风速变化对竹湖流场结构影响的数值试验

NUMERICAL EXPERIMENTS ON INFLUENCE OF WIND SPEED ON CURRENT IN LAKE

利用EcoTaihu生态模型中的压缩坐标系下三维水动力学子模型,对4种吞吐流量(换水周期分别为36d、7.2d、3.6d、35h),东、西、南、北风向,不同风速的风场作用下的浅水湖泊进行了数值模拟,分析比较了不同风速作用下湖泊分层流场及垂向平均流场结构的差异。结果表明,随着风速的增大,湖泊垂向平均流场逐渐由受吞吐流控制转变成受风生流场控制;在此转变过程中存在着临界风速值,当风速大小超过该值时,流场结构发生明显的改变;风向和吞吐流量是影响临界风速值大小的主要因素。风速变化对稳定状态的湖泊表层、次表层流场有较大影响,而对底层和次底层影响不大。在水深水平变化较大的区域,垂直平均流场结构对风速变化的响应较为敏感,易形成环流,浅水区垂向平均流向和风向一致,深水区则和风向相反;水深变化较小的水域,流场结构对风速变化的响应则较为迟钝。

Numerical experiments on wind influence on water current in Zhuhu Lake （or Bamboo Lake in Chinese, an artificial lake within a residential area of Shanghai） were conducted with 3-D hydrodynamic EcoTaihu Model （partially）. The study aims at understanding the movement and function of the lake for developing the lake in an environmental friendly manner. East, west, north, and south winds were simulated with speed from 0 to 11.0 m/s. Comparisons of verti- cal-averaged current field among the winds of different speeds in the four directions showed that the wind speed had great influences on the current. For each wind direction, there is a critical speed, below which the current was controlled by water flows inlet and outlet, while above which the current is mainly dominated by wind. Moreover, when wind speed reached certain speed, two or more circumfluences were formed. In the area of sharp depth change, the pattern of average current field varies sensitively with wind speed change, while in the area of flat and gentle bottom, insensitively. The current direction in shallow water was consistent with the direction of the wind, while against the wind direction in deeper water and responded slowly.