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 T21: Particle Laden Flows |
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Chair: J. Sebastian Rubio, Johns Hopkins University Room: 250 E |
Monday, November 25, 2024 4:45PM - 4:58PM |
T21.00001: Can surface-attached bubbles serve as effective thermal insulators? Morris R Flynn, S. Amir Shojaee, Zavier Berti Surface-attached air bubbles are known to provide lubricating (i.e., drag reducing) benefits but their contribution to inhibiting heat transfer, whether at the size of lab-on-a-chip devices or at larger scales, is not as well understood. Here, we ask whether surface-attached air bubbles may prove useful as thermal insulators for internal and external flow. In the former case, we apply theory and numerics to study pipe/channel flow and explore scenarios where the bounding surface supplies a uniform surface heat flux (USF) vs. is maintained at a uniform surface temperature (UST). Thus do we identify a remarkable connection between the drag reduction problem and the USF thermal insulation problem, i.e. the proportional change of water temperature with bubble thickness is identical to the proportional change of drag. Also, and although our analysis is conducted in the 'perfect plastron limit', we can, e.g. by evaluating hydrodynamic and thermal slip lengths, contrast our work against related studies where heat transfer occurs through the ridges or pillars that affix the air layer in place. This comparison indicates that the oft-applied adiabatic interface assumption may prove overly restrictive in some regions of the parameter space. |
Monday, November 25, 2024 4:58PM - 5:11PM |
T21.00002: Investigation of Regolith Erosion and Crater Formation during Lunar Landing using an Eulerian-Lagrangian Approach. Aasheesh Bajpai, Ashish Bhateja, Rakesh Kumar The phenomenon of jet-induced cratering in granular beds has garnered significant interest due to its relevance in both natural and industrial settings. Existing literature on crater formation lacks sufficient detail to fully understand the underlying physical processes and develop predictive models for plume impacts. This study aims to enhance existing models and establish mitigation strategies to ensure the safety of future lunar missions by implementing computational simulation capability for the a reliable prediction of surface erosion and crater formation due to plume surface interaction (PSI) during lunar landing. The main objective of this study is to utilize simulations to explore the morphological features of the crater and their temporal evolution. Numerical analysis is performed employing a novel model integrating computational fluid dynamics (CFD) for the gas phase and the discrete element method (DEM) for the solid phase. Utilizing data from Apollo descent recordings, terrain photos, and ascent footage, this research investigates various phenomena such as regolith bed formation, regolith erosion, crater formation and characterization of ejecta properties. The study presents a comprehensive, axisymmetric simulation of plume-induced erosion and crater formation caused by a lunar lander at different plume impingement heights above the lunar surface, in near-vacuum conditions. Sample result, showing flow fields of gas and ejected particles. The study provides insights crucial for lunar landing safety and mission planning. |
Monday, November 25, 2024 5:11PM - 5:24PM |
T21.00003: Continuum Modeling and Numerical Simulation of Active Suspensions Houssem Ben Gozlen, Yongqi Wang, Martin Oberlack Active suspensions consist of self-propelled particles, called active particles, suspended in a fluid. These particles exert an active stress on the fluid. We present a continuum-based model that uses mixture theory to simulate an active suspension. The active particles are assumed to have a uniform orientation in the direction of motion, which is particularly relevant for suspensions of magnetotactic bacteria, where an external magnetic field can control the orientation of the bacteria. The focus of this work is to propose a continuum mechanical model for the partial stress tensor of the particle phase and the interaction forces between the particle and fluid phases, such as drag and lift. The flow of an active suspension in an annular channel of rectangular cross-section is then solved numerically. A stable secondary flow pattern, consisting of a pair of Dean vortices, is formed in the cross-section of the channel. The effect of Reynolds number, channel curvature, and cross-section aspect ratio on the secondary flow is studied. Key physical quantities, including the distribution of the particle volume fraction and the partial velocities of both phases, are also discussed. |
Monday, November 25, 2024 5:24PM - 5:37PM |
T21.00004: Unsettling Behavior: Diffusion's Role in a Sphere Settling Through Sharply Stratified Fluids Dylan D Bruney, Richard M McLaughlin, Roberto Camassa, Claudia Falcon How do particles behave when settling in stratified fluids over extended periods? We delve into the long-term settling dynamics of spheres in such fluids, emphasizing the pivotal role of diffusivity in viscous-dominated regimes. Our study delineates three distinct regimes: Stokes, entrainment, and diffusion. In the Stokes regime, the predominant force results in delayed settling, while the entrainment regime is marked by an added buoyancy force that prolongs residence times at the density transition. Our key finding reveals that diffusivity is a crucial factor causing deviations from the non-diffusive model. Through the use of potassium iodide (KI), a less diffusive salt that aligns well with our model, and sodium chloride (NaCl), a more diffusive salt that exhibits significant discrepancies, we underscore the critical impact of diffusion. Theoretical and experimental comparisons highlight the essential role of diffusivity in understanding prolonged residence times. |
Monday, November 25, 2024 5:37PM - 5:50PM |
T21.00005: Shock-driven Multiphase Instabilities in Expanding Cylindrical Geometry Thierry Daoud, Samuel Briney, Sivaramakrishnan Balachandar, Thomas L Jackson This work examines the particle jetting behavior in a dense bed of particles with 60% volume fraction driven by an air-blast. Three-dimensional Euler-Lagrange simulations were conducted in a cylindrical computational domain using the finite volume code, RocfluMP. The Lagrangian particles are tracked using the particle in cell library PpiclF. The experiments by Rodriguez et al. (2013) are replicated by extending the prior two-dimensional numerical studies to three-dimensions with the aim of capturing the multiphase instabilities that occur both in the gas and granular phases. Recent advances in quasi-steady and added-mass force modeling have enabled state-of-the-art representation of the inter-phase coupling in the simulations. We address accurate computation of force chain networks with the purpose of accurately analyzing the formation of particulate jets. We closely examine the effects of parameter values such as granular material, particle diameter, and shock strength. |
Monday, November 25, 2024 5:50PM - 6:03PM |
T21.00006: Numerical modelling of gas bubbling in active matter Oscar J Punch, Michael W Jordan, Qiang Guo, Christopher M Boyce Granular active matter is an interesting field of research owing to their properties of self propulsion for fluidization. However, the presence of an active matter force, if intrinsically random, could limit the control over the fluidization process. A recent study has shown that dynamically structured patterns of gas bubbles can be produced in granular media by vertically vibrating a bubbling fluidized bed at a resonant frequency, which significantly increases control over the granular matter. Thus, we pose two keys questions: how does bubbling in granular active matter differ from traditional granular matter? And can structured gas bubbling exist in highly active granular matter? We present CFD-DEM simulations of a bubbling fluidized bed with an in-house Gaussian active matter force on the particles and show that the bubbling dynamics are highly dependent on the active matter force. |
Monday, November 25, 2024 6:03PM - 6:16PM |
T21.00007: Scaling Laws of Ejecta Streaks in Lunar Landings J. Sebastian Rubio, Neil S Rodrigues, Matt T Gorman, Miguel X. X Diaz-Lopez, Paul M Danehy, Rui Ni From the crewed Apollo missions of the 1960s to the recent Chang’e uncrewed lunar missions, the interaction between the supersonic exhaust and the lunar surface generates a striking ray system of ejecta particles that travel radially outward at high speeds. While this intriguing pattern has been observed in experiments and simulations, the underlying mechanism remains unclear. These radial ejecta streaks were also observed during an experimental campaign using a Mach 5.3 jet impinging on a granular bed within a large-scale vacuum chamber. Our findings reveal that the radial ejecta streaks are caused by the Gortler instability, which, due to the curvature of the extremely underexpanded jet, induces counter-rotating streamwise vortices within the jet shear layer. These vortices impact the ground and entrain particles in their upwash regions. Experimental measurements from both ground tests and the literature show that the number of streaks strongly depends on the jet diameter at impact and the shear layer thickness, further revealing a power-law scaling with the jet pressure ratio. These insights highlight the pivotal role of fluid dynamics in extraterrestrial landings and provide a foundation for mitigating risks in future planetary missions. |
Monday, November 25, 2024 6:16PM - 6:29PM |
T21.00008: An open-source, four-way coupling, adaptive solver for particle-resolved simulation with hybrid parallelization Xuzhu Li, Chun Li, Xiaokai Li, Wenzhuo Li, Mingze Tang, Zhengping Zhu, Yadong Zeng We present the IAMReX, an adaptive solver for particle-resolved simulation with hybrid MPI and OpenMP parallelization. The fluid equations are solved using a finite-volume scheme on the blocked structured semi-staggered grids with both subcycling and non-subcycling methods.~The interaction between and fluid and particle is resolved using the multidirect forcing immersed boundary method. The associated Lagrangian markers used to resolve fluid-particle interface only exist on the finest-level grid, which greatly helps to save the memory usage. The volume integrals are numerical calculated to accurately capture the free motion of particles, and the repulsive potential model is also included to account for the particle-particle collision. We demonstrate the versatility, accuracy, and efficiency of the present subcycling multilevel framework by simulating fluid-particle interaction problems with various types of kinematic constraints. The source code and testing cases used in this work can be accessed at~\url{https://github.com/ruohai0925/IAMR/tree/development}. All input scripts and raw postprocessing data will be added later. |
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