交差流れにおける流動不安定性と渦動力学

Burshtein, Noa

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交差流れにおける流動不安定性と渦動力学

https://doi.org/10.15102/1394.00001788

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Item type

学位論文 / Thesis or Dissertation(1)

公開日

2021-03-19

タイトル

交差流れにおける流動不安定性と渦動力学

言語

タイトル

Flow Instabilities and Vortex Dynamics in Intersecting Flows

言語

eng

資源タイプ

資源タイプ識別子

http://purl.org/coar/resource_type/c_db06

資源タイプ

doctoral thesis

ID登録

10.15102/1394.00001788

ID登録タイプ

JaLC

アクセス権

open access

アクセス権URI

http://purl.org/coar/access_right/c_abf2

著者　(英)

Burshtein, Noa

抄録

内容記述タイプ

Other

内容記述

Flow instabilities frequently arise in the proximity of stagnation points, often resulting in the formation of vortices. Predicting vortex formation and dynamics is important for numerous applications including engineering of bridges, airplanes and pipelines. However, vortices are intermittent in nature and it is a challenge to control and study their dynamics. Here we induce vortex formation in 4-way intersections, in which the onset of flow instability is highly sensitive to small changes of the experimental parameters (i.e., channel depth:width ratio α, fluid properties and the Reynolds number, Re). Microfluidic cross-slot geometries, with a novel configuration, are fabricated by selective laser-induced etching in fused silica glass, enabling quantitative flow velocimetry measurements at the cross-section of the intersecting region. By precisely controlling Re, the breaking of symmetry between 4-cells of Dean vortices is initiated at a critical value 10 < Rec < 110, and two co-rotating Dean vortices are induced to merge into a single steady vortex. Subsequent reduction in Re induces a vortex splitting process and the regaining of symmetry. Increasing α results in faster merging dynamics and for α > 0:55 the transition becomes hysteretic. By adjusting α and imposing Re >> Rec, we can control the nature of periodic fluctuations which are governed by the central vortex core structure and the presence of side vortices in the surrounding flow field. Additionally, we find that a slight increase of the elasticity of the fluid, by introducing small quantities of flexible polymers, destabilizes the flow, resulting in symmetry breaking at reduced Rec. We also find that the polymer torque acts counter to the vorticity, reducing the vortex intensity. Our experiments show that by tuning α, Reand elasticity we gain precise control over the intensity, core structure, dynamics and periodic fluctuations of the vortical flow field at the intersection. These experiments capture fundamental processes that govern flow transitions and provide important insights into the mechanisms of symmetry breaking, vortex dynamics and of turbulent drag reduction by polymers. Our findings contribute to the improvement of flow control and advancement of applicable technologies in which vortex suppression is required (i.e., stabilization of structures), or when vortex induced motion is desired (i.e., energy harvesting, mixing enhancement) and are transferable to systems with similar flow behavior (i.e., Taylor-Couette apparatus, T-channels, flows around cylinders and at the wake of airplane wings).

言語

口頭試問日

値

2020-03-24

学位授与年月日

2020-04-30

学位名

Doctor of Philosophy

学位授与番号

甲第51号

学位授与機関

学位授与機関識別子Scheme

kakenhi

学位授与機関識別子

38005

学位授与機関名

Okinawa Institute of Science and Technology Graduate University

著者版フラグ

出版タイプ

VoR

出版タイプResource

http://purl.org/coar/version/c_970fb48d4fbd8a85

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2023-06-26 11:39:32.086092

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交差流れにおける流動不安定性と渦動力学

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