Bulletin of the American Physical Society
76th Annual Meeting of the Division of Fluid Dynamics
Sunday–Tuesday, November 19–21, 2023; Washington, DC
Session ZC12: Cavitation, Nucleation, Collapse, Coalescence III |
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Chair: Elias Balaras, George Washington University Room: 143B |
Tuesday, November 21, 2023 12:50PM - 1:03PM |
ZC12.00001: On the Jets Induce by a Cavitation Bubble Near a Cylinder Zhao Pan, Yuxin Gou, Junrong Zhang, Akihito Kiyama, Zhao Pan The dynamics of cavitation bubbles in the vicinity of a solid cylinder or fibre are seen in water treatment, demolition and/or cleaning of composite materials, as well as bio-medical scenarios such as ultrasound-induced bubbles near the tubular structures in the body. When the bubble collapses near the surface, violent fluid jets may be generated. Understanding whether these jets occur and predicting their directions--departing or approaching the solid surface--is crucial for assessing their potential impact on the solid phase. However, there are currently no established criteria for classifying the onset and directions of jets created by cavitation near a curved cylinder surface. In this study, we propose models to predict the occurrence and directions of jets in such scenarios, based on the non-dimensional bubble stand-off distance and the cylinder diameter. Our models are validated by comprehensive experiments. The results not only provide insights into the jetting behaviour but serve as guidelines for the design and control of jets when a cavitation bubble collapses near a cylinder, whether for protective or destructive purposes. |
Tuesday, November 21, 2023 1:03PM - 1:16PM |
ZC12.00002: Numerical simulations of an inertially collapsing gas bubble with spherical perturbations Sawyer Remillard, Mauro Rodriguez The inertial collapse of gas bubbles releases energy that can impact its surroundings which can be beneficial (lithotripsy) or unfavorable (material erosion from hydraulic cavitation). Impurities, external disturbances (e.g. acoustic waves), and/ or heterogeneities in the surrounding material will perturb the bubble interface during its collapse. Our aim is to investigate the inertial collapse of a single gas bubble with varying initial axisymmetric perturbations along the liquid-gas material interface. We initiate these perturbations to determine the amplification or dampening effect during the re-entrant jet evolution. We use the open-source Multi-component Flow Code (MFC) which solves the compressible Navier-Stokes equations using a five-equation multiphase numerical model [Bryngelson et al. Comp. Phys. Comm. (2020)]. Inertia dominates the collapse such that surface tension and phase change can be neglected. A resolution study is used to determine the mesh which captures perturbations of up to the fourth spherical harmonic mode. Considering prior Rayleigh-Plesset-type studies, we then conduct a parametric study of different initial spherical harmonic perturbations of the second and third mode. Simulation results and mode amplitudes of an initially perturbed bubble collapse near a free surface and near wall will be presented. |
Tuesday, November 21, 2023 1:16PM - 1:29PM |
ZC12.00003: Image Based Collapse Pressure Measurement of Erosive Cavitation Bubbles Fabian Reuter, Jaka Mur, Jernej Jan Kočica, Jaka Petelin, Rok Petkovšek, Claus-Dieter Ohl Cavitation erosion of hard materials such as metals is produced under certain geometric conditions when during the collapse of a single bubble a self-focusing of shockwaves amplifies the collapse. Then, already one bubble collapse is sufficient to damage the material. In this work, we non-invasively measure the pressure of erosive single bubbles within a few micrometers of the erosion site. Conventional measurements using hydrophones are not feasible due to bandwidth and geometric constraints, possible damage to equipment, and disturbing the bubble collapse at relevant distances from it. We use high-speed shadowgraphy imaging of the shockwave front with laser illumination in bursts for multiple exposures of the same shockwave front within a camera frame, allowing for a spatially and temporally resolved measurement of 2D shockwave velocity. We account for diffraction of the initially non-spherical shockwave front using an acoustic wave equation together with the shock front images. Employing an adequate equation of state of water, the local shock pressures are found. Measurements reveal that the bubble collapse pressures crucially depend on the bubble to wall distance and show the stand-off of maximum shockwave self-focusing and collapse pressures. |
Tuesday, November 21, 2023 1:29PM - 1:42PM |
ZC12.00004: Numerical simulations of cavitation bubble growth near a soft gel object Mauro Rodriguez, Jin Yang, Jonathan Estrada Biomedical therapies use focused ultrasound to treat pathogenic tissues and stones. These ultrasound waves generate cavitation bubbles that inertially grow and collapse in and near the target tissue or stone. Earlier numerical simulations have treated the bubble contents as a mixture of water vapor and non-condensable gas, but it is known that phase change affects the bubble dynamics. During bubble oscillations, the liquid evaporates into the gas bubble, water vapor condenses, and non-condensable gases dissolve into the liquid. Additionally, the nearby stone or soft gel object can affect the growth dynamics and vice versa. We conduct 3D simulations of a cavitating bubble rapidly growing near a soft (agarose) gel object 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. Simulations show wall-attached cavitation from the wall-reflected rarefaction of a nearby exploding water vapor-gas bubble. Maximum pressures and stresses in the soft gel object for varying driving bubble expansion pressure and bubble stand-off distances from the water-gel material interface are presented. |
Tuesday, November 21, 2023 1:42PM - 1:55PM |
ZC12.00005: Pressure measurement with shock wave, and liquid jet visualization of a cavitation bubble collapsing near the hard surface. Roshan Kumar Subramanian, Zhidian Yang, Francesco Romano', Olivier Coutier-Delgosha Cavitation is a well known phenomenon that occurs in the liquid when subjected to low pressure causing significant damages to the engineering systems. And, thereby affecting the system performances drastically. Many factors lead to this destruction, and out of those, two of the important elements under investigation are the generation of shock waves, and the formation of liquid jet at the end of the collapse of the cavitation bubble near the structure. This produces significant pressure on the surface of the wall leading to its damages. Many studies have been published in the literature on these aspects. But, there is still an unfamiliarity in the literature describing which of these two factors causing the dominant effect for the damage. In this study, we aim to achieve two goals to disclose this information. Firstly, we measured the pressure produced on the wall due to the impact of the bubble collapsing near to it. Then, we visualized the shock emission by using the Schlieren technique. Finally, we put together both the shock wave visualization, and the pressure measurement on the wall to clearly segregate the pressure produced by the propagating shock, and the liquid jet impact. |
Tuesday, November 21, 2023 1:55PM - 2:08PM |
ZC12.00006: Abstract Withdrawn
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Tuesday, November 21, 2023 2:08PM - 2:21PM |
ZC12.00007: Long-Pulse Laser-Induced Cavitation: A Race Between Advection and Phase Transition Xuning Zhao, Wentao Ma, Junqin Chen, Gaoming Xiang, 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. In this scenario, the causal relation between bubble dynamics and laser radiation is still unclear, complicated by the overlapping of their domains both in space and in time. In this talk, we first present a new computational model that couples multiphase fluid dynamics with laser radiation and phase transition. Key components of the model 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. Next, we explore the dynamics of pear-shaped and elongated bubbles through simulations of Ho:YAG and Thulium fiber laser experiments. The numerical results are compared with high-speed images obtained from the experiments, which yields a reasonable agreement. The temperature, pressure, and velocity fields from the simulations are analyzed to explain the bubble geometry and its impact on the delivery of laser energy. Based on the numerical results, we propose a new hypothesis that the morphing of the vapor bubble is determined by a race between advection and phase transition. To test this hypothesis, we define the speeds of advection and phase transition using a simplified model problem, and approximate their values for our simulations. This study indicates a possibility to improve laser energy delivery by designing a vapor bubble that serves as a channel (i.e., the Moses effect). |
Tuesday, November 21, 2023 2:21PM - 2:34PM |
ZC12.00008: Capillary collapse of a cavity in microgravity Karl Cardin, Christophe Josserand, Raúl Bayoán Cal An investigation of the capillary collapse of a nonspherical cavity generated by the temporary impingement of an air jet at a free liquid surface is presented. In the experiments, the collapse of the cavity takes place in a microgravity environment where the dynamics are driven by capillary forces and are not altered by gravity. Microgravity conditions are achieved by using the unique low-gravity environment of a drop tower. The collapse of a spherical cavity, an approximation for a bursting bubble at a liquid gas interface, has been well studied and is known to give rise to a liquid jet that breaks up into droplets. This investigation shows that the capillary collapse of these nonspherical cavities can also give rise to a liquid jet. The jet velocity is shown to depend on the aspect ratio of the cavity. Simulations are performed to further elucidate the cavity collapse phenomena. |
Tuesday, November 21, 2023 2:34PM - 2:47PM |
ZC12.00009: Cavitation Inception During Vortex-Vortex Interactions of Counter Rotating Vortex Pairs Steven L Ceccio, Harish Ganesh In many hydrodynamic turbulent shear flows, the weaker, stream-wise oriented vortices will cavitate before the stronger, span-wise vortices. This occurs due to stretching of the weaker vortices by the stronger vortices, which leads to a reduction in the core pressures of the weaker vortices. The stretching leads to reduced vortex core diameters and axial flow, but the relative interplay of these is still unclear. This study experimentally examines a canonical case of this vortex interaction and inception process by looking at a pair of initially parallel line vortices undergoing the Crow instability. The vortices are generated by hydrofoils whose relative arrangement can be adjusted to vary the flow properties. Measurements with high-speed Shake-the-Box PTV, high speed video, and hydrophone acoustics are taken to characterize the flow development and relate the inception properties to the underlying single phase vortex interaction. The resulting cavitation inception pressure and event rates are then related to both the flow dynamics and the freestream nuclei content. |
Tuesday, November 21, 2023 2:47PM - 3:00PM |
ZC12.00010: Ultra-Fast Micro-Actuation using Thermal Bubble-Driven Micro-Pumps Brandon Hayes, Robert MacCurdy Taking inspiration from the Mantis shrimp, we seek to develop a new class of micro-actuators for micro-robots that are both (a) ultra-fast and (b) high force. To date, these two criteria are difficult to achieve in micro-robotic actuators but have applications in both legged and winged micro-robots. In this work, we explore the use of a new class of micro-actuation technology, thermal bubble-driven micro-pumps, as an ultra-fast and high force micro-actuator. Thermal bubble-driven micro-pumps are essentially high-power thermal inkjet resistors. A current pulse heats the surface of the resistor to 300 °C in microseconds causing explosive boiling of an interfacial fluid layer which forms a high pressure (10’s atm) vapor bubble. This vapor bubble is then harnessed to perform mechanical work. When the high-power resistor is actuated, the high-pressure vapor bubble causes the thin membrane to deflect. To investigate experimentally, a stroboscopic imaging system was developed to perform high-speed imaging (2 Mfps); additionally, a Polytec laser vibrometer was used to probe the transient membrane deflection during actuation. We found that the maximum membrane deflection was 57 um and reached a maximum velocity of 15.2 m/s with a maximum acceleration of 2 x 107 m/s2. For comparison, a Mantis shrimp strike has a maximum velocity of 22.35 m/s and a maximum acceleration of 1.5 x 105 m/s2. In general, we envision thermal bubble-driven micro-pumps as a viable means to enable ultra-fast micro-actuation for micro-robotics. |
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