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 U20: Bubbly Flow Physics III |
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Chair: Angeliki Laskari, TU Delft Room: 206 |
Tuesday, November 22, 2022 8:00AM - 8:13AM |
U20.00001: Scale-out of small channel two-phase flow contactors Haoyu Wang, Duan Cong, Panagiota Angeli In process engineering, flows in small channels are characterized by increased specific interfacial area and improved mass transfer rates. The two-phase flow patterns significantly influence the performance of fluidic devices. While many studies have studied flow pattern in single channels, there is still a lack of general guidelines on how to replicate the performance of a single unit to multiple ones for scale-up while avoiding fluid maldistribution and flow fluctuations among channels. We report a double manifold system for the scale up of two-phase liquid processes in small channels, based on a resistance network model. The manifold consists of 5 parallel single channels with total flow rates of both phases ranging from 0.2 to 50 mL/min. The flow patterns and distribution in the manifold channels were investigated for a hexane water-system. Under the conditions used, plug flow is expected in the single channels. In the double manifold system, it was found that in each of the parallel single channels plug flow also established, while the flow distribution was uniform for different flow rates. An infrared LED sensor was developed to monitor the flow distribution and measure plug length in the manifold channels. |
Tuesday, November 22, 2022 8:13AM - 8:26AM |
U20.00002: Pseudo elastoinertial turbulence in viscoelastic fluids Mithun Ravisankar, Roberto Zenit Turbulence induced by the bubbly swarms (pseudo turbulence) has been extensively studied due to its relevance in industrial applications. Despite the prevalence of non-Newtonian fluids in many of these applications, most studies focused on the Newtonian continuous phase. We investigate the homogeneous bubble swarm rising at a moderate Reynolds number in a viscoelastic shear-thinning fluid by varying the gas volume fraction. The liquid velocity fluctuations were measured in the wake behind the bubble swarm using particle image velocimetry (PIV). We observe a significant change from the classical energy spectral decay with the wave number, $k^{-3}$, by gradually increasing the Weissenberg number. Further, experiments were conducted in a shear thinning inelastic fluid to quantify the effects of elasticity. The work provides insights into the emerging research of elastoinertial turbulence (EIT) recently observed in viscoelastic fluids. |
Tuesday, November 22, 2022 8:26AM - 8:39AM |
U20.00003: Pair dispersion of bubbles in turbulence Shiyong Tan, Rui Ni Pair dispersion is a classical tool to understand the mixing and transport of pollutants by turbulent flows. For light bubbles, the dispersion dynamics deviate from the tracer limit and provide a new way of understanding their coalescence and transport. One of the challenges for tracking a pair of bubbles with a very small initial separation experimentally is associated with triangulating bubbles and tracking them in a dense cloud. We approached the problem by leveraging our new bubble tracking method, which utilizes a novel feature correlation method combined with our open-sourced Shake-the-Box code. This method allows us to track pairs of bubbles very close to each other and enables us to obtain sufficient statistics to study bubble pair dispersion in homogeneous and isotropic turbulence. The results clearly show not only the ballistic and superdiffusive scaling but also a new transition scaling, which possibly implies the mutual trapping of the pairs in the turbulent vortices. |
Tuesday, November 22, 2022 8:39AM - 8:52AM |
U20.00004: Vortex Shedding in a Dispersed Multiphase Flow Eric W Thacher, Andrew Kokubun, Per-Olof Persson, 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, the nonlinear shift in shedding frequency with bubble size has not been explained. Through experimental and numerical study of size-dependent bubble transport, we describe the mechanism causing this change in shedding frequency. The motion of monodisperse bubbles (range of 40-400 microns) introduced upstream of a cylinder is studied in 3D using tomographic bubble tracking; the flow field at the centerline plane is determined simultaneously with 2D-3C stereo PIV. The experimental results are used to validate a one-way coupled point-particle tracking model, for which the flow field is computed using high-order LES. The model is used to produce statistics on the size-dependent bubble motion in the wake of the cylinder. These statistics provide insight into the mechanism for frequency shift, which will be confirmed in higher phase fraction flows that are no longer one-way coupled. |
Tuesday, November 22, 2022 8:52AM - 9:05AM |
U20.00005: Turbulence modulation by deformable bubbles Xu Xu, Shiyong Tan, Ashik Ullah Mohammad Masuk, Ashwanth Salibindla, Rui Ni The unique feature of multiphase flows is that the dispersed phase not only reacts to the background turbulence but also modulates and sometimes drives turbulence. In particular, a rising swarm of bubbles in an otherwise quiescent medium can actively induce turbulence, but little is known how bubbles modulate pre-existing turbulence, particularly an intense one. Intense turbulence can deform bubbles through random slip velocity and the surrounding strain. Part of the energy is left in the small-scale eddies in the wake of the bubbles, and another part is stored in the enlarged interfacial energy, which is later returned to the flow via bubble relaxation. The goal of this study is to understand this relative contribution by different mechanisms and how bubbles bypass energy cascade by pumping energy directly from large scales to small scales. Experimentally, we track dense tracers around many deforming bubbles and average the results based on the bubble orientation and the slip velocity direction. The results will shed some new light on turbulence modulation by deformable bubbles and energy cascade in turbulent multiphase flows. |
Tuesday, November 22, 2022 9:05AM - 9:18AM |
U20.00006: Bubble-chain flows rising in a two-dimensional slit channel Jieun Yeo, Hyungmin Park We experimentally investigate the bubble-chain flow in a slit (two-dimensional) channel, focusing on the bubble dynamics and resulting bubble-induced liquid flow, while varying the bubble generation frequency up to 21Hz. Using two-phase particle image velocimetry, the flow statistics of liquid and gas phases are measured simultaneously and analyzed to explain mechanism underlying the interactions between two phases. As the bubble generation frequency increases, a series of bubble-bubble interaction pattern occur such as two-bubble pairing, clustering, and merging, and we found that horizontal/vertical distance between bubbles and the wake structure of leading bubbles is associated with such changes. In addition, we show that the interaction between bubbles causes a significant change in the liquid flow in the viewpoint of time-averaged (entrainment) and fluctuating (turbulence) components both in vertical and horizontal directions. In particular, we will discuss the characteristic frequency scales that are associated with the region where such bubble-bubble interaction pattern is dominant. |
Tuesday, November 22, 2022 9:18AM - 9:31AM |
U20.00007: Evolution of Gas Volume Fraction in the Wake of 2-D and 3-D Ventilated Supercavities Prachet Jain, Nicholas A Lucido, Harish Ganesh, Steven L Ceccio Vehicles submerged in water experience significant friction drag, degrading performance. |
Tuesday, November 22, 2022 9:31AM - 9:44AM |
U20.00008: Experimental study on the ventilated two-dimensional supercavity beneath a moving flat plate near the free surface in a still fluid Jeonghyeon Nam, Yeunwoo Cho A flat plate moves with a constant speed near the free surface in a still fluid. Beneath the moving plate and near the leading edge, a rectangular cavitator is perpendicularly attached and compressed air is injected behind the cavitator. Resultant cavity-flow patterns are observed according to the speed of the moving plate (0.5 to 2 m/s) and the volume flow rate of the compressed air (20 to 100 liter/min). When the speed of the plate is relatively small (0.5m/s and 1m/s), the plate bottom is partially covered by a two-dimensional supercavity; at 0.5 m/s, for all flow rates, the cavity length is time-periodically changed and a thin air film is generated behind the cavity wake and, at 1m/s, as the air flow rate increases, the length of a steady cavity increases and bubble-shedding occurs at the cavity wake. When the speed of the plate is relatively high (1.5m/s and 2m/s), the plate bottom is fully covered by a two-dimensional supercavity; for specific air flow rates, the length of a steady cavity becomes larger than the plate length and, beyond the trailing edge of the plate, reaches the free surface with a re-entrant jet closure. |
Tuesday, November 22, 2022 9:44AM - 9:57AM |
U20.00009: Turbulent boundary layers over gas-liquid interfaces Angeliki Laskari, Lina Nikolaidou, Christian Poelma Skin friction drag reduction methods via air injection have become an area of significant innovation for the shipping industry in recent years. Apart from specific technical considerations for optimal performance and net energy savings, the associated flow geometry provides a very challenging fundamental problem in multiphase turbulent flows. In the present work, we analyse this problem in a laboratory setting using snapshot and time-resolved Particle Image Velocimetry and high-speed photography measurements. In particular, the effects of variable air injection under a flat plate on the incoming liquid turbulent boundary layer (TBL) upstream of the injection location (Reτ = 3300) are statistically evaluated at a wall-parallel plane in the log region (y = 0.1δ). This includes steady or unsteady blockage effects on the incoming liquid flow due to the formation of air bubbles, wall-attached air patches and air layers downstream of the injection location. In addition, the correlation of spanwise-meandering velocity structures of the upstream liquid TBL (at the same wall-parallel plane) with the temporal evolution and coalescence of the injected air patches, is also analysed through simultaneous time-resolved measurements of both the upstream liquid and the downstream gas phases. |
Tuesday, November 22, 2022 9:57AM - 10:10AM Author not Attending |
U20.00010: No surface tension needed for stable phase interfaces and droplets Nelson Longmire, Steven Showalter, Daniel T Banuti Droplets, bubbles, and their phase interfaces are often thought to imply the presence of surface tension. Analysis of droplet formation at Diesel conditions, i.e. at pressures exceeding the critical pressure of the injected fuel, exclusively focuses on mixing effects that may cause the formation of surface tension. Here, we introduce a physical mechanism that causes stable interfaces without any surface tension: thermal gradient induced interfaces (TGIIF) are based on distributions of density and thermal conductivity, and can occur at high subcritical and arbitrary supercritical pressures. TGIIF cause the formation of droplets even in pure supercritical fluids, in absence of phase equilibrium and surface tension. As if surface tension was acting, a diffuse droplet of a pure cool transcritical fluid in a hot environment stabilizes, and its interfacial density gradient sharpens rather than diffuses; a droplet with elliptical cross-section regresses towards a circular cross section. The existence of TGIIF thus challenges our concept of droplets and the interpretation of experimental data: the observation of a circular droplet shadowgraph does not necessarily imply the presence of phase equilibrium and surface tension, but could show a TGIIF. |
Tuesday, November 22, 2022 10:10AM - 10:23AM |
U20.00011: Periodically Structured Coalescence of Bubbles in a Vertical Stream Rising Through Dense Suspensions Boyuan Chen, Azin Padash, Wasif Zia, Alireza Bordbar, Javad Omidi, Christopher M Boyce Bubble rise in dense suspensions exhibits unusual behaviors due to the highly non-Newtonian rheology. We report the periodically structured coalescence of succeeding bubbles in a bubble stream in corn starch-water and glass bead-soybean oil dense suspensions. The coalescence behavior is examined and characterized systematically over a wide range of packing fractions and bubble injection conditions in a pseudo-2d system through video analysis. We further employed magnetic resonance imaging (MRI) to characterize similar coalescence behaviors under different conditions in a fully 3D system. The periodically structured coalescence is attributed to the leading bubbles decelerating in the shear-thickening regime, while the trailing bubbles accelerate in the shear-thinning regime, leading to coalesce. |
Tuesday, November 22, 2022 10:23AM - 10:36AM |
U20.00012: Kolmogorov turbulence co-exists with pseudo-turbulence in buoyancy-driven bubbly flows Vikash Pandey, Dhrubaditya Mitra, Prasad Perlekar Bubble laden flow appears in a variety of natural and industrial processes. A suspension of such bubbles at moderate volume fractions generates complex spatiotemporal flow patterns also known as pseudo-turbulence or bubble-induced agitation. We investigate the spectral properties of buoyancy-driven bubbly flows. We identify the relevant energy transfer mechanisms using high-resolution numerical simulations and phenomenology of homogeneous turbulence. At a high enough Galilei number (ratio of the buoyancy to viscous forces), the kinetic energy spectrum shows the Kolmogorov scaling with a power-law exponent -5/3 for the range of scales between the bubble diameter and the dissipation scale. For scales smaller than the dissipation range, the physics of pseudo-turbulence is recovered. |
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