Dynamic behavior of binary water droplets approaching each other in cloud by the improved two-phase lattice Boltzmann simulation
Dynamic behavior of binary water droplets approaching each other in cloud by the improved two-phase lattice Boltzmann simulation
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DOI：
10.1299/transjsme.18-00023
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发表时间：
2018
期刊：
影响因子：
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通讯作者：
Jumpei Sawada;M. Yoshino;Kosuke Suzuki
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文献类型：
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作者：
Jumpei Sawada;M. Yoshino;Kosuke Suzuki
采用改进的两相晶格玻尔兹曼方法和连续表面力（CSF）模型模拟了云中二元水滴相互接近的动态行为。该方法不需要求解压力泊松方程，使我们能够准确、高效地计算高密度比的两相流。在本研究中，我们研究了雷诺数Re、韦伯数We、冲击参数B（两个液滴中心之间的相对距离）和液滴尺寸比对液气密度比为800的二元液滴行为的影响。我们首先模拟气体中的静止液滴以证实本方法的有效性。接下来，我们模拟两个大小相等的液滴的偏心接近，并研究雷诺数和韦伯数的影响。可以看出，在 We∼O(10−2) 的低韦伯数下，两个相同尺寸的液滴接近时有两种类型的行为，即合并和偏离。在这个韦伯数区域中，发现尽管 B ≤ 1.0，它们在 Re ≲ O(1) 的低雷诺数下仍会彼此偏离，而在 Re ≳ O(10) 的较高雷诺数下发生碰撞和随后的合并。我们最终模拟了两个具有不同尺寸比例的不等尺寸液滴的接近。研究发现，由于速度场和液滴变形的不对称，液滴的行为与等尺寸液滴的情况不同。此外，较小的液滴往往比较大的液滴更明显地偏离其原始路径。
Dynamic behavior of binary water droplets approaching each other in cloud is simulated by the improved two-phase lattice Boltzmann method with the Continuum Surface Force (CSF) model. This method does not need to solve the pressure Poisson equation and enables us to calculate two-phase flows with high density ratio accurately and efficiently. In this study, we investigate the effects of the Reynolds number Re, the Weber number We, the impact parameter B (the relative distance between the centers of two droplets), and the droplet size ratio on the behavior of the binary droplets for liquid–gas density ratio of 800. We first simulate a stationary liquid droplet in a gas to confirm the validity of the present method. We next simulate off-center approach of two equal-size droplets and investigate the effects of the Reynolds number and the Weber number. It is seen that at low Weber numbers of We ∼ O(10−2), there are two types of behavior during approach of two equal-size droplets, namely coalescence and deviation. In this Weber number region, it is found that they can deviate from each other at low Reynolds numbers of Re ≲ O(1) in spite of B ≤ 1.0, whereas collision and subsequent coalescence occur at higher Reynolds numbers of Re ≳ O(10). We finally simulate approach of two unequalsize droplets with various size ratios. It is found that the behavior of the droplets is different from that in the case of the equal-size droplets owing to asymmetric velocity field and droplet deformation. In addition, the smaller droplet tends to deviate from its original path more significantly than the larger droplet.