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 L20: Flow Instability: Complex and Multiphase Flows |
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Chair: Tyler Evans, University of Utah Room: 250 D |
Monday, November 25, 2024 8:00AM - 8:13AM |
L20.00001: Leveraging viscoelastic flow instabilities for remediation of soiled porous media Emily Chen, Sujit S Datta The increased pollution of groundwater aquifers necessitates safe and efficient remediation strategies. One proposed solution involves the injection of viscoelastic fluids into the subsurface environment; however, how exactly viscoelasticity of the displacing fluid may influence soil removal in a 3D, spatially complex environment remains largely unexplored. Here, we investigate flow-induced removal of microplastics from a porous medium by injection of a dilute polymer solution. We use confocal microscopy to directly visualize the pore-scale dynamics of soil removal under imposed fluid flow. Under flow-controlled conditions, we find that the polymer solution flow—above a threshold flow rate—achieves greater removal efficacy than an equivalent flow of a viscous Newtonian solvent. We hypothesize that this results from two mechanisms: (1) additional hydrodynamic forces arising from polymeric elastic stresses, and (2) an elastic flow instability that produces chaotic spatiotemporal flow fluctuations. These in turn collectively enhance soil removal compared to viscous drag-dominated removal for Newtonian flows. Our work thus provides insight into the in situ removal dynamics of microplastics in geometrically-complex environments and highlights the potential for using viscoelastic fluid flows towards remediation of contaminated porous media. |
Monday, November 25, 2024 8:13AM - 8:26AM |
L20.00002: Flow-Induced Structures in Lyotropic Chromonic Liquid Crystals Delace Jia, Qing Zhang, Irmgard Bischofberger Lyotropic chromonic liquid crystals (LCLCs) are materials of interest for their biocompatibility and unique structural properties compared to traditional thermotropic liquid crystals. Their response to shear, however, remains largely unknown. We show that nematic LCLC solutions arrange into intriguing large-scale structures at high flow rates when pushed out of equilibrium by a pressure-driven flow in a microfluidic cell. We align a LCLC solution perpendicular to the flow direction. At low flow rates, the liquid crystal solution remains in this alignment adopting a log-rolling state. At a range of higher flow rates, transient horizontal stripes appear along the flow direction; these stripes subsequently break up into subunits that self-assemble into steady-state vertical band structures. We present scaling arguments for the characteristic length scale of the vertical bands that account for the independence of the selected length scale on flow velocity and for the dependence on the microfluidic cell geometry. We further discuss the director field that underlies the structure of the vertical bands. |
Monday, November 25, 2024 8:26AM - 8:39AM |
L20.00003: Effects of settling thermal inertial particles and bubbles on the hydrodynamic stability of the Rayleigh-Bénard system Saad Raza, Silvia Hirata, Enrico Calzavarini In this study we explore the dynamics of particulate matter on the onset Rayleigh-Bénard (RB) convection. Heavy particles are injected from the top with the cold wall temperature, while light particles are injected from the bottom with the hot wall temperature. For the particulate phase we take into account the viscous (Stokes drag) and inertial hydrodynamics forces (pressure gradient and added mass) on the particles as well as the buoyancy force. Furthermore, the particles are also thermally coupled to the fluid as they have a proper thermal diffusivity and specific heat capacity. The particle properties are parametrized by the added-mass adjusted density-ratio β (which varies in the range [0,3], particle diameter φ, particle injection temperature θ*p, and fluid/particle heat capacity ratio E. The two-fluid model is used to investigate the thermal and mechanical interplay between particles and fluid flow. |
Monday, November 25, 2024 8:39AM - 8:52AM |
L20.00004: The wall-mode elasto-inertia instability of viscoelastic plane Poiseuille flow with porous walls Elmira Taheri, Mohammadreza Mahmoudian, Parisa Mirbod Linear stability analysis (LSA) of pressure-driven channel flow of an Oldroyd-B fluid with porous walls reveals a new elasto-inertial wall mode, absent in impermeable channel with viscoelastic fluids. The presence of porous walls induces Tollmien-Schlichting (TS) instability in Newtonian fluids. We used the modified Darcy-Brinkman-Oldroyd-B model to establish comprehensive equations and boundary conditions. Flow stability is governed by non-dimensional parameters: Reynolds number (Re), Permeability parameter (α), porous thickness ratio (δ), Weissenberg number (Wi), and solvent-to-solution viscosity ratio (β). At low Re numbers (<800), where TS instability occurs due to the large permeability, increasing Wi number initially stabilizes the TS mode. However, with a further increase in Wi (~25), the new elasto-inertial wall mode becomes destabilized. Neutral stability curves show that porous walls decrease the critical Reynolds number (Recr) and destabilize the Oldroyd-B fluid compared to impermeable channels. We also observed the non-monotonic effect of the Wi on flow stability, similar to that in impermeable channels. Notably, increasing the porous layer permeability (low α) shifts the threshold of Wi to lower values. To study the effect of β, we increased it from low values to 1 (the Newtonian case). At high permeability (α=50), for β>0.9, increasing destabilizes the flow and decreases Recr. While in channels with impermeable walls, increasing β stabilizes the flow throughout this range. |
Monday, November 25, 2024 8:52AM - 9:05AM |
L20.00005: Quantitative analysis of double-diffusive instability: Growth and mixing transition of ascending fingers Mohammad Mohaghar, Prathyusha Paresh, Blaire Doss, Ewan Pritchard, Gracen Dutton, Donald R Webster Double-diffusive instabilities (DDI) significantly impact oceanic thermohaline circulation, influencing climate patterns and nutrient distributions. This study employs simultaneous PLIF/PIV measurement techniques to obtain combined, time-evolving density and velocity fields with the aim of exploring several key aspects of DDI. The growth rate of ascending freshwater fingers, the formation of mushroom-shaped structures, and the underlying mixing mechanisms are of specific attention. The experimental setup involves slowly oozing cold fresh water through a perforated tube at the bottom of a tank filled with hot salty water, which facilitates precise control of the density ratio. Flow visualization has revealed the intriguing process of ascending freshwater fingers, their transition into mushroom-shaped structures, and subsequent mixing. These qualitative observations set the stage for detailed quantitative analysis. The primary objective is to determine whether local transitions to turbulence occur at the ends of ascending finger structures. The findings of this study are expected to fill gaps in the existing literature by providing well-designed, quantitative experimental data to study DDI and the associated mixing mechanisms. |
Monday, November 25, 2024 9:05AM - 9:18AM |
L20.00006: Surface Instability of Extremely Soft Solids 'Flowing' Through Confinement Jonghyun Hwang, Mariana Altomare, Howard A Stone A wide range of problems in physics, engineering, and biology involve flows of elastic materials. We studied extrusion-like flows of extremely soft elastic solids (with shear modulus G ~ O(0.1 - 10) Pa) through confinement and identified conditions leading to instability on the extrusion front (gel-air free interface). The observed instability features the formation of spontaneous buckles in the direction transverse to the flow, resulting in a furrow-like morphology that deepens over time. The ‘furrowing’ instability features distinctive characteristics from known elastic surface instabilities and appears to be a new kind of instability. |
Monday, November 25, 2024 9:18AM - 9:31AM |
L20.00007: The influence of elasticity on Faraday instability Igin Benny B Ignatius, Bhagavatula Dinesh, Georg F Dietze, Ranga Narayanan In this work, we investigate the influence of parametric forcing on a viscoelastic fluid layer, considering both gravitationally stable and unstable configurations. In the absence of elasticity, when a viscous layer is vertically oscillated beyond a certain amplitude, large oscillations are observed at the interface due to resonant or Faraday instability. Adding a polymeric gel to this liquid imparts elasticity, affecting the damping rate of momentary disturbances, implying an altering of the threshold and temporal response of Faraday instability. |
Monday, November 25, 2024 9:31AM - 9:44AM |
L20.00008: A Local Dispersion Approach to Gas-Liquid Microfluidic Flow Instability and Droplet Formation Zihao Meng, Carlos H Hidrovo, Sri Harsha Maddila A theoretical model is proposed to describe the instability, regime transition, and predict the droplet generation frequency in gas-liquid droplet microfluidic systems. Gas-liquid microfluidics, unlike traditional liquid-liquid systems, achieve higher throughput and smaller droplets but introduce greater instability, resulting in high dispersion in droplet size and frequency. Therefore, a theoretical model for the instability of high-speed gas-liquid microfluidic systems is essential for better understanding, controlling, and reducing dispersion in these systems. Apparently, the Rayleigh-Plateau and Ganan-Calvo models cannot be adopted due to the presence of confined external flow and co-flow. Furthermore, Gas-liquid systems feature a longer development region in the flow direction, often extending beyond the jet length, making traditional liquid-liquid dispersion relations inapplicable. Consequently, the locality of the dispersion relation must be considered. In light of this, a scaling method was applied to derive a model for jet diameter development in the flow direction. Experimentally obtained boundaries between jetting and dripping regimes were used as data points and fitted to establish the local dispersion relation for gas-liquid systems. Using the theory of open flow instability, this dispersion relation allows for the prediction or experimental validation of characteristics such as regime and frequency. |
Monday, November 25, 2024 9:44AM - 9:57AM |
L20.00009: ABSTRACT WITHDRAWN
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Monday, November 25, 2024 9:57AM - 10:10AM |
L20.00010: Hydrodynamic instability and breakup of a liquid-gas interface via vibration Benjamin Wilfong, Tianyi Chu, Ryan M McMullen, Timothy Koehler, Spencer H. Bryngelson Liquid-gas interfaces break up when subjected to large-amplitude oscillatory accelerations due to hydrodynamic instability. Interface breakup can lead to the injection of the gas phase into the liquid phase below. This gas injection can alter damping properties of fluid-structural systems and depends on the nature of early-stage interface breakup. The breakup that leads to gas injection depends on the configuration details, including the vibration frequency, acceleration amplitude, and character of the initial interface perturbation. We use a 6-equation Baer-Nunziato type diffuse interface model equipped with body force and surface tension effects to simulate early-stage interface breakup and the resulting injection of the gas into the liquid below it. The results indicate a reasonable agreement between simulation growth rates and linear stability analysis, as well as growth-rate independence across random interface perturbations at oscillating accelerations on the order of ten times Earth's gravity with frequencies in the hundreds of hertz. The formation of droplets due to the Rayleigh-Plateau instability in the jetting resulting from the violent acceleration is observed, as well as the entrainment of gas. The volume of ejected droplets and entrained gas are reported over time. |
Monday, November 25, 2024 10:10AM - 10:23AM |
L20.00011: Time-Asymptotic (Floquet) Linear stability of pulsatile particle-laden channel flows Ananthapadmanabhan Ramesh, Konstantinos Tsigklifis, Parisa Mirbod Pulsatile flows have significant applications in microfluidics, including mixing, particle separation, and clog mitigation, as well as in biological systems, such as cardiovascular flows. Linear stability analysis of particle-laden flow with uniform distribution is investigated for a pulsatile flow in a channel. The time- asymptotic (Floquet) stability and modal transient growth during pressure-modulation cycle of pulsatile plane Poiseuille flow is investigated to study the dynamics of the coupled fluid-particle system, where disturbances are decomposed into a product of exponential growth and a sum of harmonics. The coupling between the fluid flow and particles is modeled using Stokes drag, with the particles assumed to be solid, spherical, and heavy. A parametric study of stability in the non-dimensional parameter space, primarily defined by Reynolds number, Womersley number, and the amplitude of the applied pressure modulation, is conducted for different particle relaxation times and mass fractions. Results show that for an S (particle relaxation time) 5x10-5 and f (mass fraction) of 5%, the addition of a pulsating component promotes instability by reducing the critical Reynolds number. Furthermore, it is observed that for S = 5x10-5 and f = 5%, at large frequencies (measured by Womersley number), increasing the amplitude of the oscillating component has a stabilizing effect, while it destabilizes the system at lower frequencies. |
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