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 J09: Bubbles: Cavitation, Nucleation, Collapse, Coalescence I |
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Chair: Hector Gomez, Purdue University Room: 136 |
Sunday, November 20, 2022 4:35PM - 4:48PM |
J09.00001: Cavitation in a soft porous material Hector Gomez, Yu Leng, Ruben Juanes, Pavlos P Vlachos We study the collapse and expansion of a cavitation bubble in a deformable porous medium. We develop a continuum-scale model that couples compressible fluid flow in the pore network with the elastic response of a solid skeleton. Under the assumption of spherical symmetry, our model can be reduced to an ordinary differential equation that extends the Rayleigh-Plesset equation to bubbles in soft porous media. The extended Rayleigh-Plesset equation reveals that finite-size effects lead to the breakdown of the universal scaling relation between bubble radius and time that holds in the infinite-size limit. Our data indicate that the deformability of the porous medium slows down the collapse and expansion processes, a result with important consequences for wide-ranging phenomena, from drug delivery to spore dispersion. |
Sunday, November 20, 2022 4:48PM - 5:01PM |
J09.00002: Effect of gas content on cavitation nuclei in a Gibbs Free Energy framework Karim Alame, Krishnan Mahesh A Gibbs free energy approach is proposed to model cavitation inception. The model is general for homogeneous and heterogeneous nucleation. The variation in gas content, largely ignored in the literature, is explored using an ideal gas law. Its effect on cavitation inception is studied. It is found that the gas content stabilizes nuclei formation and reduces the energy barrier for nucleation. Hysteresis between the incipience and desinence event can also be explained. An analytic solution relating the initial bubble diameter to the critical pressure is derived, as opposed to the standard methods that have relied on calculating it numerically. A model for the rate of the cumulative nuclei histogram with respect to bubble diameter is proposed. The model recovers the $-4$ power law observed experimentally. |
Sunday, November 20, 2022 5:01PM - 5:14PM |
J09.00003: Experimental study of a laser-induced cavitation bubble Charles Fort, Philippe M Bardet Measurement of the mass transfer around a cavitation bubble is particularly challenging due to the small spatial and temporal scales involved. We built a dedicated modular octagonal chamber that can be pressurized while offering optical access for imaging and laser light delivery. Here, we use the non-intrusive laser-induced fluorescence of a dye to probe the flow dynamics around a laser-induced cavitation bubble. By choosing an appropriate dye sensitive to O2 quenching, we can directly assess the mass transfer around the growing cavitation bubble with a high-speed CMOS camera. |
Sunday, November 20, 2022 5:14PM - 5:27PM |
J09.00004: Fast X-ray imaging of the onset of ultrasonic horn cavitation Luc Biasiori-Poulanges, Claire Bourquard, Bratislav Lukic, Ludovic Broche, Outi Supponen High-power ultrasonic horns operating in liquids at low frequency are known to generate a cone-shaped cavitation bubble cloud, for which the early stages of the cavitation activity remain elusive. In this presentation, the cavitation inception and the mechanisms resulting in the cone formation are addressed using high-speed synchrotron X-ray radiography. Radiographs reveal a 3-step process. Few microseconds after the sonication starts, several single cavitation bubbles are produced on the horn surface and oscillate. These bubbles then generate individual clouds under a splitting process combined with a lens effect induced by the interface curvature of each initial bubble and the vapor-to-liquid sound speed ratio. Finally, the clouds merge to form a larger cone-shaped bubble cloud. While experiments are conclusive to solely elucidate steps 1 and 3, we complement the description of step 2 using geometrical acoustics where the bubble is modeled as a plano-convex lens. Qualitative descriptions are complemented with quantitative measurements, such as the nuclei relaxation time and the bubble size distribution closely beneath to the horn tip, which are usually penalized by the integration along the line-path when using conventional shadow-based imaging. |
Sunday, November 20, 2022 5:27PM - 5:40PM |
J09.00005: Effects of gas concentration on cavitation dynamics in a venturi channel Hongseok Choi, Hyungmin Park Various aspects involved in the cavitation have been studied for a long time, but due to the difficulty of measuring the velocity fields of a very-fast-occurring flow phenomena, the interaction between the flow and cavitation is not fully understood. We conducted an experiment in the 2D venturi channel, focusing on the evolution of cloud cavitation, under the lowered background pressure (to 0.5 atm) to create conditions for cavitation to occur even at relatively low flow rates. The cavitation bubble formation and the flow field were measured using shadowgraphy, PTV, and PIV at Re = 100,000-131,500. In addition, the amount of dissolved gas in the water flow was controlled through the injection and removal of air in the test section. We found that the amount of cavitation bubble generation increased as the amount of dissolved gas increases, but the point at which cavitation pattern transition from the sheet to cloud was rather delayed. Also, the volumetric growth of cloud cavitation also decreased as the gas content increases. We will further the analysis of the mechanism of cavitation control with the gas concentration, together with the flow field measurements. |
Sunday, November 20, 2022 5:40PM - 5:53PM |
J09.00006: Shock-Induced Cavitation Inside Droplets Jose Rodolfo Chreim, Tim Colonius Droplet aero-breakup is a complex phenomenon that yields a rich set of interface and hydrodynamic instabilities and potentially cavitation, especially when breakup is initiated by shock waves. Depending on the incident-shock intensity, internally reflected expansion waves form regions of metastable liquid that cavitate and couple to the droplet dynamics. Previous studies investigated the effects of the vapor cavity size and position on the droplet overall morphology and movement as well as the evolution of wave structures in the liquid region. An investigation on early-stage cavitation induced by shock waves is nonetheless missing. We present results of the interaction between a shock wave and a water droplet, focusing on early-stage cavitation. Simulations are carried out on MFC, a multi-component, multi-phase, bubbly compressible flows open-source tool. The homogeneous part of the 6-equation mixture model is solved by a flux-splitting approach and an explicit TVD RK time-marching scheme. HLLC- approximate Riemann solvers are used with proper correction for the quasi-conservative form of the equations and a high-order WENO scheme reconstructs the primitive variables. The nonhomogeneous part is solved by enforcing infinitely fast mechanical, thermal, and chemical relaxation procedures. |
Sunday, November 20, 2022 5:53PM - 6:06PM |
J09.00007: The characteristics of bubbly shock waves in a cavitating venturi via time-resolved X-ray densitometry Udhav U Gawandalkar, Christian Poelma Partial cavitation is a common form of cavitation, where unstable attached vapour cavities are formed and shed periodically, leading to cloud cavitation. Classically, it was believed that a periodically generated re-entrant jet at cavity closure, travelling upstream below the vapour cavity solely is responsible for the cloud cavitation. However, studies show that bubbly shock waves or condensation shock waves emanating from the periodic collapse of a relatively large cavitation cloud is an alternate mechanism that can cause cavity detachment. To this end, the flow conditions that favour the formation of such condensation shock waves remain less explored in the literature. Hence, quantifying the time-resolved vapour fraction of the cavitating bubbly mixtures becomes imperative. We employ the high-speed X-ray densitometry facility at TNO-Ypenburg (The Netherlands) to measure the vapour fraction in the cavitating axisymmetric venturi with a temporal resolution of 1/3600 seconds. The sharp change in density (vapour fraction) across the retracting vapour cavity measured by x-ray densitometry combined with high-frequency dynamic pressure measurements revealed that the condensation shock wave is the only cavity destabilizing mechanism at low σ. The condensation shock wave characteristics such as the propagation velocity, the vapour fraction and the pressure rise across the shock-front as a function of σ are studied. Further, we examine the variation of shock-wave characteristics as it propagates upstream. The vapour fraction fields along with static pressure measurement inside the attached vapour cavity allow us to gain insight into the possible role of compressibility of the bubbly cavitating mixture in cloud cavitation. This further help to explain the dominance of `bubbly shock wave' over 're-entrant jet' as a mechanism driving the periodic cloud shedding in an axisymmetric venturi. |
Sunday, November 20, 2022 6:06PM - 6:19PM |
J09.00008: Interaction of a collapsing bubble with a gas pocket entrapped in solid Changhwan Jang, Jihoo Moon, Ehsan Mahravan, Daegyoum Kim Cavitation bubbles collapsing near boundaries induce high-speed liquid jets due to the asymmetric pressure distribution around the bubbles. The behaviors of the collapsing bubble and liquid jet remarkably differ by the characteristics of the adjacent boundary. Recent studies have revealed that the small gas pockets entrapped on the solid boundary can mitigate the jet momentum and the surface erosion. In this study, we numerically investigate the cavitation bubble collapse near an entrapped gas by varying parameters such as gas compressibility and the volume of the air pocket. In most cases, the liquid jet is directed away from the boundary regardless of the thickness or volume of the gas pocket, indicating notable alleviation of the hydrodynamic loading on the solid surface. Furthermore, the effects of gas compressibility, the distance from the gas pocket to the bubble, and the configuration of the pocket on the bubble-gas pocket interaction are investigated. |
Sunday, November 20, 2022 6:19PM - 6:32PM |
J09.00009: Measurements of Pressure and Nuclei in a Pair of Interacting, Cavitating Vortices Daniel Knister, Harish Ganesh, Steven L Ceccio Incipient cavitation in turbulent shear flows typically first occurs in the weaker stream-wise vortical structures rather than in the stronger span-wise vortices. The weaker (secondary) vortical structures are stretched by the stronger (primary) structures, leading to a transient drop in the core pressures of the weaker vortices. This work studies this phenomenon experimentally by examining the interaction of two initially parallel line vortices experiencing the Crow instability. The tip vortices of a pair of hydrofoils set in a recirculating cavitation channel are used to form this interaction. Inception in the vortices is interrogated with high speed video and acoustic measurements. Pressures and vortex properties are measured in the single phase flow of the vortex interaction using Shake-the-Box particle tracking velocimetry. The nuclei content of the water channel is measured with a Cavitation Susceptibility Meter (CSM). The inception rate observed with acoustic and high speed video measurements is then compared to that predicted by the measured pressure fields and nuclei distributions. |
Sunday, November 20, 2022 6:32PM - 6:45PM |
J09.00010: Development of a 1-D Compressible Wave Model for Predicting the Onset of Cavitation in a Piston Driver Assembly. John Kokkalis, Taj Sobral, Jovan Nedic, Andrew J Higgins The pressure wave dynamics and associated cavitation in a water-filled cylinder are studied experimentally. The use of a double-piston driver and a drop weight facility enables the system loading to be varied between near-constant acceleration and impulsive loading. The pressure in the air-filled volume is varied to enable the onset of cavitation to be induced or suppressed. The piston(s) acceleration is measured via photonic Doppler velocimetry, enabling the loading to be precisely quantified. The resultant wave activity and fluid cavitation are monitored via piezoelectric pressure transducers and direct visualization of liquid interfaces and cavitation onset via high-speed videography. The results are compared to predictions of a one-dimensional compressible wave model. |
Sunday, November 20, 2022 6:45PM - 6:58PM |
J09.00011: How viscous bubbles collapse: topological and symmetry-breaking instabilities in geometrically-nonlinear Stokes flow in 2D Benjamin Davidovitch, Avraham Klein Large floating viscous bubbles whose interior gas is rapidly depressurized exhibit a fascinating instability, whereby radial wrinkles permeate the liquid film in the course of its flattening (Debregeas et al, Science 1998; DaSilviera et al., Science 2000, Oratis et al., Science 2020). We address this instability by studying how Stokes flow in a curve film of a non-inertial incompressible liquid with free surfaces is generated by temporal variation of the curvature. We reveal the experimental observations of Oratis et al. as a universal, curvature-driven surface dynamics, imparted by viscous resistance to temporal variations of the surface's Gaussian curvature, whereby the depressurized bubble flattens by forming a radially moving front that separates a flat core and a spherically-shaped periphery, and becomes wrinkled due to a hoop-compressive stress at the wake of the propagating front. This novel surface dynamics has close ties to ``Jelium physics" in continuum media, where topological defects, akin to charges in electrostatic media, spontaneously emerge to screen elastic stresses. |
Sunday, November 20, 2022 6:58PM - 7:11PM |
J09.00012: Role of Non-condensable Gas in Cavitation Inception Tianyi Hu, Hector Gomez Cavitating flows are ubiquitous in engineering and science applications. While many aspects of cavitation inception for pure fluids are well understood, less is known about cavitation of fluids that contain dissolved non-condensable gas (NCG). We investigate two-component flows, where one of the components is a NCG, and the other component can undergo liquid-vapor phase transformations accompanied by changes in its miscibility with NCG. We propose a continuum model derived from a cubic equation of state and the Navier-Stokes-Korteweg equations. The model is derived from fundamental principles using the Coleman-Noll approach. One of the outcomes of the modeling approach is that the diffusion coefficient of the NCG depends on pressure.. The phase diagram is constructed using isochoric thermodynamics to show that the model can capture the miscibility contrast of NCG in vapor and liquid phase. We plot the critical bubble pressure as function of radius and compare the result against experimental data. Further, we study the dynamic dissolution of a spherical bubble and compare our results with the classical work of Epstein and Plesset. |
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