Numerical analysis of the wake of complex-shaped snow particles at moderate Reynolds number
Numerical analysis of the wake of complex-shaped snow particles at moderate Reynolds number
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DOI：
10.1063/5.0064902
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发表时间：
2021-10
影响因子：
4.6
通讯作者：
G. Tagliavini;Mark W. McCorquodale;C. Westbrook;M. Holzner
中科院分区：
文献类型：
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作者：
G. Tagliavini;Mark W. McCorquodale;C. Westbrook;M. Holzner
气候模型参数化很大程度上依赖于降雪量的预测，而降雪量又取决于雪花在空气中下落的运动。由于粒子的不规则形状，这些粒子的下落姿态是复杂的，会产生蜿蜒和湍流的尾迹，并产生复杂的轨迹。这也会对粒子所经历的阻力产生影响。特别是对于接近地面落下的大雪粒，斯托克斯动力学不适用，并且阻力系数对雷诺数的依赖性变得非线性。这种趋势源于雪花与周围空气之间复杂的相互作用。我们使用经过验证的固定雪花周围气流延迟分离涡流模拟模型，结合自由落体 3D 打印雪花类似物的实验观察，研究复杂形状雪颗粒的尾流。这种新颖的方法使我们能够分析尾流拓扑并分解其动量通量，以通过与实验进行比较来研究形状和尾流对阻力系数的影响及其对坠落姿态的影响。在低 Re 条件下，分离涡环的存在与颗粒孔隙率有关，并导致阻力系数增加。在中等流动状态下，颗粒平坦度会影响尾流中的剪切层分离和动量损失，而在高Re下，尽管不同动量通量项的贡献不同，但在测试的几何形状中阻力系数几乎具有相同的值。这些结果代表着朝着更深入地了解复杂形状颗粒的阻力又迈出了一步。
Climate model parametrization relies strongly on the prediction of snow precipitation, which in turn depends upon the snowflakes falling motion in air. The falling attitudes of such particles are elaborate because of the particles' irregular shapes, which produce meandering and turbulent wakes and give rise to convoluted trajectories. This also has an impact on the drag experienced by the particle. Especially for large snow particles falling close to the ground, Stokesian dynamics is not applicable, and the dependency of drag coefficient on Reynolds number becomes non-linear. This trend arises from the complex interaction between snowflakes and the surrounding air. We investigate the wake of complex-shaped snow particles using a validated delayed-detached eddy simulation model of airflow around a fixed snowflake, combined with experimental observations of free-falling, 3D-printed snowflake analogs. This novel approach allows us to analyze the wake topology and decompose its momentum flux to investigate the influence of shape and wake flow on the drag coefficient and its implications on falling attitudes by comparison with experiments. At low Re, the presence of separated vortex rings is connected to particle porosity and produces an increase in the drag coefficient. At moderate flow regimes, the particle flatness impacts the shear layer separation and the momentum loss in the wake, while at high Re the drag coefficient has almost the same value among the tested geometries although the contribution of different momentum flux terms differs. These results represent a further step toward a deeper understanding the drag of complex-shaped particles.