Statistics of surface renewal of passive scalars in free-surface turbulence
Statistics of surface renewal of passive scalars in free-surface turbulence
复制标题
自由表面湍流中被动标量表面更新的统计
DOI：
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发表时间：
2011
影响因子：
3.7
通讯作者：
T. Igusa
中科院分区：
文献类型：
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作者：
A. Kermani;Hamid R. Khakpour;Lian Shen;T. Igusa
我们进行直接数值模拟来研究自由表面湍流中气体和热量作为被动标量的传输。我们的分析重点是表面流体颗粒的表面年龄，即自上次表面更新以来经过的时间。利用流体颗粒的拉格朗日追踪与热扩散分析相结合，我们能够直接量化表面年龄，以说明界面传递不同阶段的标量特征。结果表明，在地表更新早期，与上升流相关的垂直平流极大地增强了地表气体通量；当大部分界面气体转移发生时，随机表面更新模型在此阶段不适用。流体粒子离开上升流区域后，可能会立即进入附近的下降流区域，此时气体通量急剧减少，但表面温度变化较小；或者，流体粒子可能会沿着表面行进一段时间，然后被下降流吸收，其中表面温度由于扩散持续时间长而发生显着变化，并且气体通量也减少。为了进一步了解表面速度和标量之间的关系，我们使用聚类和非线性回归对上升流进行统计分析。通过这种分析，我们能够提供与表面散度、温度和气体通量相关的偏斜概率密度函数的定性和定量描述，支持我们对表面更新和表面年龄的基于物理的研究。
We perform direct numerical simulation to study the transport of gas and heat as passive scalars in free-surface turbulence. Our analysis focuses on the surface age of surface fluid particles, i.e. the time elapsed since the last surface renewal they experienced. Using Lagrangian tracing of fluid particles combined with heat diffusion analysis, we are able to directly quantify surface age to illustrate scalar characteristics at different stages of interfacial transfer. Results show that at the early stage of surface renewal, vertical advection associated with upwellings greatly enhances surface gas flux; random surface renewal model does not apply at this stage when most of the interfacial gas transfer occurs. After a fluid particle leaves the upwelling region, it may enter a nearby downwelling region immediately, where the gas flux is sharply reduced but the variation in surface temperature is small; alternatively, the fluid particle may travel along the surface for some time before it is absorbed by a downwelling, where the surface temperature has changed significantly due to long duration of diffusion and the gas flux is also reduced. To gain further insight into the relationships between surface velocity and scalar quantities, we perform a statistical analysis of upwellings using clustering and nonlinear regression. With this analysis, we are able to provide qualitative and quantitative descriptions of the skewed probability density functions associated with the surface divergence, temperature and gas flux that support our physics-based investigation of surface renewal and surface age.