Bulletin of the American Physical Society
60th Annual Meeting of the Divison of Fluid Dynamics
Volume 52, Number 12
Sunday–Tuesday, November 18–20, 2007; Salt Lake City, Utah
Session KC: Drops and Bubbles IX |
Hide Abstracts |
Chair: Tim Colonius, California Institute of Technology Room: Salt Palace Convention Center 150 G |
Tuesday, November 20, 2007 8:00AM - 8:13AM |
KC.00001: Statistical equilibrium of bubble oscillations in dilute bubbly flows Tim Colonius, Rob Hagmeijer, Keita Ando, Christopher Brennen We examine statistical models for the dynamics of a dilute cloud of spherical bubbles with a distribution of equilibrium radii. For inviscid linear and nonlinear bubble oscillations, we prove the existence at large time of a statistical equilibrium and develop related expressions for the moments of the bubble radius distribution. In particular, we show that under statistical equilibrium, the bubble radius may be replaced by its period- averaged value. This leads to an enormous reduction in the number of bubbles that need to be tracked in order to compute accurate statistics. We also show that for sufficiently broad equilibrium radius distributions, timescales associated with relaxation to statistical equilibrium are short compared to physical damping associated with viscosity, heat conduction, and compressibility. This leads to a multiple-time expansion for a slowly evolving statistical equilibrium that we validate by comparing with straightforward (but time consuming) direct computations with many bubbles. [Preview Abstract] |
Tuesday, November 20, 2007 8:13AM - 8:26AM |
KC.00002: Bubble motion near a two-fluid interface. Geoffrey Curtiss, John Blake, David Leppinen, Quan Xi Wang The interaction between a cavitation bubble and the interface between two incompressible fluids of different densities is investigated. Applications abound, ranging from industrial processes involving bubble assisted mixing, to biomedical procedures for tissue damage via laser ablation techniques and gene-transfection via sonoporation. The system is investigated numerically, by means of a boundary integral approach in both exterior fluids. The code is verified by comparison with theoretical and experimental studies of the density ratios $\rho=0,1,\infty$, representative of a free surface, Rayleigh bubble and rigid boundary respectively. Small standoff distances are investigated for a range of density ratios. Results show drastic lessening of the interfacial spiking for $\rho>0.3$ in comparison to free surface motion. Bubble jetting also appears to be always in the direction of the denser fluid. For $\rho>1$ the bubble remains entrained in the depressed fluid-fluid interface throughout the collapse phase. Surface tension effects on both the bubble surface and the fluid-fluid interface are also investigated and compared to the purely inertial motion. [Preview Abstract] |
Tuesday, November 20, 2007 8:26AM - 8:39AM |
KC.00003: Applications of Sonoporation: Acoustically-Stimulated Nonspherical Collapse and Jetting of Multiple Bubbles Near a Surface Michael L. Calvisi, Qian Xi Wang, John R. Blake Nonspherical bubble collapse is a means to enhance permeability and transfect drugs and genes to cells in the process of sonoporation. In this non-invasive procedure, microbubbles injected into the bloodstream are stimulated by ultrasound, which induces nonspherical collapse and the formation of high-speed microjets directed towards the tissue surface. This jetting mechanism consequently creates a pathway for drugs or genes to enter the cellular body. The dynamics of bubble collapse are affected not only by the imposed acoustic field, but also by the properties of the bubble's surface coating, the compliance of the tissue surface, and the presence of nearby bubbles. In this talk, results from numerical models using the Boundary Integral Method are presented that help elucidate the interplay of these various factors in effecting jetting and targeted drug delivery. Numerical results are compared to recent experiments involving the acoustic stimulation of two microbubbles near a compliant surface. [Preview Abstract] |
Tuesday, November 20, 2007 8:39AM - 8:52AM |
KC.00004: Experimental study on the drag coefficient for an ellipsoidal bubble with fore-aft asymmetry Minori Shirota, Toshiyuki Sanada, Ayaka Sato, Masao Watanabe We experimentally evaluate the drag coefficient for spherical and ellipsoidal clean bubbles rising steadily in liquids of low Morton number ranging from 10$^{-11}$ to 10$^{-8}$. Four different silicone oils and super purified water are used as liquids. The shapes and rising motion of bubbles are captured by using a still camera and a high-speed video camera, respectively. The degree of fore-aft asymmetric bubble shape is quantitatively evaluated using image processing. The experimentally obtained drag coefficients are compared with those for symmetric ellipsoidal bubbles obtained analytically by Moore [J. Fluid Mech. \textbf{23}, 749 (1965)], and via numerical simulation by Blanco {\&} Magnaudet [Phys. Fluids \textbf{7}, 1265 (1995)]. The main conclusions are summarized as follows; (1) Moore's drag coefficient overestimates the experimentally obtained drag coefficient especially when bubble aspect ratio increases, (2) Blanco {\&} Magnaudet's prediction of drag coefficients for bubbles with ellipsoidal shape are also valid for those with fore-aft asymmetric shape of corresponding aspect ratio. [Preview Abstract] |
Tuesday, November 20, 2007 8:52AM - 9:05AM |
KC.00005: Re-entrant jet formation and shock emission in non-spherical bubble collapse Eric Johnsen, Tim Colonius The collapse of cavitation bubbles near a surface is a significant contributor to cavitation damage. In the present work, a high-order-accurate, quasi-conservative, interface- and shock-capturing scheme is used to simulate the collapse of a single air bubble numerically. The method allows non-spherical deformations of the interface (re-entrant jet formation) and shockwave generation and propagation. Axisymmetric Rayleigh collapse (RC) and shock-induced collapse (SIC) in a free-field and near a wall are considered in order to understand the non-spherical bubble dynamics and the sequence of emitted shockwaves; RC can be interpreted as SIC with infinite shock speed for a given pressure ratio across the interface/shock. The effects of baroclinic vorticity, acoustic radiation and interfacial instabilities are examined, and the pressure wave generated due to the impact of the jet upon the distal side is characterized. Preliminary observations show that the computed acoustic radiation is smaller for non-spherical collapse (RC near wall, free-field SIC). [Preview Abstract] |
Tuesday, November 20, 2007 9:05AM - 9:18AM |
KC.00006: The interaction of two gas bubbles with a planar shock wave Stephen Shaw, Peter Spelt, Omar Matar We consider axisymmetric and fully 3D numerical simulations of the interaction of two gas bubbles with an initially planar shock wave in water. Modelling the fluid in both phases using the compressible Euler equations together with appropriate equations of state, the resultant hyperbolic systems are solved by employing a combination of a third order ENO-Roe scheme for the spatial derivatives and a third order TVD RK scheme for the temporal derivatives. The interfaces between the different phases are tracked with a level set function in conjunction with a Ghost Fluid Method. Test results are shown to compare very well with previous work on a single bubble. The impact of the distortion of the shock front on the resultant dynamics of two bubbles is studied and its dependence on the initial shock wave strength, initial separation distance of the bubbles, and the ratio of the initial bubble radii elucidated. [Preview Abstract] |
Tuesday, November 20, 2007 9:18AM - 9:31AM |
KC.00007: Cavitation in Shear Flows Sadegh Dabiri, William A. Sirignano, Daniel D. Joseph The total-stress criterion of cavitation states that cavitation occurs when the total normal tensile stress in at least one direction exceeds a threshold value. In this study, the effect of viscous stress on the growth of cavitation bubbles in the early nucleation phase is investigated. Nucleation sites of micron size in the two cases of stagnation point flow and Couette flow are considered. The Navier-Stokes equations for multiphase flow are solved utilizing the level-set formulation. The flow properties including the bubble shape are resolved. The bubble center moves with the average velocity of the displaced fluid. For different strain rates in the flow, the threshold pressure at which the bubble becomes unstable and starts to grow is calculated. These results are important in understanding the total-stress criterion for cavitation. [Preview Abstract] |
Tuesday, November 20, 2007 9:31AM - 9:44AM |
KC.00008: Breakup of a bubble into a convergent-divergent pipe flow Jorge Peixinho, Kazuhiro Hashiguchi, Shu Takagi, Yoichiro Matsumoto We present the results of experiments study on the dynamics a bubble into a convergent-divergent pipe flow. The amplitude of the constriction and the magnitude of the flow may result in the breakup of the bubble. The occurrence of a liquid high speed jet in the direction of the flow as an initial step of the bubble breakup is reported for a large range of bubble initial sizes and flow rates. The results are compared to an impulsion model. Further, the behaviour of the bubble cloud in the slightly divergent pipe is described and the distribution in sizes of the ``daughter'' bubbles is analysed. [Preview Abstract] |
Tuesday, November 20, 2007 9:44AM - 9:57AM |
KC.00009: Airflow driven pinch-off of a bubble in a rotating liquid Raymond Bergmann, Anders Andersen, Tomas Bohr, Devaraj van der Meer We create air bubbles at the tip of a ``bathtub vortex'' which reaches to a finite depth. The ``bathtub vortex'' is induced by letting water drain through a small hole at the bottom of a rotating cylindrical container. The tip of the needle-like surface depression is unstable at high rotation rates and releases bubbles which are carried down and out through the drain-hole. Using high-speed imaging we find that the minimal neck radius of the unstable tip decreases as $R(t) \sim t^{\frac{1}{3}}$. This power law exponent signals that the air flow in the neck becomes the dominant effect over the stabilizing centrifugal forces and causes the eventual pinch-off. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700