirically and in numerical simulations. (Here $f$ is the vortex shedding frequency, $D$ is the cylinder diameter, $U_\infty$ is the upstreem flow speed, and $\nu$ is the kinematic viscosity.) However, the effect of homogeneous linear drag (Ekman friction) on the relationship has not previously been investigated. It has generally been assumed to be unimportant, but it is plausibly hypothesized to decrease the shedding frequency. If so, then ignoring drag may lead to inaccurate estimates of $Re$ based on $St$ in situations where Ekman friction is significant. We address the question with quasi-two-dimensional vortex shedding experiments in soap films in which we are able to resolve viscosity and surface friction. The results shed light on the instability mechanism of vortex shedding in particular, and they also demonstrate how precise measurement of both viscosity and surface friction is necessary to make soap film experiments useful for quantitative investigations of stability more generally. [Preview Abstract] |
Tuesday, November 20, 2012 2:31PM - 2:44PM |
R10.00008: On the dynamics of gaseous detonation in porous inert media Roman Semenko, Aslan Kasimov, Boris Ermolaev We consider a one-dimensional detonation wave propagating through a mixture of detonable gas in a porous inert medium. We assume the presence of solid metal spheres in a tube which incur the losses of the momentum and heat. The main goal of this work is to understand the role played by the losses in the structure of the steady state solutions and to analyze their linear stability. [Preview Abstract] |
Tuesday, November 20, 2012 2:44PM - 2:57PM |
R10.00009: ABSTRACT WITHDRAWN |
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