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 A08: Bubbles: General |
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Chair: Xiaofeng Liu, San Diego State University Room: 136 |
Sunday, November 20, 2022 8:00AM - 8:13AM |
A08.00001: Non-intrusive Measurement of the Pressure Field over a Free Rising Bubble in Quiescent Water Xiaofeng Liu, Jose R Moreto, Jesus Figueroa, Bradley J Zelenka The instantaneous pressure field surrounding an air bubble free rising in quiescent water has been successfully measured by using time-resolved planar Particle Image Velocimetry at Reynolds number of 1840, Weber number of 6.48 and Eotvos number of 8.5. The pressure reconstruction was performed using the parallel ray omni-directional integration method. Time-resolved consecutive images with image size of 1K x 1K pixels were acquired at 1000 frames per second using a Photron FastCam SA-Z camera. Analysis shows that the viscous term contributes no more than 1% to the reconstructed hydrodynamic pressure, while the hydrostatic pressure presents a dominant share of the final entire hydro pressure at a magnitude of about 60 times of that of the hydrodynamic part for this bubble rising flow. The ascending motion of the bubble generated vorticity, and vortex rings were shed off the bubble surface. The pressure measurement result was verified by comparing the buoyancy force calculated using the Archimedes' Principle with that obtained through the numerical integration of the reconstructed hydro pressure on the bubble outer surface. Excellent agreement was also achieved by comparing the drag coefficient calculated from the force balance with that calculated using an empirical formula. |
Sunday, November 20, 2022 8:13AM - 8:26AM Author not Attending |
A08.00002: On the Dynamics of Hydrogen Bubbles at Pt Microelectrodes Aleksandr Bashkatov, Syed Sahil Hossain, Alexander Babich, Hannes Rox, Xuegeng Yang, Gerd Mutschke, Kerstin Eckert The growth of single hydrogen bubbles at Pt microelectrodes is studied during water electrolysis performed in an acidic electrolyte over a wide range of concentrations and cathodic potentials. New bubble growth regimes have been identified and summarized in the regime map. The regimes differ in terms of whether the bubble evolution proceeds with a monotonic or oscillatory variation of the electric current and if and how a carpet of microbubbles underneath the bubble evolves. Key features such as the growth law of the bubble radius, the dynamics of the microbubble carpet, the onset time of the oscillations, and the oscillation frequencies have been characterized as a function of the concentration and electric potential. Based on the analysis of the forces involved including electric and hydrodynamic (induced by Marangoni convection) forces, a sound hypothesis is formulated regarding the mechanism of the bubble oscillations and the evolution of a micro-bubble carpet. |
Sunday, November 20, 2022 8:26AM - 8:39AM |
A08.00003: A Hele-Shaw Newton's cradle: The motion of bubbles in Hele-Shaw cells Daniel J Booth, Ian M Griffiths, Peter D Howell We present a model for the motion of approximately circular bubbles in a Hele-Shaw cell. The bubble velocity is determined by a balance between the hydrodynamic pressures from the external flow and the drag due to the thin films above and below the bubble. We find that the qualitative behaviour depends on a dimensionless parameter $\delta \propto \mathrm{Ca}^{1/3}R/h$, where $\mathrm{Ca}$ is the capillary number, $R$ is the bubble radius and $h$ is the cell height. An isolated bubble travels faster than the external fluid if $\delta>1$ or slower if $\delta<1$, and the theoretical dependence of the bubble velocity on $\delta$ is found to agree well with experimental observations. Furthermore, we show how the effects of interaction with cell boundaries and/or other bubbles also depend on the value of $\delta$. For example, in a train of three identical bubbles travelling along the centre line, the middle bubble either catches up with the one in front (if $\delta >1$) or is caught by the one behind (if $\delta <1$), forming what we term a Hele-Shaw Newton's cradle. |
Sunday, November 20, 2022 8:39AM - 8:52AM |
A08.00004: Dynamics of a rising bubble impacting on the inclined wall with different angle and wettability Jinyong CHOI, Hyungmin Park In this study, we experimentally investigated the dynamics of a rising bubble (Reynolds numbers in the order of 102-103) impacting on the inclined wall, installed on top of the static water tank. While varying the material of the wall (e.g., PMMA and glass) and the inclination angle from 5° to 85°, we measured the bubble trajectory and shape deformation with high-speed photography and the liquid flow field with the two-phase particle image velocimetry. It is measured that the bubble either slides along the wall or perform repeated bouncing while rising, of which the transition is associated with both the inclination angle and wall boundary condition (i.e., wettability). By analyzing the bubble trajectory (such as the period and amplitude of the rebounds), and the spatio-temporal evolution of the flow field around the impacting bubble and the wall, we will further discuss the mechanism of the transition in the bubble dynamics. |
Sunday, November 20, 2022 8:52AM - 9:05AM |
A08.00005: A model for the interaction of an oil droplet and a gas bubble rising in a quiescent liquid Madeline E Federle, Roberto Zenit Gas flotation for oily-water mixtures is common practice in many industrial cleanup applications. Gas bubbles (typically air) come into contact with dispersed oil drops, leading to compound drops (gas-filled oil drops) that rise faster. Although this process is widely used in the industry, the details of the interaction and the capture conditions are not well understood. Experiments were conducted considering different bubble and droplet sizes, as well as changing the viscosity of the surrounding liquid. The experiments demonstrated, that in most cases, the air bubble and oil drop did not coalesce but rather bounced off one another, resulting in a velocity jump of the oil droplet. A mathematical model was developed using these observations. A force balance of buoyancy, weight, drag, added mass, and a history force was used to predict the interaction process prior to and after the collision. The model presented offers new insight into both the application of droplet-bubble interactions as well as exploring bubble wake and fluid relaxation effects on an oil droplet. |
Sunday, November 20, 2022 9:05AM - 9:18AM |
A08.00006: Unsteady Flow Field Simulation of a Single Bubble Rising in Quiescent Water Jesus Figueroa, Pavel P Popov, Xiaofeng Liu The dynamic behavior of a single air bubble rising in quiescent water is investigated numerically at Reynolds number of 1840, Weber number of 6.48 and Eotvos number of 8.5. Both theoretical (Clift, et al. 1978) and experimental (Moreto et al. 2022) studies indicate that the bubble with the aforementioned non-dimensional number values exhibits a wobbling motion during the ascending process. By simulating the instantaneous 3-D flow field around the single rising bubble, the mechanism resulting in the wobbling motion, especially the lateral oscillation of the bubble, is elucidated. The numerical method uses level set phase boundaries immersed in a spatially structured grid. The governing equations are discretized using a finite-volume approach. The velocity-pressure coupling is solved using the SIMPLE algorithm. Strong flow quantity variations can be 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 nature of the bubble rising flow, close comparison of the numerical simulation results with the experimental data obtained with Time-Resolved Particle Imaging Velocimetry is implemented, to offer a reliable way of verification and validation of the results. |
Sunday, November 20, 2022 9:18AM - 9:31AM |
A08.00007: Control-based methods to unravel complexity for propagating Hele-Shaw bubbles. Joao Fontana, Alice B Thompson Feedback control (FBC) can be used to force a system into a particular configuration, and also to help explore its nonlinear behaviour, including direct observation of unstable states. Importantly, Control-Based Continuation (CBC) can be performed directly in experiments, with no need for a mathematical model. We discuss how FBC and CBC can be implemented for the propagation of bubbles within a Hele-Shaw channel. Here the depth-averaged Darcy model predicts an infinite sequence of steadily-propagating solutions, one which is linearly stable. It is not clear to what extent the predicted unstable states persist into the real 3D system. We develop a system of FBC for the propagating bubble, with feedback delivered via fluid injection at the sides of the channel at amplitudes determined from real-time observation of the bubble shape. We use the model to design a suitable control gain and overcome the complexities of controlling a propagating bubble moving past a fixed array of actuators. For CBC, the target state is unknown a priori, but detected so that the control amplitudes are zero at steady state (non-invasive control). We explore the effect of noise and delay in this system, with particular reference to our experiments in progress for a deformable but stationary bubble. |
Sunday, November 20, 2022 9:31AM - 9:44AM Author not Attending |
A08.00008: Motion reversals of rising electrogenerated hydrogen bubble Alexander Babich, Aleksandr Bashkatov, Kerstin Eckert, Xuegeng Yang, Sahil Hossain, Gerd Mutschke The growth of hydrogen bubbles in water electrolysis is of high practical relevance due to the prominent role of hydrogen in the future energy system. The dynamics even of a single bubble is already multifaceted and was recently found to be associated with Marangoni convection[1, 2], bubble-microlayer interaction [3, 4], and electric forcing [4]. |
Sunday, November 20, 2022 9:44AM - 9:57AM |
A08.00009: Effect of wall inclination on the near wall rising behaviour of air bubbles in still water Raghav Mundhra, Rajaram Lakkaraju, Prasanta K Das Path instability of rising bubbles is a well-established phenomenon. We conducted experiments using high speed photography to analyze the dynamics of buoyant air bubbles(3-4 mm) rising near an inclined wall(50-120° with horizontal) in still water. The flow properties were computed using image processing. As previously observed, the bubble shows a bouncing trajectory with constant amplitude and frequency, when the wall was placed vertically. As the wall inclination angle was reduced, the amplitude of the bounces decreased. After a critical angle, the bouncing motion transitioned into a sliding motion in which the bubble steadily rises under the wall. There have been no reported studies on the motion of a bubble rising along an obtusely inclined wall. For such conditions, we found that upto a critical inclination angle, the bubble bounces on the wall once and then it rises upwards. On increasing the angle beyond this critical value, the bubble rises straight upward with negligible wall effect. Thus, the bubble motion can be divided into four different regimes depending on the wall inclination – sliding (0-54°), bouncing (54-90°), one bounce and rise away (90-114°) and straight rising (114-180°). For air bubbles in water, the transition angles are 54° and 114°. |
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