A numerical study on the ventilation coefficients of falling lobed hailstones
A numerical study on the ventilation coefficients of falling lobed hailstones
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DOI：
10.1016/j.atmosres.2019.104737
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发表时间：
2020-04
影响因子：
5.5
通讯作者：
Pao K. Wang;C. Chueh
中科院分区：
文献类型：
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作者：
Pao K. Wang;C. Chueh
通过数值求解对流扩散水汽传输方程，计算出表征在压力为 460hPa、温度为 248K 的大气中由于叶状冰雹下落运动而导致的传热/质量传递速率增强的通风系数，同时通过数值求解下落冰雹周围的非定常纳维-斯托克斯方程获得了局部气流速度。选择的大气条件使得冰雹不会变湿，并且通风系数代表干燥的冰雹条件。这里调查的冰雹直径分别为1、3、5、7和10厘米，雷诺数分别为9560至388,000。当直径为1cm时，所有情况下的通风系数几乎相同。随着尺寸的增加，差异变得更大。对于具有 36 个长叶的 10 厘米冰雹，此处计算的最高通风系数 >500。我们发现，一般情况下，叶状冰雹比相同尺寸的球形冰雹具有更大的通风效果。我们还报告了基本几何信息（即表面积和体积）与通风系数之间的联系。较大的表面积通常会导致较大的通风系数，而此处研究的石头的通风系数和体积之间不存在明确的关系。给出了通风系数与冰雹直径和施密特数的函数关系的经验公式。讨论了这些通风系数的含义。
The ventilation coefficients that characterize the enhancement of heat/mass transfer rate due to the falling motion of lobed hailstones created by a set of mathematical expressions in an atmosphere of pressure 460 hPa and temperature 248 K are computed by numerically solving the convective-diffusion water vapor transport equation while the local airflow velocities are obtained through the numerical solution of unsteady Navier-Stokes Equation around the falling hailstones. The atmospheric condition is chosen so that the hailstone is not growing wet and the ventilation coefficient represents dry hailstone condition. The diameters of the hailstones investigated here are 1, 3, 5, 7 and 10 cm with the Reynolds numbers ranging from 9560 to 388,000 respectively. The ventilation coefficients for all cases are nearly the same when the diameter is 1 cm. The difference becomes greater as the size increases. The highest ventilation coefficient calculated here is >500 for a 10 cm hailstone with 36 long lobes. We found that in general lobed hailstones have larger ventilation effect than spherical hailstones of the same size. We also report that the connection between basic geometry information (i.e. surface area and volume) and the ventilation coefficients. The larger surface area usually results in greater ventilation coefficient whereas no clear relation exists between the ventilation coefficient and volume for the stones investigated here. Empirical formulas for ventilation coefficient as a function of hailstone diameter and Schmidt numbers are given. Implications of these ventilation coefficients are discussed.