北方浅水湖泊冬季结冰对风生流的影响

为了研究北方浅水湖泊冬季结冰对风生流的影响,采用MIKE21构建山东省聊城市东昌湖水动力学模型,分析真实风场作用下6种风应力拖曳系数对应的模拟流速与实测数据的差异,进一步讨论了冰盖面积对模拟结果产生的影响。结果表明,风应力拖曳系数为随风速连续变化比设置为常数模拟精度提高20%左右,其中采用微风条件下的风应力拖曳系数表达式模拟效果最好。此外,冬季水体结冰对风生流数值模拟影响较大,尤其是在被冰盖所覆盖的水域,风应力对水体流动的作用减弱甚至被抵消。与传统的风生流模拟相比,在北方浅水湖泊冬季风生流模拟中,引入冰场或是对风应力拖曳系数进行相应调整是有必要的。

Study on wind-driven flow under the influence of water freezing in winter in a northern shallow lake

Six empirical formulae of the wind drag coefficient were considered in a MIKE21 hydrodynamic model to study properties of wind-driven flow in a shallow lake in the northern city (Dongchang Lake in Liaocheng, Shangdong, China) under a real wind condition. Moreover, the influence of ice cover area on simulated result was also analysed. The results showed that the accuracy was improved about 20% when the wind drag coefficient was varied with real wind field than when it was constant. That is, the model with real wind could accurately describe the wind-driven flow process of the Dongchang Lake. Among the six formulae of the wind drag coefficient, the one proposed under breeze condition was best. Freezing water has significant effected on numerical simulation of wind-driven flow, especially in the zone of ice cover. The influence of wind stress on water flow has been weakened or counteracted under water freezing. Compared with the traditional wind-driven flow simulation, it was necessary to consider ice condition or to adjust the wind drag coefficient in MIKE21 in a northern shallow lake. The results might give a reference for the water resources management in a northern shallow lake.