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 T07: Bubbles: Rising and Bursting |
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Chair: Roberto Zenit, Brown University Room: Ballroom G |
Monday, November 25, 2024 4:45PM - 4:58PM |
T07.00001: Viscous drag increases from moisture exchange with an ascending bubble Tom Crouzal, Don R Baker, Reghan J Hill The terminal velocity of a bubble in a viscous fluid, where inertial forces are negligible compared to viscous forces, has been well studied. For interfaces free of surface-active species such as surfactants or contaminants, the ascent velocity is described by the Hadamard-Rybczynski equation; otherwise, it follows the slower Stokes velocity. However, in our observations of bubble dynamics in corn syrup, a common fluid of high viscosity (9 Pa s), bubbles ascend slower than the Stokes equations predict, with the viscous drag coefficient being approximately 23% higher than the Stokes value. To explain this surprising behavior, computations were undertaken to solve the creeping-flow equations for a spherical bubble in a Newtonian fluid with a viscosity that depends on the concentration of a molecular tracer, such as water, subject to advection and diffusion. Numerical simulations investigated various bubble behaviors. The simulations demonstrated that a bubble depletes water in its vicinity, locally increasing the viscosity, which in turn decreases the terminal velocity. Conversely, increasing the water concentration around the bubble decreases the local viscosity, causing the bubble to ascend faster than predicted by the Hadamard-Rybczynski equation. In these two cases, the viscous drag coefficient transitions from a diffusive to an advective regime with increasing Peclet number. At low Péclet numbers, the viscous drag is constant and outside of the range constrained by Hadamard-Rybczynski (2/3) and Stokes (1) values. At high Péclet number, the viscous drag coefficient tends to the range 2/3-1. The Péclet number at this transition is influenced by the specific viscosity-concentration dependence and tracer solubility. These results enhance our understanding of bubble dynamics and coalescence in viscous fluids, crucial for various processes ranging from industrial foaming to volcanic eruptions |
Monday, November 25, 2024 4:58PM - 5:11PM |
T07.00002: Time-resolved three-dimensional measurement of bubble deformation and surrounding water velocity field using 4-D PTV and tomographic reconstruction Jinho Oh, Kyung Chun Kim Bubble dynamics have been studied for several decades, but still many interesting topics remain for more understanding about relationship between bubbles and ambient fluid. Especially, it has rarely reported to experimentally measure flow field with sufficiently large size of deformable bubbles. Here, we introduce an experimental technique to measure 3-D bubble geometry using tomographic reconstruction method and flow field near a deformable bubble using time-resolved three-dimensional particle tracking velocimetry (4-D PTV) with Shake-the-Box (STB) algorithm and vortex-in-cell sharp (VIC#) method. White LEDs and blue LED were utilized to illuminate bubble with deformation and seeding particles respectively. Projected bubble shapes were extracted to original images which were captured by 4 high-speed cameras. Bubble 3-D geometry was reconstructed by the projected bubble shapes and bubble properties like trajectory, rise velocity, equivalent diameter was calculated. The reconstructed bubble mimics bubble's wobbling and trajectory well. Also, bubble rise velocity and equivalent diameter has under 10% error with 2-D image processing results. High rise velocity and entrainment from ambient at bubble wake are observed as bubble rises. Bubble deformation generates various size of vorticities, which cause observation of vortex pairing near deformable bubble. |
Monday, November 25, 2024 5:11PM - 5:24PM |
T07.00003: Alternation of Stress Profile around Bubbles Associated with Velocity Discontinuities Hiroaki Kusuno, Yoshiyuki Tagawa This study focuses on the mechanism of bubble velocity discontinuity (BVD) for a bubble rising in a viscoelastic fluid. Using high-speed polarization measurement, the behavior of the bubble and the surrounding flow structure were observed. The velocity of the rising bubble before and after BVD matched the non-slip and slip conditions, respectively, indicating that BVD is caused by a boundary condition change. This is further supported by the observation that the bubble velocity immediately after its onset matched the slip condition for all bubble volumes. Additionally, particle orientation profiles differed before and after BVD, suggesting variations in polymer relaxation positions. We assumed that the transition from non-slip to slip conditions was due to polymer adsorption and the Marangoni effect. Despite differences in stress components, the consistent rising velocities before and after BVD suggest complex dynamics in viscoelastic fluids, warranting further research. |
Monday, November 25, 2024 5:24PM - 5:37PM |
T07.00004: Numerical Calculation of Viscous Force Balance in Free Bubble Rising in Quiescent Water Pavel Petkov Popov, Xiaofeng Liu This work tackles the problem of numerically resolving the viscous forces in a free air bubble rising in quiescent water. Previous simulations have been able to reproduce the wobbling motion observed in the experimental studies of Moreto et al. (2022). In those simulations, the viscous drag was not captured numerically, due to under-resolution in the boundary layer. A new numerical approach reported here rectifies this, by using three overset curvilinear deforming grids, called the x-, y- and z-grids. The numerical method uses level set phase boundaries, and the governing equations are discretized using a finite-difference approach. The velocity-pressure coupling is solved using the SIMPLE algorithm. Strong flow quantity variations are found near the bubble surface and across the vortex rings shed from the bubble in the wake. To handle the challenges posed by the highly unsteady and thin boundary layer formed on the bubble surface, the three overset grids each place a higher amount of grid cells near the bubble’s surface which is mostly normal to that grid’s direction. Interpolation is performed between the three grids in the regions where the largest component of the surface normal vector changes. Comparison of the experimental data with the numerical simulations is implemented, to offer a reliable way of verification and validation of both results. A resolved simulation of the bubble boundary layer allows us to understand the physics by which the viscous forces are automatically balanced by the pressure force. |
Monday, November 25, 2024 5:37PM - 5:50PM |
T07.00005: Experiments to determine the velocity fields around the skirt bubbles Mithun Ravisankar, Dongyue Wang, Omer Atasi, Dominique Legendre, Roberto Zenit
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Monday, November 25, 2024 5:50PM - 6:03PM |
T07.00006: Inertial droplet dynamics inside a quiescent liquid medium Arahata Senapati, ARNAB ATTA, Rajaram Lakkaraju Inspired by wastewater treatment technologies such as aeration, in this work, we have numerically investigated the dynamics of a collision between a single bubble and a droplet in a quiescent ambient liquid to establish limits required for a successful droplet capture onto a bubble surface (and vice versa). We have varied the bubble diameter to the droplet diameter (∆) in the range of 0.5 to 2 and the droplet Weber number, between 13 to 270, to achieve a head-on collision. An initially accelerated droplet in a viscous liquid can generate a vortex-based liquid jet that can deform the (primary) droplet into a dimpled one or to a toroidal ring with or without a secondary droplet generation. In the case of a bubble-droplet collision, based on the W e d -∆ map, we have identified four regimes, in which (I) the primary droplet attaches to the bubble surface without any secondary droplet generation, (II) instead of the primary one, the generated secondary tiny droplet attaches to the bubble, (III) the droplet deforms into a toroidal ring and attaches to the bubble surface, and (IV) both the droplet and the bubble deform into elongated toroidal rings and a sleeve like attachment takes place. We find the bubble-droplet collisional outcome has a co-existence of regimes I, II and III around Wed ≈ 23 and ∆ = 0.8. The transition from regime III to IV takes place at high Webre numbers, and the boundary separating the mentioned regimes follows W e d inversely proportional to ∆. Via the total energy balance approach, we have constructed a scaling law to describe the transition behaviour from regime III to IV. |
Monday, November 25, 2024 6:03PM - 6:16PM |
T07.00007: Jet size prediction for bursting bubbles with a compound coating Zhengyu Yang, Yang Liu, Bingqiang Ji, Jie Feng The Worthington jet from bursting bubbles can break up into small droplets, transporting chemical and biological contaminants into the atmosphere as aerosols. Although the aerosolization by bubble bursting jet significantly impacts global climate and public health, the influence of the contaminants adsorbed at the bubble surface on the bubble bursting jet remains unclear. Here, we investigate the profound effect of a compound contaminant coating on the jet radius, which deviates from the prediction for jets from bare bubble bursting. We rationalize the deviation of the jet radius by characterizing the excited capillary wave propagation at the air-oil-water interface. We further develop a linearized wave damping model and propose a revised Ohnesorge number with a scaling relation that captures the jet radius reasonably well in a wide range of coating liquid viscosities and thicknesses. Our work not only advances the fundamental understanding for bursting bubbles, but also provides insights to model bursting bubble aerosols in realistic configurations. |
Monday, November 25, 2024 6:16PM - 6:29PM |
T07.00008: Curvature driven acoustics and the physical dynamics of a bubble bursting in a droplet Nilamani Sahoo, Spencer Truman, Andrew Dickerson, Tadd T Truscott We investigate the sounds of bubbles bursting in liquid droplets placed on different wettability surfaces. A high-speed camera is synchronized with an acoustic air microphone and a piezoelectric contact microphone, to capture the physical and acoustic characteristics. The bubble pops, a jet forms, and subsequent capillary waves travel along the droplet toward the contact microphone and back again. Our observations reveal that the peak frequency of the sound recorded by the air microphone during the initial bubble pop, varies with the bubble size irrespective of droplet volume as expected. However, the initial popping amplitude of the signal recorded by the contact microphone is influenced by the droplet shape, which is determined by surface wettability. Superhydrophobic surfaces exhibit a higher frequency magnitude from the emanating jet after bursting compared to hydrophilic surfaces, a result of droplet curvature. The frequency of the induced capillary wave motion is dependent on surface wettability and bubble size for a given droplet volume. In this regard, the spectrogram results can distinguish the frequency pattern of the capillary waves on a hydrophilic versus a superhydrophobic surface. |
Monday, November 25, 2024 6:29PM - 6:42PM |
T07.00009: ABSTRACT WITHDRAWN
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