Vortex Dynamics, Breakdown, and Stability in Moderate Reynolds Number Microfluidics

Yu, Xinyi

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Overview

Year:: 2021
Contributor:: Yu, Xinyi (creator); Ault, Jesse (Advisor); Brown University. Engineering: Fluid, Thermal, and Chemical Processes (sponsor)
Genre:: theses
Subject:: Microfluidics; Fluid mechanics
Extent:: vi, 35 p.

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Description

Abstract:: The lid-driven cavity flow is among the most studied fluids problems, in which a horizontally moving lid drives the flow within a cavity. Here, we consider a modified shear-driven cavity flow based on the research of J. R. Torcyznski, who identified features resembling vortex breakdown and some more modified cavity flow. A range of simulations are performed using OpenFOAM for different geometries and Reynolds numbers. Due to time constraints, only some experiments related to the cavity channels were carried out using microfluidics techniques and visualized with a microscope. The flow in the cavity is characterized by the transition of two dominant vortex breakdown regions in the upper and lower half of the channel, respectively. For the standard cavity geometry with the length, width and depth all equal, as the Reynolds number increases, a swirling region formed in the center of the cavity gradually develops into a bubble-type vortex breakdown region that appears, and ultimately the two regions grow and merge into one, located at the center of the cavity. Varying the geometry also affects the topological structure of the vortex breakdown regions. For cavity widths between 1 and 3 channel depths, the structure is the same as described above. When the width reaches and exceeds 5 channel depths, the bubble type vortex breakdown regions form near the top and bottom of the cavities. At these widths, the bubbles grow with Reynolds number but do not appear to merge. However, the symmetry of the vortex breakdown which we observed in every simulation was not observed in the experiments, and the structures of vortex breakdown in the experiments all demonstrate some small differences from the numerical results. Related vortex breakdown dynamics were investigated in other geometries, although these were not investigated in as much detail. For example, simulations were performed in channel bends of 90 degrees for a variety of outlet widths, but these were not pursued in the same level of detail as the cases in the cavity channel. This study provides numerical and experimental evidence of the complex structures and transition processes of vortex breakdown regions in shear-driven cavity flows as a function of Reynolds number and geometry.
Notes:: Thesis (Sc. M.)--Brown University, 2021

Content

Citation

Yu, Xinyi, "Vortex Dynamics, Breakdown, and Stability in Moderate Reynolds Number Microfluidics" (2021). Fluid, Thermal, and Chemical Processes Theses and Dissertations. Brown Digital Repository. Brown University Library. https://repository.library.brown.edu/studio/item/bdr:by2t3jqu/

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Fluid, Thermal, and Chemical Processes Theses and Dissertations

Theses and Dissertations for the Fluid, Thermal, and Chemical Processes department.
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