养殖水域水面冷却对流过程的数值实验

以简单矩形水域为例,利用数值实验方法,定量探讨了具有自由水面的养殖水域由于水面冷却而引起的对流演变的过程。考虑湖泊等养殖水域的流速、水深等特征值的一般大小,数值计算中的Re、Gr、Pr分别取为8000、500000和10。计算结果显示,水面冷却对流可分为对流发生、发展和稳定三个阶段,各阶段流场及温度场的演变规律均受水面有效势能分配于扩散及对流的热输送比例变化的影响,并形成与之相对应的对流涡、温度等值线的分布特征。水面冷却对流最终形成与水深相当的大对流涡,温度等值线由对流发生当初的水平等值线几乎完全变成垂直等值线,上下层水得到充分交换。

A numerical experiment of convection course driven by surface cooling in aquatics waters

Based on a numerical experiment carried out with a simple rectangular water area as an example, the paper discussed the developing progress of convection driven by surface cooling in aquatics waters with free surface quantitatively. In view of the common characteristics of velocity, depth and other given values in lake and other aquatic waters, the values of Re, Gr, Pr could be taken of 8000, 500000 and 10 respectively. The result shows that the convection driven by surface cooling could be subdivided into three phases, i.e. the occurring phase, the developing phase and the steady phase. The development of fields of the velocity and temperature at different phases is affected by rates of the effective potential energy distributed to the diffusing and heat transporting, with convectional eddies and isotherms being formed at the same time correspondingly. Big convectional eddies were brought out by the convection driven by surface cooling, with the magnitude of their diameters being equal to the depth at the end; the distribution of isotherms changed from horizontal form at the beginning to the vertical at the end, so that the water is exchanged fully from surface to the bottom.