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A Study on Flow and Turbulent Structure around Bubbles in Bubbly Flow

气泡流中气泡周围的流动和湍流结构研究

基本信息

批准号：
11450072
负责人：
ARITOMI Masanori
金额：
$ 8.32万
依托单位：
Tokyo Institute of Technology
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
1999
资助国家：
日本
起止时间：
1999 至 2001
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-11450072/
关键词：
Fluid Mechanics Bubbly Flow Flow Structure around Bubble Doppler Effect of Ultrasound Multi-point Void Fraction Method Flow Visualization UVP WMT 多点ボイド率計測装置乱流粒子-流体モデル画像処理超音波パルスのドップラー効果

项目摘要

In order to clarity the microscopic flow structure around bubble on turbulent two phase flow, UVP was applied to the measurement of counter-current and co-current bubbly flows. By treating experimental data statistically, liquid velocity profile around bubbles were investigated. The following results were obtained :(1) The flow field around bubbles can be separated into three regions ; a boundary layer, a main flow region, and a transition region.(2) Velocity gradient is independent of gas flow rate conditions near bubble.(3) The flow structure surrounding a bubble can be well characterized by the bubble Reynolds number.(4) When a bubble is influenced by the wake of the leading bubbles, the flow is highly agitated by the vortex shed from the leading bubbles. When a bubble rises up in liquid without the influence of the leading bubbles, the flow in the bubble boundary layer remains laminar.A new electrode-mesh device has been applied to studies on bubble flow. Extensive data processing methods have been developed that offers the possibility to evaluate the local instantaneous void fraction, bubble rising velocity and bubble volume as well as their time and cross-sectional averaged values. These averages were used to conclude on the local distribution of the superficial gas velocity. The following results were obtained :(1) The proposed algorithms have been applied to bubble flow in a rectangular channel (<UG> = 0-5 mm/s , <UW> = 0-25 mm/s and two air injection configuration). Accuracy in the prediction of void fraction was found within 5 % by comparison with VIP supplied data.(2) The reconstructed volume flow showed uncertainties in the order of up to 20 % for true gas velocities lower 300 mm/s and up to 30 % above.

为了研究两相湍流中气泡周围的微观流动结构，将紫外线偏振（UVP）技术应用于逆流和并流泡状流的测量。通过对实验数据的统计处理，研究了气泡周围液体的速度分布。结果表明：（1）气泡周围流场可分为边界层、主流区和过渡区。(2)速度梯度与气泡附近的气体流速条件无关。(3)气泡雷诺数可以很好地表征气泡周围的流动结构。(4)当气泡受到领先气泡的尾流影响时，流动被领先气泡脱落的涡流高度搅动。气泡在液体中上升时，气泡边界层内的流动仍保持层流状态。广泛的数据处理方法已经开发，提供了可能性，以评估局部瞬时空隙率，气泡上升速度和气泡体积，以及它们的时间和横截面的平均值。这些平均值用于推断表观气体速度的局部分布。（1）将所提出的算法应用于矩形通道（<UG>= 0-5 mm/s，<UW>= 0-25 mm/s和两种空气喷射结构）中的泡状流。通过与VIP提供的数据进行比较，发现空泡率预测的准确性在5%以内。(2)重建的体积流量显示出的不确定性的顺序高达20%的真实气体速度低于300毫米/秒和高达30%以上。