应用E-ε湍流动能闭合湖泊热力学过程模型对东太湖湖-气交换的模拟

The lake-air exchange simulation of a lake model over eastern Taihu Lake based on the E-ε turbulent kinetic energy closure thermodynamic process

  • 摘要: 采用考虑沉水植物影响的E-ε湍流动能闭合湖泊热力学过程模型,模拟2013年8月东太湖湖-气交换过程,并利用太湖的站点观测数据对模型进行了验证。太湖水温的模拟值与观测值吻合较好,模型计算的各层水温与观测值相比,均方根误差均未超过1℃。同时模型也较好地模拟出太湖表面感热通量和潜热通量,潜热通量的模拟值与观测值的标准差为54.7 W/m2。由于湖水较浅,太湖的水温层结会明显受到天气状况的影响。晴朗小风条件下的湖水呈现显著的热分层现象,当风速为0.8 m/s,高层和底层的温差达到7.9℃。大风天气条件驱动较强的水体湍流混合,水温的热分层消失,风速为12 m/s,湖泊上层与底层的水温差仅0.12℃。此外,模拟结果较好地呈现出了东太湖沉水植物的存在通过增大湖体消光系数,减小到达湖体内部的热量,并增加对湖水的阻力,影响湖体中湍流动能的分布,并进而影响湖水温度的分布。综上所述,该模型能够较好地模拟出浅水大湖湖-气交换的过程。

     

    Abstract: A lake model based on the E-ε turbulence closure thermodynamic process combined with the effect of submersed macrophytes is adopted to simulate lake-air exchanges over eastern Taihu Lake in August 2013. The observational data collected at the station over the Taihu Lake are used to verify the model results. The simulated water temperature and sensible and latent heat fluxes are in good agreement with observations. RMSEs of water temperature and sensible heat flux are less than 1℃ and 54.7 W/m2, respectively. Because the lake is shallow, the stratification of the water temperature can be easily affected by weather conditions. The thermal stratification is significant under sunny condition with weak winds. The temperature difference between the lake surface and the bottom of the lake is 7.9℃ when the wind speed is 0.8 m/s. High wind speeds can drive strong vertical mixing in the lake, and lead to the disappearance of the thermal stratification. When the wind speed is 12 m/s, the temperature difference between the lake surface and the bottom of the lake is only 0.12℃. Submerged macrophytes can increase the extinction coefficient, reduce the internal heat in the lake, and add resistance to the movement of water, and subsequently influence the distribution of the turbulence kinetic energy and water temperature. In summary, this model can well simulate the lake-air exchange processes over the shallow lake.

     

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