A numerical study of flow fields of lobed hailstones falling in air
A numerical study of flow fields of lobed hailstones falling in air
复制标题
空气中叶状冰雹流场的数值研究
DOI：
10.1016/j.atmosres.2015.02.013
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发表时间：
2015
影响因子：
5.5
通讯作者：
Chen Wang
中科院分区：
文献类型：
--
作者：
Pao K. Wang;C. Chueh;Chen Wang
研究了6颗直径为1 ~ 10 cm的裂状降雹的流场特性。流场是通过数值求解时间相关的Navier-Stokes方程得到的，通过一组新提出的数学表达式，我们可以精确地表示它们的形状，这些形状可以很容易地通过立体光刻进行模拟。雷诺数范围为9560 ~ 388000，认为这是接近实际物理范围的。计算得到的流场具有流迹模式、垂直速度、压力分布和涡度场等特征。计算结果表明，当相同大小的6个裂叶冰雹的涡流长度几乎相同时，当一个冰雹上的裂叶越多、越长时，再循环气泡内的涡流更加混乱。在雷诺数约为25000 ~ 122000的范围内，球形冰雹的阻力系数高于三种短裂冰雹，而我们考虑的大多数长裂冰雹的阻力系数高于球形冰雹。然而，与前人的实验数据相比，光滑球形霰和冰雹的阻力系数都比本文所考虑的几乎所有短裂雹和长裂雹都要大得多。
The characteristics of the flow fields around six falling lobed hailstones of diameters 1 to 10 cm are studied. The flow fields are obtained by numerically solving the time-dependent Navier–Stokes equations for flow past the six lobed hailstones created through a set of newly proposed mathematical expressions allowing us to precisely represent their shapes that can be easily meshed afterwards through stereolithography for the simulations performed herein. The range of Reynolds numbers is from 9560 to 388,000, which is believed to be close to the realistic physical range. The computed flow fields are characterized in terms of the streamtrace pattern, vertical velocity, pressure distribution, and vorticity fields. The computed results demonstrate that while the eddy lengths for the six lobed hailstones of equal size are almost the same, with more and longer lobes on a hailstone, the eddies inside the recirculation bubble shed more chaotically. In comparison with our previous numerical work, the spherical hailstones have higher drag coefficients than the three short lobed hailstones in the range of Reynolds numbers roughly between 25,000 and 122,000 while most long lobed hailstones we consider have greater drag coefficients than the spherical ones. However, compared with previous experimental data by others, the smooth spherical graupel and hailstone are both highly greater in drag coefficient than almost all the short and long lobed hailstones considered herein numerically.