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 A21: Bubbly Flows |
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Chair: Elias Balaras, George Washington University Room: 250 E |
Sunday, November 24, 2024 8:00AM - 8:13AM |
A21.00001: Bubble interaction with moderate Re crossflow over a cylinder Andrew Kokubun, Eric William Thacher, Per-Olof Persson, Simo A Makiharju Bluff-body vortex shedding can appear in offshore structures and heat exchangers. It was previously observed that introducing bubbles can modify the shedding frequency. Past studies also demonstrated that shedding frequency is dependent on both bubble size distribution and gas volume fraction (α). To gain insight on how bubbles of various size interact with the carrier phase during shedding, we observed bubble transport initially at ultra-low void fractions of α<0.01% and Reynolds number up to 25,000 using pressure-synchronized tomographic bubble tracking and Stereo PIV experiments supplemented by one-way coupled numerical bubble transport studies utilizing LES-generated velocity fields. This talk focuses on methods utilized in the acquisition as well as the development of appropriate scaling parameters and analysis tools for the interpretation of this rich dataset. |
Sunday, November 24, 2024 8:13AM - 8:26AM |
A21.00002: A phase-resolved force analysis of bubbly flows allows prediction of bubble holdup in the wake of circular cylinders Dohwan Kim, Matthew J Rau The wakes of cylinders in a bubbly cross-flow can induce a non-uniform distribution of void fraction due to the interaction of the bubbles with the wake. This hold up of bubbles can increase flow resistance and promote bubble coalescence, which can reduce the dispersed phase interfacial area and species transport. Here, we investigate the bubble trapping phenomenon by performing velocimetry of a bubbly flow flowing across a 9.5 mm diameter circular cylinder in an upward water channel. Velocimetry of both phases were performed by using tracer particles and shadow image velocimetry in addition to bubble tracking. Cylinder Reynolds numbers ranging from Re = 100 to 3,000 were investigated along with two distinct bubble sizes, 3 mm in diameter and 0.5 mm in diameter, to examine the impact of bubble size on the hydrodynamic forces leading to bubble trapping. A force balance analysis revealed that both the inertia- and lift-to-drag ratios were necessary to predict the bubble clustering dynamics. We captured these effects in an order-of-magnitude analysis to create a bubble trapping parameter, which allows these conditions to be predicted based on the free-stream flow parameters. |
Sunday, November 24, 2024 8:26AM - 8:39AM |
A21.00003: Bubble dynamics in homogeneous shear turbulence Shijie Zhong, Shiyong Tan, Xu Xu, Rui Ni Although homogeneous and isotropic turbulence is the most canonical example of turbulence, it can be rarely found in chemical and biological reactors that have to deal with bubble or oil breakups, in which flows are often generated by impellers with strong and persistent shear. The specific effect of persistent mean shear on bubble breakup remains elusive. In this study, a new experimental facility featuring homogeneous shear turbulence with the mean shear as strong as the local turbulent shear will be introduced. The preliminary results of the bubble morphology throughout the breakup process from this system will be discussed. These experimental results offer valuable insights into the mechanisms underlying bubbly flow and oil emulsion formation in turbulent environments. |
Sunday, November 24, 2024 8:39AM - 8:52AM |
A21.00004: Investigating Taylor Bubble Dynamics in Counter-Current Air-Water Flows: A Combined Numerical and Experimental Analysis Jan Kren, Iztok Tiselj, Blaž Mikuž In pressurised water reactor (PWR), understanding two-phase flows is critical during events like boiling heat transfer and Loss of Coolant Accident (LOCA). During these scenarios, the slug flow regime, characterized by elongated Taylor bubbles, occurs in steam generators, challenging system stability. This study investigates Taylor bubbles in counter-current air-water flows using high-fidelity numerical simulations and advanced experiments. We examined two flow regimes: transitional (Re = 1400) and fully turbulent (Re = 5600), focusing on bubbles under stagnant conditions where buoyancy is balanced with the downward flow's inertial drag. Experimentally, we analyzed bubble disintegration, interface dynamics, and liquid phase velocity using Particle Image Velocimetry. High-speed video and image analysis revealed asymmetries in Taylor bubbles, deviating from the expected axisymmetric profiles. Disturbance waves on the bubble interface with amplitudes ranging from 10 to 100 micrometers were tracked. Numerically, we simulated bubble behavior and disintegration mechanisms, employing Volume-Of-Fluid (VOF) approach with geometric interface reconstruction and high-order Runge-Kutta time schemes. We focused on the transitional flow regime and notably observed the formation of a secondary vortex in the turbulent wake at finer mesh resolutions. To counter bubble breakup in turbulent regime we propose new grid-scale surface tension model. |
Sunday, November 24, 2024 8:52AM - 9:05AM |
A21.00005: Transport of gas bubbles by vortex rings Zhixuan Liu, Zhixuan Liu, Stuart B Dalziel, Daria Frank Multiphase vortex rings are commonly observed in environmental and industrial settings. Interactions between vortex rings and bubbles allow bubbles to be entrained and accumulate in the vortex core and subsequently transported over a distance. Our study aims to investigate the behaviours of gas bubbles that are fed into vortex rings at different stages. |
Sunday, November 24, 2024 9:05AM - 9:18AM |
A21.00006: Density ratio effects on turbulent bubbly upflow in a vertical channel: similarities and differences Min Lu, Peng Chen, Xiang Yang, Zixuan Yang In this study, we investigate the effects of density ratio on turbulent bubbly upflow in a vertical channel. High-resolution numerical simulations were conducted using a coupled level-set and volume-of-fluid method to accurately capture the liquid-gas interface. Various cases were analyzed to examine flow morphology and turbulence statistics. Results indicate that increasing the density ratio from 10 to 30 leads to increased drag and a reduction in mean momentum. However, further increases in the density ratio to 1000 do not significantly alter bubble morphology, turbulence statistics, or drag. An analysis of the Reynolds stress transport equation reveals that the insignificant differences in drag at high density ratios (> 30 ) are caused by the reduced wall-normal gradient of the streamwise velocity above large bubbles, resulting in less production. Additionally, we introduce new inner layer transformation and outer layer scaling to re-establish the law of the wall (LoW) and the defect law for the mean velocity profiles in bubbly flows. The results show that the transformed velocity profiles collapse to the LoW much better than the original velocity profiles and that the Zagarola-Smits scaling successfully recovers the defect law for the outer layer of the mean velocity profiles. |
Sunday, November 24, 2024 9:18AM - 9:31AM |
A21.00007: Entrainment characteristics of a swirling plunging jet Toshan Lal Sahu, Prasanta Kumar Das, RAJARAM LAKKARAJU
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Sunday, November 24, 2024 9:31AM - 9:44AM |
A21.00008: Multiphase Flow Measurements with Superhydrophobic Surfaces in Constrained Geometries Angel Francisco Rodriguez, Sean Oser
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Sunday, November 24, 2024 9:44AM - 9:57AM |
A21.00009: Probing Flow Condensation with Acoustic Signatures Ying Sun, Dylan Wallen, Lida Yan, Ahmed Allam, Kishan Shivashankar Bellur, Hari Pandey, Stephen Pierson, Han Hu Two-phase thermal management systems, with both boiling and condensation processes, offer great potential and heat transfer coefficients that are orders of magnitude higher than traditional single-phase systems. However, two-phase flows can suffer from a wide range of interfacial instabilities leading to significant thermal performance degradation. In this study, we aim to characterize dominating physical mechanisms of flow condensation, such as turbulent diffusion in annular liquid film and interfacial waves, using an integrated system of acoustic and optical sensing techniques and thermofluidic characterizations. A wideband acoustic emissions sensor and high-sensitivity accelerometer are utilized to capture acoustic and vibrational signatures that signal the onset of liquid film formation and interfacial waves during flow pattern transitions. Compared to optical imaging, wideband acoustic emission sensing allows for higher sampling rates to capture high-frequency interface oscillations critical to the flow regime transitions and works well even for condensation in opaque tubes. Acoustic features are correlated with thermofluidic processes. By relating thermal performance metrics with these dynamic signatures in acoustic regimes, we explore the ability to probe and monitor critical flow regime transitions and transport efficiency in flow condensation. |
Sunday, November 24, 2024 9:57AM - 10:10AM |
A21.00010: Data-driven analysis of bubble fragmentation in turbulence Andre Calado, Elias Balaras Bubble deformation and fragmentation in turbulent flows are critical phenomena in many industrial processes and natural systems, leading to a mass-transfer cascade. Despite extensive research, some aspects of the underlying physics remain poorly understood. The bubble Weber number plays a crucial role in determining different regimes of bubble behavior, including small deformation (without breakup), oscillatory breakup, and sudden breakup. |
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