Turbulence kinetic energy budget in bubbly flows in a vertical duct
Turbulence kinetic energy budget in bubbly flows in a vertical duct
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DOI：
10.1007/s00348-011-1109-z
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发表时间：
2012-03
影响因子：
2.4
通讯作者：
S. Hosokawa;Takashi Suzuki;A. Tomiyama
中科院分区：
文献类型：
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作者：
S. Hosokawa;Takashi Suzuki;A. Tomiyama
了解气液两相泡状流的湍流动能收支是发展和完善泡状流湍流模型的必要条件。本文采用基于光漂白反应的分子标记测速技术，对垂直方形管道中含有亚毫米气泡的湍流泡状流进行了实验研究，以检验k-ε模型对泡状流的适用性。讨论了气泡对TKE收支的影响，并对标准和低雷诺数k-ε模型进行了先验检验，以检验这些模型对泡状流的适用性。得到的主要结论如下：（1）光漂白分子标记测速技术可用于湍流模型的验证。(2)气泡的存在增大了近壁区的液体速度梯度，从而提高了TKE的产生和耗散速率。(3)k-ε模型能合理地评价泡状流中TKE的产率。(4)由于气泡的扩散调制具有不同的特性，由于剪切诱导湍流的扩散增强。因此，k-ε模型不能准确地计算泡状流近壁区的扩散速率。(5)k-ε模型代表了泡状流中ε的产生、耗散和扩散速率的变化趋势，但ε方程的定量验证还需要更精确的实验数据。
Understanding turbulence kinetic energy (TKE) budget in gas–liquid two-phase bubbly flows is indispensable to develop and improve turbulence models for the bubbly flows. In this study, a molecular tagging velocimetry based on photobleaching reaction was applied to turbulent bubbly flows with sub-millimeter bubbles in a vertical square duct to examine the applicability of thek–ε models to the bubbly flows. Effects of bubbles on TKE budget are discussed and a priori tests of the standard and low Reynolds numberk–ε models are carried out to examine the applicability of these models to the bubbly flows. The conclusions obtained are as follows: (1) The photobleaching molecular tagging velocimetry is of use for validating turbulence models. (2) The bubbles increase the liquid velocity gradient in the near wall region, and therefore, enhance the production and dissipation rates of TKE. (3) Thek–ε models can reasonably evaluate the production rate of TKE in the bubbly flows. (4) The modulations of diffusion due to the bubbles have different characteristics from the diffusion enhancement due to shear-induced turbulence. Hence, thek–ε models fail in evaluating the diffusion rate in the near wall region in the bubbly flows. (5) Thek–ε models represent the trends of the production, dissipation, and diffusion rates of ε in the bubbly flow, although more accurate experimental data are required for quantitative validation of the ε equation.