A new method for large-eddy simulations of clouds with Lagrangian droplets including the effects of turbulent collision
A new method for large-eddy simulations of clouds with Lagrangian droplets including the effects of turbulent collision
复制标题
一种包含拉格朗日液滴的云大涡流模拟的新方法，包括湍流碰撞的影响
DOI：
10.1088/1367-2630/14/6/065008
复制
发表时间：
2012
影响因子：
3.3
通讯作者：
S. Raasch
中科院分区：
文献类型：
--
作者：
Theres Riechelmann;Y. Noh;S. Raasch
本文介绍了一种新的拉格朗日云模型（LCM），该模型采用大涡模拟来模拟流场，并将液滴视为响应于模拟流场的拉格朗日粒子。为了处理云内的极大数量的液滴，引入了超级液滴的概念，超级液滴表示大量相同尺寸的真实的液滴，并且贡献的真实的液滴的数量被称为加权因子。提出了一种新的实现液滴碰撞/聚并的方法，该方法通过改变超液滴的半径和权重因子来表征液滴光谱的变化，同时保持超液滴的数目不变.使用一个理想化的单云和信风积云，LCM再现浅积云的一般特征与传统的散装模式。液滴光谱的LCM模拟，使用碰撞内核与湍流的影响，也显示出与光谱箱模型一致的模式。此外，LCM的两个模型参数，时间步长和超级液滴的数量的敏感性，检查。
In this paper, a new Lagrangian cloud model (LCM) is introduced in which the flow field is simulated by large-eddy simulation, and the droplets are treated as Lagrangian particles responding to the simulated flow field. In order to handle the extremely large number of droplets within a cloud, the concept of a super-droplet, which represents a large number of real droplets of the same size, is introduced, and the number of contributing real droplets is called the weighting factor. A novel method is developed to realize the collision/coalescence of droplets, in which the consequent variation of the droplet spectrum is represented in terms of the modification of the radius and weighting factor of super-droplets, while keeping the number of super-droplets unchanged. Using an idealized single cloud and trade wind cumuli, the LCM is shown to reproduce the general features of shallow cumulus clouds in agreement with traditional bulk models. The droplet spectrum simulated by the LCM, using collision kernels with and without the effects of turbulence, also shows a pattern consistent with the spectral bin model. Furthermore, the sensitivity of the LCM to two model parameters, the time step and the number of super-droplets, is examined.