以2×600 MW直接空冷机组为例，利用CFD软件对其空冷岛外部流场进行数值模拟。分析了不同高度的下挡风墙对直接空冷凝汽器风机风量的影响。在风速大于7 m/s时，空冷凝汽器换热效率的降低是热风回流与“倒灌”现象综合作用的结果。提出了加装曲面下挡风墙的方案，并计算了加装不同高度的曲面下挡风墙对背风面风机的风量和风机换热效果的影响。结果表明，最佳下挡风墙高度为85 m，此时的风机风量达到最大，换热效果最好，前2排风机平均换热效率比没有安装下挡风墙时提高了1703%。研究成果为进一步完善空冷岛的结构设计提供了理论依据。

The external flow filed of the air-cooled island is numerically simulated by CFD for a 2×600 MW direct air-cooled unit. For the wind speed higher than 7 m/s, the combination of hot air recirculation and downdraught of the air cooled condenser results in the reduction of heat exchange efficiency. Therefore, fixing lower windbreak with curved surface upon direct air-cooled condenser is considered. Furthermore, the effects of lower windbreak height on average heat exchange efficiency and flow capacity of fans are discussed. It is shown that the optimum height of the windbreak is 85 m, where the fan flow and heat exchange reach to the maximum. Especially the average heat exchange efficiency of the first two lines of fans increases 1703% than that without the lower windbreak. It provides theoretical evidence for the structural design and optimization of the air-cooled island.