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 L21: Multiphase Flow Modeling and Theory |
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Chair: Mario Trujillo, University of Wisconsin - Madison Room: 250 E |
Monday, November 25, 2024 8:00AM - 8:13AM |
L21.00001: Quantifying a Common Inconsistency in RANS-VoFModeling of Water and Oil Core Annular Flow Mario F Trujillo, Hirthick Nagarajan Current trends in modeling CAF of oil and water combine the interface capturing methodology of VoF with the computational savings of a RANS approach. As demonstrated mathematically, this results in an inconsistency in the overall RANS-VoF treatment and incurs a number of omissions in the solution of oil fraction advection and momentum. To quantify these inconsistencies, five CAF cases with increasing water-based Reynolds number, Rew, are considered and solved via DNS. Symptoms of the inconsistencies include a lack of diffusivity in the average local oil fraction and qualitative errors in the prediction of the flow behavior in the entrance and fully-developed regions, as well as in the transition between these two regions. With the absence of diffusivity in mean oil fraction, knowledge about mean interface distribution is lost as well. From a momentum perspective, the more troubling issue is the absence of fluctuating terms associated with viscous and surface tension forces. For momentum advection, terms associated with fluctuating density can be safely ignored due to the similar magnitude between oil and water density. |
Monday, November 25, 2024 8:13AM - 8:26AM |
L21.00002: Dynamics of inertial particles in quiescent flow under microgravity. Jeremie Auzoux, Facundo Cabrera-Booman, Karl Cardin, Cheng Wang, Nicolas Plihon, Mickael Bourgoin, Raúl Bayoán B Cal We investigate experimentally the deceleration of heavy spherical particles initially settling at their terminal velocity in quiescent water when gravity is abruptly suppressed. The experiment is mounted in the Dryden Drop Tower located in Portland State University which provides a step gravity reduction from g to 10-2 g in 20 milliseconds. Several particle-to-fluid density ratios and several particle diameters (i.e. particle Galileo numbers) are explored. When the gravity is suppressed, particles slow down until their velocity vanishes. We analyse this transient relaxation at the light of the celebrated Maxey-Riley-Gatignol (MRG) equation, systematically quantifying the relative importance of the different hydrodynamic forces at play (drag, added mass, buoyancy and history forces). |
Monday, November 25, 2024 8:26AM - 8:39AM |
L21.00003: A novel mass-conserving contact line boundary condition for conservative second-order phase-field models Reed Lin Brown, Shahab Mirjalili, Makrand A Khanwale, Baskar Ganapathysubramanian, Ali Mani The phase-field method is a widely adopted technique for simulating multiphase flows. One popular class consists of models based on second-order phase-field equations, which offer advantages over higher-order equations in certain aspects, including better bound preservation and milder timestep restrictions. However, an ongoing challenge with such models is the treatment of contact lines. Because a second-order phase-field equation admits only one constraint on the phase-field variable at each boundary, it is unclear how to simultaneously conserve mass and model contact line physics. In this presentation, we describe a novel solution to this problem: a local mass conservation (no-flux) boundary condition on the phase-field equation in conjunction with a slip velocity boundary condition on the momentum equation. The result is a second-order phase-field model that conserves mass while also accurately modeling contact lines in systems with arbitrary equilibrium contact angles. We describe the formulation of the model as applied to the Conservative Diffuse Interface (CDI) model and present numerical results of canonical contact line test cases. |
Monday, November 25, 2024 8:39AM - 8:52AM |
L21.00004: On the singular limit of three-phase contact lines in a ternary Cahn-Hilliard model Eric W Hester We investigate the physically relevant singular limit of a thermodynamically-consistent model of ternary liquid-liquid phase separation. The emergence of three-phase contact lines significantly complicates the analysis. We combine three techniques to purse this analysis to arbitrary asymptotic order: 1. Physically meaningful and geometrically elegant coordinate systems adapted to each subproblem. 2. A comprehensive symbolic algebra system for performing and validating the analysis. 3. Little-known identities for complete analytic solutions to the codimension-1 spectral subproblem. We also discuss the algorithms needed for accurate numerical validation of these models, and explore the applications of these simplified models to microfluidic manufacture of Janus droplets. |
Monday, November 25, 2024 8:52AM - 9:05AM |
L21.00005: A diffuse-interface formulation for melting and vaporization of plastics Danny Long, Aritra Mukherjee, Salar Salimi, Lucy J Brown, Henry Collis, Shahab Mirjalili, Suhas Jain, Luca Brandt, Corinna Schulze-Netzer Thermo-chemical recycling of plastics, which uses heat and oxidizer-reduced atmospheres to convert waste into syngas, is an emerging technology for recycling multi-polymer materials. |
Monday, November 25, 2024 9:05AM - 9:18AM |
L21.00006: Investigation into the impact of interface thickness and Phase-Field modeling on interfacial instabilities in compressible multiphase flow William Joseph White, Ziyang Huang, Eric Johnsen Excessive and non-uniform numerical diffusion poses challenges for accurate simulations of compressible interfacial flows with shocks using diffuse interface methods. Even with high-order accurate methods, material interfaces continually diffuse, thus making material regions ambiguous and deleteriously impacting wave propagation across interfaces. Further, the presence or absence of interfacial instabilities in canonical test problems appear to be highly dependent on initial conditions and schemes, with results varying substantially between methods for problems like the Kelvin-Helmholtz instability. In this work, we investigate the impact of interface thickness on interfacial instabilities and the interface topology for several flows, including the Kelvin-Helmholtz and Richtmyer-Meshkov instabilities, and a shock-bubble and shock-droplet interaction. Through the use of consistent and conservative Phase Fields, we are able to separate the modeling and numerical errors by maintaining uniform and constant thickness interfaces. We simulate several systems when the interface is free to diffuse and deform and when it is controlled by the Phase Field to observe the impact of interfacial thickness on the flow, and to observe the differences between the models with and without the Phase Field. |
Monday, November 25, 2024 9:18AM - 9:31AM |
L21.00007: Physics-informed sub-grid scale modeling of break-up of VOF simulations Zonghao Zou, Olivier Desjardins Accurately predicting droplet size distributions in liquid atomization processes is crucial for many fields such as drug manufacturing, fuel combustion, and metal powder production. Standard Eulerian interface capturing methods such as Volume-of-Fluid (VOF) face challenges with numerical break-up of thin interfacial structures, since the smallest resolvable interfacial scale is controlled by the mesh size. Mesh-induced break-up prevents spray atomization simulations from reliably predicting droplet size distributions. Recently, the Reconstruction with 2 Planes (R2P) method has introduced the novel ability to represent and transport sub-grid scale films with arbitrarily small thicknesses without numerical break-up. In this work, we integrate R2P with a consistent volume-filtered framework for modeling the dynanics of sub-grid scale films. We propose a simple hole nucleation model based on a minimum film thickness criterion. Once a hole is formed, film retraction due to high-curvature rims is modeled using a Taylor–-Culick flow model. Finally, the resulting ligaments are identified and broken up using a model based on Rayleigh-Plateau instabilities. We test each sub-model in simple test cases, then deploy the full framework to simulate the aerobreak-up of a droplet. Finally, we explore application of this approach to more complex and realistic break-up scenarios. |
Monday, November 25, 2024 9:31AM - 9:44AM |
L21.00008: A Near Field Lagrangian Dispersion Model for Sprays Michael Mason, Mario F Trujillo Typically, RANS-based Lagrangian-Eulerian (LE) models of spray atomization are performed with the near-field region unresolved. As a result, physics, including radial dispersion, is not well captured. A new Near-field Lagrangian Dispersion Model (NFLDM) is presented to improve stochastic radial liquid dispersion. This Langevin-based model employs self-similar representations of mean velocity and Reynolds stress fields obtained from experimentally validated Volume of Fluid (VoF) simulations. Additionally, the model employs an autocorrelation function for computational time-step independence. A generalized model of the self-similarity is developed using VoF data from a range of spray simulations employing 2-4.5 MPa ambient pressure, a range of injection velocities, injections of n-dodecane and methanol, and multiple nozzles. The NFLDM is first compared against LE model results representative of typical industry simulations by using temporally-averaged Projected Mass Density (PMD) measurement, and the NFLDM is found to yield significant improvement over the standard LE. Then, the NFLDM is assessed over a wider range of conditions, yielding satisfactory PMD agreement with the VoF for the majority of the simulations. |
Monday, November 25, 2024 9:44AM - 9:57AM |
L21.00009: An heuristic model for droplet phase change in supersonic flows Lorenzo Angelilli, Venkatramanan Raman Traditional liquid carbon-based fuels possess low heat capacity and latent heat of evaporation, enabling rapid heating and evaporation. In conditions where compression work and heat transfer are dominant, such as in supersonic flows, the external layer of the droplet can quickly reach a critical state and be advected away, significantly accelerating the phase transition beyond the traditional thermal/diffusive process. This study presents a heuristic model designed to predict droplet phase change in supersonic flows, addressing the intricate interaction between high-speed gas dynamics and liquid phase transformations. The model integrates fundamental principles from thermodynamics and trans-critical states to estimate evaporation rates and droplet size evolution in supersonic environments. By simplifying the complex physics involved, the model provides a practical approach for understanding droplet behavior under extreme aerodynamic conditions. Key features of the model include considerations of shockwave-induced pressure and temperature variations, droplet deformation, and the effects of the trans-critical state. Validation against experimental data and computational fluid dynamics simulations demonstrates that the heuristic model accurately captures the essential trends in droplet evaporation time scales, offering valuable insights for integration with Eulerian-Lagrangian CFD simulations. |
Monday, November 25, 2024 9:57AM - 10:10AM |
L21.00010: The reflection of a shock pulse at a liquid-gas interface Nikolaos Bempedelis, Tom A Smith We present an analytical method for computing the reflection and transmission of a non-linear pulse of finite width, i.e. an impulsive shock wave, at a liquid-gas interface. The problem is treated analytically by considering idealised pulses and solving a series of consecutive Riemann problems. In the acoustic limit, the method produces identical results to linear acoustic theory, where reflection and transmission coefficients depend only on the impedance difference. However, the characteristics of the reflected and transmitted waves depart from linear theory as the pulse strength increases. It is shown that the reflection problem cannot only consider the interface, and wave interactions between the incident pulse and reflected waves must also be considered. For a water-air interface, we explain how a reflecting pulse can put the water into tension without any incident negative pressure. It is further shown that the magnitude of the reflection coefficient decreases with increasing incident shock pressure, and the reflected pulse widens. Reflections of pulses with positive and negative pressures temporarily create negative pressure regions with greater magnitude than the incident pulse. Finally, the method is used to predict the reflection of non-idealised waves. Comparisons with numerical simulations show that the reflection characteristics can be qualitatively explained using the analytical method, and the reflection coefficients are accurately predicted. |
Monday, November 25, 2024 10:10AM - 10:23AM |
L21.00011: Investigation of different Phase-Field models in compressible multiphase flows under a unified high-order and bound-preserving framework Ziyang Huang, Shahab Mirjalili, Makrand A Khanwale, Suhas Jain, Eric Johnsen Godunov-type schemes have been widely used in compressible multiphase flows to capture both shocks and material interfaces. One of the long-lasting challenges is that material interfaces are thickened and will eventually disappear due to numerical diffusion with the use of Godunov-type schemes. Phase-field models have shown their effectiveness in competing with numerical diffusion adjacent to material interfaces, leading to a constant interface thickness. The reduction-consistent formulation provides a high-order accurate and bound-preserving framework that is general enough for coupling different phase-field models for compressible multiphase flows. Under this framework, the behavior of different phase-field models in compressible multiphase flow regime is investigated, and the interaction between the Godunov-type schemes and phase-field models are studied. This allows for accurate interpretation of numerical simulation results of different phase-field models, particularly their subgrid behavior, for compressible multiphase flows. |
Monday, November 25, 2024 10:23AM - 10:36AM |
L21.00012: Investigation of particle collision statistics in varying dimensionality configurations in multiphase shocktube simulations Bradford A Durant, Frederick Ouellet, Rahul Babu Koneru Simulation of multi-phase compressible flows are of great interest since they can help predict events such as solid-rocket boosters and volcanos. Such events require performing 3D simulations with particles as they can resolve the most of the flow physics. However, even for non-fully resolved point-particle simulations, 3D simulations can be computationally expensive. Any potential reduction in computational costs would be welcomed, however this requires accurate models to account for the loss of resolution. It was observed, when simulating a particle bed in a shocktube experiment, that the particle front position predictions noticeably improved with experimental data as the simulation increased dimensionality. These simulations modelled collisions using the Harris-Crighton model and used point-particle drag models. This work focuses on repeating the previous simulation but with the use of a resolved soft-sphere collision model to analyse particle-particle interactions in the flow. Investigation of the collision metrics and statistics on its contribution to the dimensionality effect will be explored. The shocktube experiment will be simulated using a finite-volume Euler-Lagrange hydrocode. Aspects of dimensionality such as particle seeding locations, and collisional vectors are varied in 2D and 3D over a range of simulations. By simulating these different configurations, the effects on dimension-based modelling constraints on particle collisions of the particle fronts can be studied. |
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