Fluid Dynamics
New submissions
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New submissions for Fri, 10 May 24
- [1] arXiv:2405.05494 [pdf, other]
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Title: Localization and bistability of bioconvection in a doubly periodic domainComments: 10 pages, 9 figuresSubjects: Fluid Dynamics (physics.flu-dyn); Soft Condensed Matter (cond-mat.soft); Biological Physics (physics.bio-ph)
A suspension of swimming microorganisms often generates a large-scale convective pattern known as bioconvection. In contrast to the thermal Rayleigh-Benard system, recent experimental studies report an emergence of steady localized convection patterns and bistability near the onset of instability in bioconvection systems. In this study, to understand the underlying mechanisms and identify the roles of particle self-propulsion in pattern formation, we theoretically and numerically investigate a model bioconvection system in a two-dimensional periodic boundary domain. In doing so, we extend a standard bioconvection model by introducing the equilibrium density profile as an independent parameter, for which the particle self-propulsion is treated as an independent dimensional parameter. Since the large-scale vertical structure dominates in this system, we are able to simplify the model by truncating the higher vertical modes. With this truncated model, we analytically derived the neutrally stable curve and found that the particle motility stabilizes the system. We then numerically analyzed the bifurcation diagram and found the bistable structure at the onset of instability. These findings, localization and bistability, are consistent with experimental observations. We further examined the global structure of the bistable dynamical system and found that the non-trivial unstable steady solution behaves as an edge state that separates the basins of attractors. These results highlight the importance of particle self-propulsion in bioconvection, and more generally our methodology based on the dynamical systems theory is useful in understanding complex flow patterns in nature.
- [2] arXiv:2405.05539 [pdf, other]
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Title: Instability of a dusty shear flowComments: 37 pages, 13 figuresSubjects: Fluid Dynamics (physics.flu-dyn)
We study the instability of a dusty simple shear flow where the dust particles are distributed non-uniformly. A simple shear flow is modally stable to infinitesimal perturbations. Also, a band of particles remains unaffected in the absence of any background flow. However, we demonstrate that the combined scenario -- comprising a simple shear flow with a localised band of particles -- can exhibit destabilisation due to their two-way interaction. The instability originates solely from the momentum feedback from the particle phase to the fluid phase. Eulerian-Lagrangian simulations are employed to illustrate the existence of this instability. Furthermore, the results are compared with a linear stability analysis of the system using an Eulerian-Eulerian model. Our findings indicate that the instability has an inviscid origin and is characterised by a critical wavelength below which it is not persistent. We have observed that increasing particle inertia dampens the unstable modes, whereas the strength of the instability increases with the strength of the coupling between the fluid and particle phases.
- [3] arXiv:2405.05682 [pdf, other]
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Title: Mapping dissolved carbon in space and time: An experimental technique for the measurement of pH and total carbon concentration in density driven convection of CO$_2$ dissolved in waterComments: Supplementary Material containing videos of spatiotemporal pH and carbon concentration can be found in Zenodo via the link: this https URLSubjects: Fluid Dynamics (physics.flu-dyn)
We present an experimental technique for determining the pH and the total carbon concentration when \ch{CO2} diffuses and flows in water. The technique employs three different pH indicators, which, when combined with an image analysis technique, provides a dynamic range in pH from 4.0 to 9.5. In contrast to usual techniques in which a single pH indicator is used, the methodology presented allows not only to produce a binary classification (pH larger or smaller than a given threshold) but to access a much more complete continuous spatial distribution of pH and concentration levels in the system. We calibrate the method against benchmark solutions and further demonstrate its potential by measuring the pH and total carbon concentration in a density driven convection (DDC) of carbon-enriched water. The motivation for testing the method in this particular experiment comes from the fact that DDC plays a pivotal role in the efficiency of engineered carbon storage processes. The application of the technique presented here provided a direct window for the analysis of the spatial distribution of captured carbon in the DDC flow.
Cross-lists for Fri, 10 May 24
- [4] arXiv:2405.05640 (cross-list from cs.DC) [pdf, other]
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Title: Experience and Analysis of Scalable High-Fidelity Computational Fluid Dynamics on Modular Supercomputing ArchitecturesAuthors: Martin Karp, Estela Suarez, Jan H. Meinke, Måns I. Andersson, Philipp Schlatter, Stefano Markidis, Niclas JanssonComments: 13 pages, 5 figures, 3 tables, preprintSubjects: Distributed, Parallel, and Cluster Computing (cs.DC); Mathematical Software (cs.MS); Fluid Dynamics (physics.flu-dyn)
The never-ending computational demand from simulations of turbulence makes computational fluid dynamics (CFD) a prime application use case for current and future exascale systems. High-order finite element methods, such as the spectral element method, have been gaining traction as they offer high performance on both multicore CPUs and modern GPU-based accelerators. In this work, we assess how high-fidelity CFD using the spectral element method can exploit the modular supercomputing architecture at scale through domain partitioning, where the computational domain is split between a Booster module powered by GPUs and a Cluster module with conventional CPU nodes. We investigate several different flow cases and computer systems based on the modular supercomputing architecture (MSA). We observe that for our simulations, the communication overhead and load balancing issues incurred by incorporating different computing architectures are seldom worthwhile, especially when I/O is also considered, but when the simulation at hand requires more than the combined global memory on the GPUs, utilizing additional CPUs to increase the available memory can be fruitful. We support our results with a simple performance model to assess when running across modules might be beneficial. As MSA is becoming more widespread and efforts to increase system utilization are growing more important our results give insight into when and how a monolithic application can utilize and spread out to more than one module and obtain a faster time to solution.
Replacements for Fri, 10 May 24
- [5] arXiv:2404.08412 (replaced) [pdf, other]
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Title: PiRD: Physics-informed Residual Diffusion for Flow Field ReconstructionComments: 22 pagesSubjects: Fluid Dynamics (physics.flu-dyn); Artificial Intelligence (cs.AI)
- [6] arXiv:2404.09034 (replaced) [pdf, other]
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Title: Using Biot-Savart boundary conditions for unbounded external flow on Eulerian meshesSubjects: Fluid Dynamics (physics.flu-dyn)
- [7] arXiv:2404.15117 (replaced) [pdf, other]
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Title: Momentum deficit and wake-added turbulence kinetic energy budgets in the stratified atmospheric boundary layerComments: 42 pages, 22 figures, 1 tableSubjects: Fluid Dynamics (physics.flu-dyn)
- [8] arXiv:2405.04276 (replaced) [pdf, other]
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Title: Alfvén waves at low Magnetic Reynolds numberComments: 36 pages, 18 figuresSubjects: Fluid Dynamics (physics.flu-dyn)
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