Using braids to quantify interface growth and coherence in a rotor-oscillator flow
Name
PhysRevFluids.5.054504.pdf
Description
Published version
Size
2.86 MB
Format
Adobe PDF
Checksum (MD5)
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Author(s)
Filippi, Margaux
Budišić, Marko
Allshouse, Michael R.
Atis, Séverine
Peacock, Thomas
Date Issued
May 2020
Journal
Physical Review Fluids
Publisher
American Physical Society (APS)
Citation
Filippi, Margaux et al. "Using braids to quantify interface growth and coherence in a rotor-oscillator flow." Physical Review Fluids 5, 5 (May 2020): 054504 © 2020 American Physical Society
Version
Final published version
Abstract
The growth rate of material interfaces is an important proxy for mixing and reaction rates in fluid dynamics and can also be used to identify regions of coherence. Estimating such growth rates can be difficult, since they depend on detailed properties of the velocity field, such as its derivatives, that are hard to measure directly. When an experiment gives only sparse trajectory data, it is natural to encode planar trajectories as mathematical braids, which are topological objects that contain information on the mixing characteristics of the flow, in particular through their action on topological loops. We test such braid methods on an experimental system, the rotor-oscillator flow, which is well described by a theoretical model. We conduct a series of laboratory experiments to collect particle tracking and particle image velocimetry data, and we use the particle tracks to identify regions of coherence within the flow that match the results obtained from the model velocity field. We then use the data to estimate growth rates of material interface, using both the braid approach and numerical simulations. The interface growth rates follow similar qualitative trends in both the experiment and model, but have significant quantitative differences, suggesting that the two are not as similar as first seems. Our results shows that there are challenges in using the braid approach to analyze data, in particular the need for long trajectories, but that these are not insurmountable.
MIT Department
Massachusetts Institute of Technology. Department of Mechanical Engineering
Woods Hole Oceanographic Institution
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DOI of Published Version
https://doi.org/10.1103/physrevfluids.5.054504
