Bulletin of the American Physical Society
75th Annual Meeting of the Division of Fluid Dynamics
Volume 67, Number 19
Sunday–Tuesday, November 20–22, 2022; Indiana Convention Center, Indianapolis, Indiana.
Session T09: Bubbles: Cavitation, Nucleation, Collapse, Coalescence II |
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Chair: Mauro Rodriguez, Brown university Room: 136 |
Monday, November 21, 2022 4:10PM - 4:23PM |
T09.00001: Bubble-pair: A tool for the cell perforation and particle fragmentation Arpit Mishra, Arjun Garva, Arnab Roy, Parthasarathi Ghosh When a cavitation bubble collapses near a rigid surface, it creates a high-speed transient microjet that impinges and accelerates liquid onto the surface and produces intense mechanical shearing. An interacting bubble-pair arrangement can control the direction of these ensuing microjets, allowing for precise use in different applications. Although the shear stress caused by the collapse of a bubble has been extensively studied, the underlying dynamics of an interacting bubble-pair is less understood. Measuring these stresses in high spatial and temporal resolution is experimentally demanding and challenging; consequently, the data on bubble-induced flow fields are scarce. It is believed that the nearby surfaces and their curvature substantially influence the dynamics of collapsing bubbles. Using an axisymmetric compressible solver, we study the shear stress induced by interacting bubble-pair close to flat and curved rigid surfaces. By comparing the bubble shapes and shear stress for both surfaces, we observe that the maximum stresses are formed following the impact of the jet during its radial spreading. We expect this interacting bubble-pair arrangement may open new avenues in the field of cell perforation and be used as a tool for particle fragmentation. |
Monday, November 21, 2022 4:23PM - 4:36PM |
T09.00002: A fully compressible multi-scale model for cavitating flows Aditya Madabhushi, Krishnan Mahesh A key feature of cavitating flows is the presence of vapor over a wide range of length scales. A compressible multi-scale model that captures (a) massive vapor cavities and sub-grid bubble dynamics, (b) compressibility of the mixture medium and (c) inter-bubble interactions is developed. The homogeneous mixture of liquid and resolved vapor is tracked in an Eulerian sense and the sub-grid bubbles are tracked in a Lagrangian sense using a novel RP variant termed the ‘generalized RP equation’. Integrating the spherical momentum equation to a finite distance kR (k is a constant parameter) and combining it with the linear wave equation yields the generalized RP equation. Such an approach results in p(kR) (pressure at a finite distance from the bubble) being the external rather than p∞(pressure at infinite distance). This allows for the inter-bubble interactions to be captured via p(kR). The multi-scale model is first validated for a single resolved/unresolved bubble. Its ability to capture the inter-bubble interactions for sub-grid bubbles and the interaction between a resolved vapor cavity and an unresolved bubble are also demonstrated. It is applied to a bubble cloud exposed to a strong acoustic pulse where phenomena such as violent bubble collapse, shielding effects etc. are observed. |
Monday, November 21, 2022 4:36PM - 4:49PM |
T09.00003: Novel cavitation nuclei: Beyond particles and gas pockets Patricia Pfeiffer, Meysam Shahrooz, Marco Tortora, Carlo M Casciola, Ryan Holman, Rares Salomir, Simone Meloni, Claus-Dieter Ohl Our understanding of the origin of bubble nucleation in water is still limited. The widely accepted model is the existence of gas pockets stabilized in a hydrophobic pore, which are present on impurities or in cracks on submerged surfaces. From these pockets cavitation bubbles might explosively expand once sufficiently strong tension is applied. Interestingly, in absence of well-controlled crevices, the measured cavitation threshold is much smaller than one would expect from the classical nucleation theory. This experimental fact was mostly argued that unresolved nanoscale gaseous nuclei stabilized by some means reduce the threshold of an otherwise pure liquid. Yet, these stabilized nanobubbles acting as cavitation nuclei have not been confirmed in experiments, neither on surfaces nor in the bulk. |
Monday, November 21, 2022 4:49PM - 5:02PM |
T09.00004: Gas effects in cavitation bubbles collapse Davide Bernardo Preso, Daniel Fuster, Armand Sieber, Mohamed Farhat Since the first development of the cavitation bubbles collapse model by Lord Rayleigh, the role of the bubble content on its dynamics has aroused great interest. Despite several attempts have been made to explain the effective gas-related damping mechanisms of a collapsing bubble, the contribution of each dissipation mechanism is not yet fully understood. In this study, the dynamics of highly-spherical single cavitation bubbles generated in aqueous-ammonia solutions have been recorded over a wide range of ammonia concentrations. The comparison of experimental data with a simplified analytical model will be used to clarify the role of gas content on the various stages of the bubble collapse process. The results distinctly revealed the important influence of the dissolved gas on the bubble dynamics, as well as on its contribution to the effective damping occurring at the final collapse stage. Moreover, the simplified model allows to estimate the average bubble internal pressure from experimental results. |
Monday, November 21, 2022 5:02PM - 5:15PM |
T09.00005: Cavitation bubble induced wall shear stress at an elastic structure Hendrik Reese, Siew-Wan Ohl, Claus-Dieter Ohl Cavitation bubbles created near a rigid boundary are known to violently collapse and create jet flows onto the boundary. The thereby produced strong flows, water hammer pressure and shock waves are associated with erosion of even tough surfaces like ship propellers. In the application of ultrasound baths the created shear stress is used for surface cleaning. Despite great academic interest in bubble dynamics near a surface, the hereby created wall shear stress is difficult to measure and the erosion and cleaning mechanisms are still not fully understood. We present a study of the fluid-structure interaction between a single submillimeter sized bubble in water near an elastic structure, with focus on the stresses produced during the first oscillation cycle of the bubble. For this we developed a novel numerical solver in OpenFOAM by combining an existing fluid-structure interaction solver, which couples a linear elastic solid with an incompressible viscous fluid, with a compressible, viscous multi-component solver with phase fraction interface modeling. Numerical simulations are directly compared to experimental high-speed recordings of a laser-induced bubble near a photopolymer resin structure with particles to track the deformation. Multiple geometries are studied, including a plane elastic sheet, a cylindrical pillar and a cylindrical ring. The influence of the material elasticity on the bubble dynamics is examined. The dependence of the bubble dynamics and produced stresses on the stand-off distance is studied. |
Monday, November 21, 2022 5:15PM - 5:28PM |
T09.00006: Energy focusing and cavitation erosion during a single bubble collapse Fabian Reuter, Carsten Deiter, Claus-Dieter Ohl A cavitation bubble can focus kinetic energy of the surrounding liquid to the bubble center. A prominent effect is a violent bubble collapse with severe damage and erosion even of hardest materials. In contrary to common assumptions, we show that neither the jet that pierces the bubble during the wall-near bubble collapse, nor the ring collapse at the substrate damages hard surfaces. Instead, we demonstrate that cavitation erosion is caused by an additional energy self-focusing mechanism. This shock based self-focusing was revealed with microscopic high-speed imaging at 5 MHz framing rates combined with sub-picosecond exposure times. The correlation of in-situ and ex-situ surface damage with the location of shock-focusing proofs this novel mechanism. |
Monday, November 21, 2022 5:28PM - 5:41PM |
T09.00007: Cavitation bubble growth near an elastic object Mauro Rodriguez, Spencer H Bryngelson Gas bubbles cavitate near and erode small urinary stones during focused-ultrasound therapies. During the treatment, the bubbles oscillate due to the compressive and tensile ultrasound pressures or are attached to the stone, collapse, and impinge on its surface. During bubble oscillations, the liquid evaporates into the gas bubble, water vapor condenses, and non-condensable gases dissolve into the liquid. We conduct 3D simulations of a cavitating bubble rapidly growing near a rigid wall using the open-source Multi-component Flow Code [Bryngelson et al. Comp. Phys. Comm. (2021)]. MFC solves the 3D, compressible Navier--Stokes equations using a six-equation multiphase numerical model, including a phase change model. The solver is verified against the spherical bubble dynamics theory, including phase change. Simulations show wall-attached cavitation from the wall-reflected rarefaction of a nearby exploding water vapor-gas bubble. We also examine an ultrasound-induced oscillating bubble near an elastic object. Maximum pressures and stresses in the object for varying driving pressure, frequency, and bubble stand-off distances are presented. |
Monday, November 21, 2022 5:41PM - 5:54PM |
T09.00008: Cavitation Bubbles and Their Interactions with Granular Boundaries Armand Sieber, Davide Bernardo Preso, Mohamed Farhat We study the dynamics of a laser-induced cavitation bubble interacting with granular boundaries of different sand grain sizes. High-speed visualizations of the bubble and sand motion are performed for stand-off distances (dimensionless bubble-boundary distance) ranging between γ ≈ 5.3 and γ ≈ 0.3. Overall, we find that the presence of a nearby granular boundary leads to a bubble with a shorter lifetime and reduced centroid migration compared to a similar bubble that develops near a flat, rigid boundary. Above γ ≈ 1.3, the behavior of the bubble is nearly independent of the sand grain size. Between γ ≈ 1.3 and γ ≈ 0.6, a mound of sand forms under the bubble, forcing the latter to assume a conical shape as it collapses. The extent of the sand mound and the bubble deformation both depend on the grain size. Below γ ≈ 0.6, the bubble develops a bell-shaped form leading to the formation of thin and very fast micro-jets (vjet > 1000 m/s). Moreover, between γ ≈ 1.3 and γ ≈ 0.3, we observe granular jets erupting from the sand surface following the bubble collapse. |
Monday, November 21, 2022 5:54PM - 6:07PM |
T09.00009: Intrusive temperature measurement of the cavitation bubble collapse using cold wire Roshan Kumar Subramanian, Olivier COUTIER-DELGOSHA Cavitation is a phenomenon of rupturing the liquid when the liquid is subjected to a decrease in pressure at roughly constant temperature. Cavitation is the fundamental reason for the material erosion when the bubbles are collapsing closer to the surface. These bubbles also produce a very high temperature (thousands of degrees celsius) for a very short time (order of nano- or micro-seconds) during the collapse. Many theoretical analysis have predicted that the bubbles can raise upto few thousands of degrees celsius, and some non-invasive experimental studies using spectroscopy have shown that as well. But, to the best of our knowledge no intrusive measurement has been done to charecterize the temperature profile during the cavitation spherical bubble collapse. We have designed a cold wire sensor of the thickness of ~15 to 50 micrometers with the sensing region of 2 millimeter. These cold wires are made with kevlar or nylon fibers, titanium, nickel, silver, and silicon dioxide. The single bubble is allowed to collapse on the sensing region of the sensor, and the change in resistance is correonded to the temperature uisng the mathematical function that is callibrated prior to the experiment. The preliminary results have shown that the bubbles do raise to few thousands of degrees celsius. |
Monday, November 21, 2022 6:07PM - 6:20PM |
T09.00010: Coupling between electrohydrodynamic flow and electrostrictive cavitation in dielectric liquids under pulsed excitation Xuewei Zhang Cavitation due to electrostriction is an underlying mechanism of the electrical breakdown of dielectric liquids under nanosecond pulsed electric field. Studies have been conducted on electrohydrodynamic flows in this system resulting in negative pressure and, separately, cavitation initiation and development under negative pressure. Our work attempts to explore the coupled dynamics between the two processes. Specifically, we consider two feedback from the cavitation dynamics to the electrohydrodynamic equations. First, there is a modification of dielectric permittivity in the cavitation zone. Second, the generation and expansion of cavities can relieve negative pressure. On the other hand, the electrohydrodynamic equations links the flow characteristics with the pulsed electric field excitation. For a simple spherically-symmetric system, we show the effects of the couplings, one of which is the accelerated saturation of cavitation. Our preliminary results also suggest the possibility of controlling cavitation by adjusting the duration and ramp rate of the pulsed electric field. |
Monday, November 21, 2022 6:20PM - 6:33PM |
T09.00011: Flow of elongated bubbles in microchannels under high We conditions: cavity formation, drop encapsulation, and bubble rupture Paula Pico, Lyes Kahouadji, Assen Batchvarov, Seungwon Shin, Jalel Chergui, Damir Juric, Omar K Matar We study the dynamics of surfactant-laden elongated bubbles surrounded by liquid flowing through a rectangular microchannel under high Weber number conditions. Systems exhibiting these characteristics are found in both high-end applications of microfluidic technologies (e.g., oil recovery) and real-life environments (e.g., pulmonary airways), wherein the balance amongst inertia, viscosity, and capillarity is altered by the lower surface tension and Marangoni effects introduced by the surfactants. An increase in We or capillary number is known to gradually disturb the curvature of the bubble back until a concave re-entrant liquid cavity develops and grows towards the bubble nose. We expand on these observations by presenting a systematic characterisation of the multiple interfacial singularities that occur under these conditions, which include pinch-off and coalescence events in the liquid cavity to produce encapsulated liquid drops within the bubble and bursting of the bubble by either the liquid cavity itself or the encapsulated drops. We perform direct numerical simulations based on a hybrid interface tracking/level-set method with the account of transport and exchange of surfactants at the interface and the bulk of the liquid phase for a range of dimensionless numbers related to the flow and the surfactant adsorption/desorption kinetics. Our results suggest that the Damköhler number has a dramatic effect on the unsteady topology of the encapsulated drops-bubble compound and other characterising parameters, such as the depth of the re-entrant cavity and the drop size. The numerous phenomena involved in the system include: i) cavity formation without drop encapsulation events; ii) drop encapsulations with subsequent stabilisation of the bubble back; and iii) drop encapsulations that result in highly distorted bubble-liquid interfaces. |
Monday, November 21, 2022 6:33PM - 6:46PM |
T09.00012: Particulate Projectiles Driven by Cavitation Bubbles Zibo Ren, Zhigang Zuo, Shengji Wu, Shuhong Liu The removal of surface-attached particles with cavitation bubbles is usually attributed to the jetting or shear stresses when bubbles collapse. In this work, we report an unexpected phenomenon that millimeter-sized spherical particles made of heavy metals (e.g., stainless steel), when initially resting on a fixed rigid substrate, are suddenly accelerated like projectiles through the production of nearby laser-induced cavitation bubbles of similar sizes. We show experimentally and theoretically that the motion of a particle with radius Rp is determined by the maximum bubble radius Rb,max, the initial distance from the laser focus to the center of the particle L0, and the initial azimuth angle φ0. We identify two dominant regimes for the particle's sudden acceleration, namely, the unsteady liquid inertia dominated regime and the bubble contact dominated regime, determined by Rb,maxRp=L02. We find the nondimensional maximum vertical displacement of the particle follows the fourth power and the square power scaling laws for respective regimes, which is consistent with the experimental results. Our findings can be applied to nonintrusive particle manipulation from solid substrates in a liquid. |
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