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Collisions among elongated settling particles: The twofold role of turbulence
KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics. KTH, Centres, SeRC - Swedish e-Science Research Centre. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics. KTH, Centres, SeRC - Swedish e-Science Research Centre. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. Department of Physics, Indian Institute of Technology Palakkad, Palakkad 678 557, India.ORCID iD: 0000-0003-0130-6258
Department of Mechanical and Maritime Sciences, Chalmers University of Technology, 412 96 Gothenburg, Sweden.
KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, Centres, SeRC - Swedish e-Science Research Centre. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics. Department of Energy and Process Engineering, Norwegian University of Science and Technology (NTNU), Trondheim, Norway.ORCID iD: 0000-0002-4346-4732
2024 (English)In: Physics of fluids, ISSN 1070-6631, E-ISSN 1089-7666, Vol. 36, no 1, article id 013319Article in journal (Refereed) Published
Abstract [en]

We study the collision rates of settling spheres and elongated spheroids in homogeneous, isotropic turbulence by means of direct numerical simulations aiming to understand microscale-particle encounters in oceans and lakes. We explore a range of aspect ratios and sizes relevant to the dynamics of plankton and microplastics in water environments. The results presented here confirm that collision rates between elongated particles in a quiescent fluid are more frequent than those among spherical particles in turbulence due to oblique settling. We also demonstrate that turbulence generally enhances collisions among elongated particles as compared to those expected for a random distribution of the same particles settling in a quiescent fluid, although we also find a decrease in collision rates in turbulence for particles of the highest density and moderate aspect ratios ( A = 5 ) . The increase in the collision rate due to turbulence is found to quickly decrease with aspect ratio, reach a minimum for aspect ratios approximately equal to 5, and then slowly increase again, with an increase up to 50% for the largest aspect ratios investigated. This non-monotonic trend is explained as the result of two competing effects: the increase in the surface area with aspect ratio (beneficial to increase encounter rates) and the alignment of nearby prolate particles in turbulence (reducing the probability of collision). Turbulence mixing is, therefore, partially balanced by rod alignment at high particle aspect ratios.

Place, publisher, year, edition, pages
AIP Publishing , 2024. Vol. 36, no 1, article id 013319
National Category
Meteorology and Atmospheric Sciences
Identifiers
URN: urn:nbn:se:kth:diva-342840DOI: 10.1063/5.0177893ISI: 001146263000013Scopus ID: 2-s2.0-85182727118OAI: oai:DiVA.org:kth-342840DiVA, id: diva2:1833363
Note

QC 20240201

Available from: 2024-01-31 Created: 2024-01-31 Last updated: 2024-02-12Bibliographically approved

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Grujić, AnđelaBhatnagar, AkshayBrandt, Luca

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