Bulletin of the American Physical Society
63rd Annual Meeting of the APS Division of Fluid Dynamics
Volume 55, Number 16
Sunday–Tuesday, November 21–23, 2010; Long Beach, California
Session HQ: Bubbles II |
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Chair: Pengtao Yue, Virginia Polytechnic Institute and State University Room: Long Beach Convention Center 203B |
Monday, November 22, 2010 10:30AM - 10:43AM |
HQ.00001: Tip vortex cavitation suppression by water ejection from wing tip Mohamed Farhat, Martino Reclari In the present study we investigated how a water jet, used to create a winglet-like effect, actively reduces or suppress the cavitation formed into the core of a tip vortex. Modifications of the vortex structure were monitored by measuring the velocity profiles with laser Doppler velocimetry. High-speed jets proved to be very effective in increasing the size of the vortex core, thus inhibiting the formation of tip vortex cavitation. [Preview Abstract] |
Monday, November 22, 2010 10:43AM - 10:56AM |
HQ.00002: Tip vortex cavitation suppression by mass injection Harish Ganesh, Natasha Chang, Steven Ceccio Injection of water and aqueous polymer solutions in to the core of a trailing vortex is found to delay the onset of tip vortex cavitation (TVC). For the case without any mass injection, cavitation inception ($\sigma _{I}$= 3.3) occurred at a substantially higher pressure (-C$_{pmin}$= 2.3) than that was expected based on the mean vortical flow. Mass injection (both water and polymer) into the vortex core led to a reduction in the inception pressure. 2-D Particle Image Velocimetry was performed in a region of flow in the vicinity of the average inception location near the hydrofoil tip to determine the instantaneous flow fields near the vortex core. Mass injection led to significant modification of the unsteady flow field, while the average flow field was not strongly affected. A 50{\%} reduction in RMS velocities in comparison with the non-injection conditions was observed for the case of polymer injection, the case of maximum cavitation suppression. Cavitation inception/desinence studies were conducted for different mass and momentum fluxes to develop a hypothesis for TVC suppression. [Preview Abstract] |
Monday, November 22, 2010 10:56AM - 11:09AM |
HQ.00003: Inviscid Partial Coalescence from Bubbles to Drops F.H. Zhang, P. Taborek, J. Burton, B.C. Khoo, K.M. Lim, S.T. Thoroddsen Coalescence of bubbles (drops) not only coarse the bubble (drop) sizes, but sometimes produces satellite bubbles (droplets), known as partial coalescence. To explore links between the drop and bubble cases, we experimentally study the partial coalescence of pressurized xenon gas bubbles in nano de-ionized water using high-speed video imaging. The size of these satellites relative to their mother bubbles is found to increase with the density ratio of the gas to the liquid. Moreover, sub-satellite bubbles are sometimes observed, whose size is also found to increase with the density ratio, while keeps about one quarter of the primary satellite. The time duration from start of the coalescence to formation of the satellites, scaled by the capillary time, increases with the density ratio too. In addition, as the size ratio of the father bubble to the mother bubble increases moderately, their coalescence proceeds faster and the sub-satellite is prone to form and relatively larger. [Preview Abstract] |
Monday, November 22, 2010 11:09AM - 11:22AM |
HQ.00004: Contact time of a pair of bubbles in an acoustic field Minori Shirota, Hiroki Miyamae Contact time of a pair of bubbles in an acoustic field is investigated experimentally. Pairs of bubbles of about 0.1 mm in radius were exposed in an acoustic field of about 30 kHz. The bubbles were generated at T-shaped microfluidic junction in silicone oil of 50 cSt with actively controlled gas pressure change. These bubbles were then introduced into an acoustic levitator commonly used in single bubble sonoluminescence experiment. The contact time of the oscillating bubbles were quantitatively evaluated using high-speed imaging technique. Bubbles with in-phase volume oscillation attracted each other due to secondary Bjerknes force and finally coalesced. We observed bubbles smaller than resonant sizes at large separate distance deforms greatly and coalesced immediately when they touch, while bubbles of the resonant sizes were kept contacting such long time as over 100 periods of forcing. [Preview Abstract] |
Monday, November 22, 2010 11:22AM - 11:35AM |
HQ.00005: Collisions between a rising bubble and a rigid sphere A. Belmonte, S.T. Thoroddsen Motivated by studies of particle sedimentation in bubbly turbulence, we perform an experimental study of the controlled collision between a rising bubble and a rigid sphere. Both stationary and sinking spheres are considered. Impact dynamics including bouncing are measured as a function of relative sizes, collision velocity, buoyancy, surface tension, and the viscosity of the continuous phase. High-speed video imaging is used to measure the bubble deformations and the induced capillary waves. We estimate the effective coefficient of restitution of the collision and compare to recent models for bubbly sedimentation. [Preview Abstract] |
Monday, November 22, 2010 11:35AM - 11:48AM |
HQ.00006: The rupture dynamics of ultra-viscous bubbles James Bird, Howard Stone, John Bush When air bubbles rise to the surface of a liquid, they create a thin-film dome that eventually ruptures. In liquids with relatively low viscosity, the rupture dynamics are dominated by surface tension and inertia and typically occur over a period of milliseconds. In liquids with relatively high viscosity, the viscous dissipation slows the dynamics enough that gravity, rather than surface tension, is believed to be responsible for the bubble collapse. However, here we demonstrate that gravity is responsible for neither the collapse nor the resulting instability that wrinkles the film. Using a combination of experiments and theory, we investigate why capillary forces display attributes that are normally exclusive to gravitational forces. [Preview Abstract] |
Monday, November 22, 2010 11:48AM - 12:01PM |
HQ.00007: Singular jets in the formation of bubbles in viscous fluids Thomas Seon, Virginie Duclaux, Arnaud Antkowiak We study experimentally the process of formation of large bubbles in viscous fluids. Whereas at low flow rates, the produced individual bubbles quickly recover a quasi-spherical shape, collective behaviors between bubbles are identified as the feeding gas flow rate is increased. These interactions may lead to the surprising gobbling of a bubble by another, resulting in large sized bubbles with inner viscous shells. At even higher feeding rates, a violent Worthington jet following bubble pinch-off appears. This jet is so intense and concentrated that perforation of the bubble may occur. We analyze the whole phenomenology of the large interface deformations associated with bubble formation in viscous fluids with detailed experiments conducted with high-speed video imaging. [Preview Abstract] |
Monday, November 22, 2010 12:01PM - 12:14PM |
HQ.00008: Marginal Pinching in a Bubble Sitting on a Solid Surface Guillaume Berteloot, Pirouz Kavehpour, Pooriah Sharif-Kashani While the shape of a bubble is widely understood to be dictated by a competition between film elasticity and Laplace pressure induced by the curvature of the latter, the shape of the liquid film in contact with the solid surface has not been studied. Using fluorescence microscopy techniques, we show that the inner liquid/air interface exhibits a dip. This can be related to marginal pinching, and simulations shows good agreement between theory and experiment. This dip depends on the surfactant used for bubble formation, and the height difference increases with time. This feature can be of importance, because bubbles can be seen as a base unit for foams, which are widely used for medical as well as industrial purposes, such as enhanced oil recovery. For those applications, the interaction between the foam and the substrate is crucial, as the quality of the foam hence the efficiency of the process depends on it. The study of foams can be applied to bubbles as one can see the vicinity of the contact line as part of a Plateau border. [Preview Abstract] |
Monday, November 22, 2010 12:14PM - 12:27PM |
HQ.00009: Explosion-Induced Implosions of Cylindrical Shell Structures C.M. Ikeda, J.H. Duncan An experimental study of the explosion-induced implosion of cylindrical shell structures in a high-pressure water environment was performed. The shell structures are filled with air at atmospheric pressure and are placed in a large water-filled pressure vessel. The vessel is then pressurized to various levels $P_{\infty} =\alpha P_c$, where $P_c$ is the natural implosion pressure of the model and $\alpha$ is a factor that ranges from 0.1 to 0.9. An explosive is then set off at various standoff distances, $d$, from the model center line, where $d$ varies from $R$ to $10R$ and $R$ is the maximum radius of the explosion bubble. High-speed photography (27,000 fps) was used to observe the explosion and resulting shell structure implosion. High-frequency underwater blast sensors recorded dynamic pressure waves at 6 positions. The cylindrical models were made from aluminum (diameter $D = 39.1$~mm, wall thickness $t = 0.89$~mm, length $L = 240$~mm) and brass ($D = 16.7$~mm, $t = 0.36$~mm, $L=152$~mm) tubes. The pressure records are interpreted in light of the high-speed movies. It is found that the implosion is induced by two mechanisms: the shockwave generated by the explosion and the jet formed during the explosion-bubble collapse. Whether an implosion is caused by the shockwave or the jet depends on the maximum bubble diameter and the standoff distance. [Preview Abstract] |
Monday, November 22, 2010 12:27PM - 12:40PM |
HQ.00010: Single cavitation bubble dynamics in micro-channels near free and rigid boundaries Oscar Enriquez, Devaraj van der Meer, Detlef Lohse, Claus-Dieter Ohl It is well known that cavitation bubbles jet towards a rigid interface and away from a free surface. Yet, cavitation bubbles between a free and a rigid boundary show more complex deformation and the direction of jetting depends on a delicate interplay of attractive and repulsive forces. We re-investigate this regime in the context of microfluidics. We use laser-induced cavitation bubbles and high-speed photography to study their dynamics. The cavitation bubble is located between two channel walls ($500 \mu m$ apart) and a free surface. We vary the distance of both the free interface and the bubble from the walls. In most of the parameter space we observe the expected dynamics. Yet, between these scenarios we find jetting directed towards the liquid-air interface as well as axisymmetric collapse without a jet. Additionally, we find complex dynamics of the free interface. [Preview Abstract] |
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