Bulletin of the American Physical Society
76th Annual Meeting of the Division of Fluid Dynamics
Sunday–Tuesday, November 19–21, 2023; Washington, DC
Session R41: Bubbly Flows II |
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Chair: jonathan cheng Room: 206 |
Monday, November 20, 2023 1:50PM - 2:03PM |
R41.00001: Numerical detection of bubble creation and extinction events under a breaking wave using Optimal Network algorithm Saswata Basak, Umberto C. Bitencourt, Qiang Gao, Grant B Deane, M. Dale Stokes, Lian Shen Bubbles generated by breaking waves play a crucial role in coupling oceans with the atmosphere by enhancing gas transfer, heat exchange, and sea spray aerosol formation. In this study, we perform direct numerical simulations of wave breaking wherein the topology of the air-water interface is captured by a coupled level-set and volume-of-fluid method. We develop an Optimal Network (ON) algorithm, which is a parallel, Lagrangian bubble tracking algorithm that utilizes information on bubble position, shape, velocity, and volume to establish a network of non-conflicting maps quantified by pseudo-distance error norms, between lists of bubbles belonging to adjacent time instants. The ON algorithm is capable of categorizing events involving bubbles, aerated cavities, and filaments into continuity, fragmentation, coalescence, entrainment, and bursting at the sea surface. We apply suitable filters and dynamic task scheduling to reduce the computational complexity of detecting non-binary fragmentation and coalescence. By employing the ON algorithm as a post-processing tool, we obtain bubble trajectories and residence times, construct bubble history graphs, and detect all bubble creation and extinction events that span the spatio-temporal evolution of bubble plumes beneath breaking waves. |
Monday, November 20, 2023 2:03PM - 2:16PM |
R41.00002: Measurements and modelling of the hydrodynamical and acoustical properties of planar bubble curtains Simon Beelen, Dominik Krug The noise emission during pile driving during the construction of offshore installations such as wind farms is harmful to sea life and needs to be mitigated. The usage of bubble curtains is a proven and widely employed solution for this purpose. However, open questions remain e.g. with regard to the relevant noise reduction mechanisms and the reliability of predictions of the system. To tackle these, we developed a novel measurement system for the bubble properties along with acoustical measurements. Our approach is based on electrical, contact-based needle sensors in combination with an optical system. The system is employed to study planar bubble plumes evolving from different nozzle types. All cases display consistent self-similar behavior with spreading rates increasing with increasing gas flow rate, but also varying for different nozzle configurations. We show that such variations critically affect the outcome of available hydrodynamical models for planar bubble plumes. Moreover, we propose a hydrodynamical model which describes our data well and which can be used to predict plume properties in practice. Coupling these results to existing acoustical models, our data allows us to critically assess bubble curtain performance. |
Monday, November 20, 2023 2:16PM - 2:29PM |
R41.00003: Experimental investigation on the morphology of bubble curtains Daeun Lee, Hyungmin Park Among various geometries of bubbly flows, the bubble curtains forming a barrier with a large number of bubbles are attracting increasing attention as an eco-friendly method (strategy) to confine or guide the floating/submerged pollutants, such as the plastic particles, oil, and wastes in river and sea. In the present study, the laboratory-scale bubble curtains are experimentally investigated in water tunnel (with and without the freestream) with varying air flow rates. The morphological features of the bubble curtain are measured using the high-speed shadowgraphy (optical flow) and particle image velocimetry (PIV). They are used as a basis to draw some analytical modeling using the control volume analysis to explain the transition in the bubble-curtain shape. With a horizontal freestream (up to 0.3 m/s), we examine how the characteristics of the gas phase within the bubble curtain are modified by the crossflow. We will also report the liquid-phase flow entrained and/or guided by the bubble curtain under each condition. |
Monday, November 20, 2023 2:29PM - 2:42PM |
R41.00004: Time-dependent hydrodynamics of bubble columns Martin Obligado, Sandra Orvalho, Mark Terentyak, Anthony Davelman, Marek Ruzicka, Alain Cartellier Bubble column reactors, where gas is injected at the bottom of an initially stagnant liquid, are widely used in chemical engineering. They often operate in the heterogeneous regime combining thus high gas concentrations (15 to 40%) and strong velocity fluctuations (25-30% times the mean). Furthermore, processes are usually dynamic as the injected gas flowrate may be unsteady, they can suffer sudden change of operating parameters, etc… Owing to such flow complexity, no reliable scaling rules are available for reactor designers, and scale-up from the lab units to industrial units still relies on empirical formulæ. |
Monday, November 20, 2023 2:42PM - 2:55PM |
R41.00005: Bubble Induced Flow Topology Changes in Cross Flow over a Cylinder Eric W Thacher, Bruno Van Ruymbeke, Celine Gabillet, Simo A Makiharju Vortex-induced vibration from cross flow over bluff bodies is an important design consideration in devices from flow meters to nuclear reactors. While past researchers have shown that introducing bubbles to the flow can decrease vibration amplitude while increasing shedding frequency (up to a void fraction of 10%), the parameter space spanned by bubble size, Reynolds number, and void fraction has only been partially explored. We explore Reynolds numbers from 100,000 to 360,000 at void fractions from 0 to 0.04%. The injected bubbles range from 0.2 to 1 mm in size, with a volumetric mean diameter of roughly 0.3 mm. POD and SPOD analysis is used to identify structures and dominant frequencies present in the multiphase flow, which are compared to PIV measurements of the single-phase velocity field. In contrast to previous literature which predominantly indicates a shedding frequency increase, we find a non-monotonic shift in the shedding frequency when varying the void fraction and Reynolds number. The shedding frequency is decreased for the subcritical regime, and there are indications that a premature shift to the drag crisis can be induced for certain parameter ranges. Changes to the eddy length and recirculation length are also presented. |
Monday, November 20, 2023 2:55PM - 3:08PM |
R41.00006: The passive scalar spectrum in turbulent bubble suspensions Niklas Hidman, Henrik Ström, Srdjan Sasic, Gaetano Sardina When bubbles rise in a liquid, due to buoyancy, they induce liquid velocity fluctuations, referred to as bubble-induced turbulence or pseudo-turbulence. These liquid fluctuations differ from the single-phase turbulent fluctuations. The turbulent kinetic energy spectrum scales with a different exponent (-3) compared to the classic Kolmogorov -5/3-spectrum of single-phase isotropic turbulence. However, while the velocity spectrum behavior has been deeply analyzed in the last years with experiments and numerical simulations, we still do not know how bubbles influence the spectrum of a passive scalar. In this work, we assess the statistics of passive scalars in bubble suspensions using fully-resolved Direct Numerical Simulations (DNS). The governing parameters are similar to heat transport in air-water systems with 2.5 mm bubbles at volume fractions of 2-5 %. From the DNS, we identify key mixing mechanisms and observe a double scaling of the scalar spectrum with a -3 power law at the scales below the bubble diameter and a classic -5/3 scaling at larger scales. We also compute the scalar spectral budget and show how the balance of the net transfer and the diffusive dissipation induces the −3 scaling at small scales (where the production is negligible). |
Monday, November 20, 2023 3:08PM - 3:21PM |
R41.00007: Bubble motion in moderate Re crossflow over a cylinder Andrew Kokubun, Eric W Thacher, Simo A Makiharju Vortex shedding in bluff-body flows appears in offshore structures and heat exchangers. Previous studies have shown that with the introduction of bubbles into the carrier liquid, the shedding frequency increases monotonically with respect to void fraction up to a gas volume fraction, α, of 10%. To gain insight on how bubbles interact with the shedding flow, we start with nominally one-way coupled experiments at α<0.01%, and will later expand to α=O(1%). For our low void fraction experiments, a single highly monodisperse stream of bubbles is injected upstream of a 25 mm circular cylinder in crossflows with Reynolds number up to 25,000. The bubble diameter is varied between experiments, as bubble size has been observed to modify the shedding frequency at higher void fractions. High-speed cameras are used to track 3D bubble trajectories, and simultaneous Stereo PIV and dynamic pressure transducer measurements are used to relate the bubble trajectories to the shedding phase and flow field. |
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