Effect of Low–Frequency Vibrations on the Hydrodynamic Properties of Single Bubbles at Different Gravity Levels

IF 1.3 4区 工程技术 Q2 ENGINEERING, AEROSPACE
Hao Ni, MingJun Pang
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Abstract

A key aspect of space application technology is the generation and control of multi–phase flows. The efficiency of mass and heat transfer can be significantly improved by adding bubbles or droplets into continuous phases. The effects of the ratio of amplitude to bubble diameter (A/D), Bond number (Bo), and different gravity levels (G/g) on bubble centroid motion and shape oscillation are fully analyzed using the VOF method to understand the bubble–centroid trajectory and shape–oscillation mechanism under low–frequency vibrations. The present studies show that A/D, Bo, and G/g have important effects on bubble trajectory and shape oscillation. There are two types of oscillations for bubble shape: regular oscillation and chaotic oscillation. As Bo and A/D increase, bubble oscillation in a gravity–free environment changes from regular to chaotic oscillation. For the present results, bubble oscillations at different gravity levels (except zero–gravity level) are chaotic oscillations. Three types are recognized for the bubble–centroid motion: levitation, rising and sinking. When both A/D and Bo are tiny, a bubble is hung in its initial position in a gravity–free environment. Bubble–centroid motion changes from sinking to rising with an increase in A/D and Bo. The higher the gravity level is, the shorter the time taken for the bubble to rise is. The change in the flow field seems to be mainly caused by the vibration of fluid particles, almost independent of the level of gravity. The flow field becomes more chaotic as A/D and Bo increase.

Abstract Image

不同重力水平下低频振动对单个气泡水动力特性的影响
空间应用技术的一个关键方面是多相流的产生和控制。在连续相中加入气泡或液滴可以显著提高传质和传热的效率。利用VOF方法,充分分析了振幅与气泡直径之比(A/D)、键数(Bo)和不同重力水平(G/ G)对气泡质心运动和形状振荡的影响,了解了低频振动下气泡质心轨迹和形状振荡机理。研究表明,A/D、Bo和G/ G对气泡轨迹和形状振荡有重要影响。气泡形状的振荡有两种类型:规则振荡和混沌振荡。随着Bo和A/D的增大,无重力环境下的气泡振荡由规则振荡变为混沌振荡。对于目前的结果,在不同重力水平下(除零重力水平外)的气泡振荡都是混沌振荡。气泡质心运动有三种类型:悬浮、上升和下沉。当A/D和Bo都很小时,气泡在无重力环境中悬浮在初始位置。随着A/D和Bo的增加,气泡质心运动由下沉变为上升。重力越高,气泡上升所需的时间越短。流场的变化似乎主要是由流体颗粒的振动引起的,几乎与重力无关。随着A/D和Bo的增加,流场变得更加混乱。
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来源期刊
Microgravity Science and Technology
Microgravity Science and Technology 工程技术-工程:宇航
CiteScore
3.50
自引率
44.40%
发文量
96
期刊介绍: Microgravity Science and Technology – An International Journal for Microgravity and Space Exploration Related Research is a is a peer-reviewed scientific journal concerned with all topics, experimental as well as theoretical, related to research carried out under conditions of altered gravity. Microgravity Science and Technology publishes papers dealing with studies performed on and prepared for platforms that provide real microgravity conditions (such as drop towers, parabolic flights, sounding rockets, reentry capsules and orbiting platforms), and on ground-based facilities aiming to simulate microgravity conditions on earth (such as levitrons, clinostats, random positioning machines, bed rest facilities, and micro-scale or neutral buoyancy facilities) or providing artificial gravity conditions (such as centrifuges). Data from preparatory tests, hardware and instrumentation developments, lessons learnt as well as theoretical gravity-related considerations are welcome. Included science disciplines with gravity-related topics are: − materials science − fluid mechanics − process engineering − physics − chemistry − heat and mass transfer − gravitational biology − radiation biology − exobiology and astrobiology − human physiology
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