Bulletin of the American Physical Society
77th Annual Meeting of the Division of Fluid Dynamics
Sunday–Tuesday, November 24–26, 2024; Salt Lake City, Utah
Session X07: Bubbles: Cavitation, Nucleation, Growth and Collapse |
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Chair: Kevin Wang, Virginia Tech Room: Ballroom G |
Tuesday, November 26, 2024 8:00AM - 8:13AM |
X07.00001: Laser-induced Cavitation in Extreme Thermal Conditions Tariq Alghamdi, Peter Taborek, Kenneth R Langley, Andres A Aguirre Pablo, Sigurdur T Thoroddsen Ultra-high-speed video imaging is utilized to track cavitation bubble dynamics in liquid helium, at frame rates of up to 7 million frames per second. Cavitation is induced by focusing a 532 nm pulsed Nd-YAG laser at a spot with a minimum spot size of 150 μm and pulse duration of 6 ns, creating a high-pressure plasma that initiates the formation of a rapidly expanding bubble/void, followed by its collapse. Detailed description of our optical-access cryogenic setup is outlined in N. Speirs, PRF (2020). The setup utilizes four windows for different functions: illumination, image capture, laser beam transmission, and laser beam focusing via a parabolic mirror to induce cavitation. By using liquid Helium we span cavitation dynamics over a full range of extreme thermal conditions, from 1.2 K, where helium behaves as a superfluid, to T > 5K where we reach super-critical conditions. The influence of ambient pressure on the bubble dynamics is examined, along with the observed shock waves. A comparison between experimental results and a non-thermal bubble model is presented. The pressure field surrounding the bubble is estimated analytically, and irregular patterns on the bubble surface are visualized and discussed wrt nucleation theory. |
Tuesday, November 26, 2024 8:13AM - 8:26AM |
X07.00002: Cavitation and shock waves in shear-thickening fluids Pragya Patel, Guillaume Thomas Bokman, Armand Sieber, Bratislav Lukic, Emile Pecquet, Rafael R Cerro, Outi Supponen Shear thickening fluids (STFs) exhibit a dramatic increase in viscosity when exposed to high strain rates, making them ideal candidates for protective equipment and industrial damping systems. Although numerous studies have shown that the addition of STFs to Kevlar fabrics and foams improves shock absorption, there is still little experimental data on shock wave propagation, cavitation nucleation and dynamics, and crack propagation in these fluids. Visualizing such phenomena with conventional imaging techniques is difficult due to the small spatio-temporal scales of the processes and the opacity of many shear-thickening media. We therefore separately investigate the dynamics of single, laser-induced cavitation bubbles in optically transparent STFs with high-speed visible light imaging and the propagation of shock waves in opaque STFs impacted by high-energy shocks with high-speed phase-contrast X-ray imaging. Initial results indicate that the collapse of a single bubble in STFs is less damaging to a neighbouring wall compared to water and that cavitation bubbles nucleate after the passage of a shock wave through STFs. |
Tuesday, November 26, 2024 8:26AM - 8:39AM |
X07.00003: Modeling and Analysis of Non-spherical Vapor Bubbles Induced by Long-Pulsed Laser: A Race Between Advection and Phase Transition Xuning Zhao, Junqin Chen, Pei Zhong, Kevin Wang Non-spherical vapor bubbles of complex geometry (e.g., elongated cone, “pear-like” shape, etc.) are often observed in applications that operate long-pulsed laser in a liquid environment. However, understanding the formation mechanisms of these non-spherical shapes and their relation to laser settings remains challenging. In this talk, we introduce a new computational model that couples multiphase fluid dynamics with laser radiation and phase transition. Key components include an embedded boundary method for solving the laser radiation equation on the same “fluid mesh”, a method of latent heat reservoir for predicting laser-induced vaporization, a local level set method for interface tracking, and the FIVER (FInite Volume method with Exact multi-material Riemann solvers) method for enforcing interface conditions. We then investigate the dynamics of pear-shaped and elongated bubbles through simulations of Ho:YAG and Thulium fiber laser experiments. The predicted bubble nucleation and morphology agree reasonably well with the experimental observation. The full-field results of laser irradiance, temperature, velocity, and pressure are analyzed to explain bubble geometry and energy transmission. Based on the numerical results, we propose a new hypothesis that vapor bubble morphing is determined by a race between advection and phase transition. To test this, we define the speeds of advection and phase transition using a simplified model problem and approximate their values for our simulations. The results support the hypothesis. This study indicates a possibility to improve laser energy delivery by designing vapor bubbles that serves as a channel (i.e., the Moses effect). |
Tuesday, November 26, 2024 8:39AM - 8:52AM |
X07.00004: Controlling Long-Pulsed Laser-Induced Cavitation Through Nanoparticle Doping: A Numerical Analysis Xuning Zhao, Qingsong Fan, Po-Chun Hsu, Kevin Wang Previous studies indicate that the medium's laser absorption coefficient () influences laser energy transmission and fluid/bubble dynamics in long-pulsed laser-induced cavitation. However, few studies explore the strategies to change the medium’s and the resulting impacts on the dynamics and transmission. In this talk, we present an experimental method in which the absorption coefficient of water is modified by introducing PEDOT nanoparticles, achieving a range from 2.6 to 31.3 for the Holmium: YAG laser as concentration increases from 0% to 1 wt.%. We then conduct numerical simulations for laser-induced cavitation with seven selected absorption coefficients within this range to explore the effect of varying . These simulations utilize a new computational model that couples multiphase fluid dynamics with laser radiation and phase transition (vaporization). The simulated bubble evolution aligns well with experimental results in water with 0% PEDOT. Results indicate that increasing leads to earlier bubble nucleation (16.4 vs. 4.4 s) and a transition from round to long, conical bubble shape, with lower temperature observed inside the conical vapor bubble. Moreover, the impact on laser energy transmission highly depends on the distance from measurement position to the laser source. At shorter distances (≤0.25 mm), higher enhances energy delivery due to the Moses effect, while at longer distances (≥1.5 mm), lower is more effective in reducing energy absorption. In intermediate ranges, energy transmission shows a non-linear relationship with increasing . |
Tuesday, November 26, 2024 8:52AM - 9:05AM |
X07.00005: Vibrational interaction of two vapor-rich microbubbles in degassed water Kyoko Namura, Xuanwei Zhang, Ryu Matsuo, Motofumi Suzuki In this study, we clarify the change in vibration frequency due to the vibrational interaction between two self-oscillating microbubbles. When degassed water is locally heated, a vapor-rich bubble of about 10 μm in diameter is generated above the heat source. This bubble can generate flows of up to 1 m/s and are therefore expected to be used as micropumps [1]. The vapor-rich bubbles self-oscillate at a stable frequency for a long period of time because of intense evaporation and condensation cycles on the local heating point. In this study, two bubbles are generated simultaneously by irradiating two laser spots on a photothermal conversion thin film. The distance between the two laser spots is systematically varied using a spatial light modulator. Then, a 5 Mfps high-speed camera is used to capture the change in bubble oscillation as a function of the distance between the two bubbles. When the distance between the bubbles is varied without changing the laser intensity, the frequency of the bubbles varies from 0.5 to 0.8 MHz depending on the distance between the bubbles. Particularly when the distance between the bubbles is close, the bubbles' oscillations is counterphase-synchronized. This coupled behavior is well reproduced by the extended Rayleigh-Plesset model, which incorporates pressure interactions. |
Tuesday, November 26, 2024 9:05AM - 9:18AM |
X07.00006: Cavitation inception during the interaction between a pair of counter-rotating vortices Aditya Madabhushi, Krishnan Mahesh We perform Large-Eddy Simulation (LES) to study the interaction between a pair of unequal strength counter-rotating vortices in the wake of two hydrofoils at Re = 1.7 x 106 (same experimental conditions as reported in Knister et. al., 2020). Crow instability develops on the weaker vortex beyond one chord length (x/c ~ 1.0) downstream of the trailing edge, causing it to stretch and wrap around the stronger vortex. p < pv (p - pressure, pv - saturated vapor pressure) occurrences in the weaker vortex are spatially and temporarily intermittent, predominantly occurring between x/c: 1.1 - 1.5. The largest drop in its core pressure occurs in the regions where the cores are closest to each other. Probability distribution functions reveal that only a small part of the weaker vortex experiences p < pv. A dynamic process of increase in mean (spatially averaged) axial stretching followed by core pressure reduction is observed in the weaker vortex. The axial stretching is spatially non-uniform, resulting in a non-uniform distribution of pressure along its axis. The impact of axial stretching, initially localized, spreads along the vortex axis during the later stages of the Crow cycle resulting in more regions having lower pressure. |
Tuesday, November 26, 2024 9:18AM - 9:31AM |
X07.00007: Cavitation upon impact: flow and bubble formation upon the underwater interaction of two objects Akihito Kiyama, Shota Imai, Donghyuk Kang Water may form bubbles when it is subject to a change in pressure (i.e., cavitation). It is known to cause rapid volume change, resulting in not only damage to the surface but also the possible application in beneficial ways. Cavitation may be introduced using acoustic pressure waves or a high-speed flow. Moreover, there are various simple ways to cavitate water without using expensive equipment. Bubbles can form when we strike a water-filled bottle (Pan et al., PNAS, 2017), or when a popper snaps to impact the underwater substrate (Kiyama et al., PRFluids, 2024), or when a sphere impacts the substrate (e.g., Seddon et al., EPL, 2012). We are interested in the detailed flow field and the cavitation process upon the underwater impact, where an object can be accelerated fast enough to cavitate water by simply striking it. We report our recent status on the attempt to understand how cavitation phenomena upon impact are related. We employ the particle tracking method to try to capture the overall flow patterns during this event to understand this transient process with the help of some simple theoretical considerations. |
Tuesday, November 26, 2024 9:31AM - 9:44AM |
X07.00008: Particle Tracking in X-Ray and Optical Imaging for Cavitation Inception Studies on Rough Wall Surfaces Sanjay Vasanth Kethanur Balasubramaniam, Samyukta Suman, Swathiga Devi Chandrasekaran, Olivier COUTIER-DELGOSHA The dynamics of the flow leading to cavitation inception with a rough wall are investigated in a cavitation tunnel with a convergent-divergent section. Two types of measurement techniques, ultra-fast synchrotron X-ray imaging and optical imaging, are employed to acquire data on cavitation inception. The study aims to understand the effect of the free-stream nuclei population on inception and the flow dynamics leading to inception by seeding the flow. The diverging section of the Venturi is laser-etched to induce roughness varying from smooth (~3-5 micrometers) to rough (~100 micrometers). The etching geometry represents a checkerboard pattern to maintain consistent flow physics. Image processing techniques using machine learning are used to segment and track the particles in the flow field. Migration behavior is observed in the microbubbles generated from the breakup of incipient cavitation bubbles, leading to inception events, which aligns with previous studies. Particle tracking methods are used to further understand this phenomenon. The production of these microbubbles and the percentage that initiate cavitation events are investigated for various roughness cases. |
Tuesday, November 26, 2024 9:44AM - 9:57AM |
X07.00009: Comparative Analysis of Optical and X-ray imaging Techniques for Cavitation Inception Samyukta Suman, Sanjay Vasanth Kethanur Balasubramaniam, Swathiga Devi Chandrasekaran, Olivier COUTIER-DELGOSHA Curved surfaces like propeller blades are prone to cavitation, a phenomenon that causes structural damage. In this study, comparison of high-speed optical imaging and X-ray imaging for small scale cavitation in a dynamic flow is investigated. A high-speed camera is used for obtaining inception locations on the divergent of a venturi type section with various roughness ranging from 3 to 110 micrometers. Factors such as inceptions points, efficient tracking of the nuclei, information about gaseous and liquid phases, void fraction measurement and cavitation bubble collapse, are studied between X-ray and optical imaging techniques. This will help us provide more insight into the flow field structure and its dynamics. With exceptional spatial and temporal resolution in X-ray imaging, visualization of inception for various roughness will help us study quality of cavitation bubbles and boundary layer dynamics. The findings from this study will help us examine the trade-offs between experimental complexity, depth of information and multi-scale analysis for different imaging techniques for inception flow. |
Tuesday, November 26, 2024 9:57AM - 10:10AM |
X07.00010: Impacts of Surface Roughness on Cavitation Inception and Flow Dynamics Swathiga Devi Chandrasekaran, Sanjay Vasanth Kethanur Balasubramaniam, Samyukta Suman, Olivier COUTIER-DELGOSHA Cavitation inception on a Venturi-type test section is investigated, using a small-scale water tunnel. High-speed imaging, combined with continuous back-lit illumination, is used to capture the microbubble formation on the diverging section of the test model. This study is pivotal for understanding the impacts of surface roughness on the location and dynamics of cavitation inception. The model’s diverging part, measuring 51.6 mm in length and 5 mm in width, is etched in the checkered pattern. The laser etching technique is utilized to obtain varying surface roughness ranging from 4 to 100 micrometers. The visualizations of the flow fields around the test model are analyzed using image processing techniques to identify the impact of roughness on the location of cavitation inception, as well as the dynamics of microbubbles produced by each cavitation bubble collapse. The presence of different roughness affects the cavitation process, by shifting the inception location and altering the flow dynamics. |
Tuesday, November 26, 2024 10:10AM - 10:23AM |
X07.00011: Experimental investigation of shock wave and microjet effects on wall pressure induced by two cavitation bubbles. Roshan Kumar Subramanian, Olivier COUTIER-DELGOSHA Cavitation has been a subject of scientific interest since Euler first discussed it in 1754 within his turbomachinery theory. The fascination intensified in the early 1900s when researchers observed that cavitation, which involves the formation of bubbles in a liquid under pressures below the saturated vapor pressure, significantly impacts performance in hydrodynamic systems like marine propellers and pumps, primarily through material erosion. The collapse of these bubbles generates shock waves and microjets, leading to ongoing debates about which phenomenon is more damaging. Our research has established that shock waves are the primary mechanism of damage in hydrodynamic systems with rigid boundaries. This conclusion is based on a precise correlation between the pressure produced and the timing of the shock impact from a single bubble collapsing near a rigid wall. To our knowledge, this precise experimental demonstration of shock impact timing has not been achieved before. Since bubbles usually appear in clusters within hydrodynamic systems, understanding their interactions is crucial. We are currently investigating the dynamics of two bubbles by varying their separation distance and size, and visualizing the resulting shock waves, and microjets. This research aims to elucidate how the presence of another bubble affects dynamics and pressure on nearby rigid walls, thereby enhancing our understanding of cavitation erosion mechanisms. |
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