Abstract: The drag reduction for bluff body flow has high potential for application in aeronautical engineering, and it is also a hot research topic for fundamental study. In order to explore the fine flow structures and develop efficient passive flow control method for drag reduction, using high fidelity large eddy simulation, the present study numerically conducts passive flow control of drag reduction for a simplified D-shaped cylinder. Firstly, based on previous research, a small smooth circular cylinder is placed near the shear layer in the wake region of the D-shaped cylinder, and its effect on the drag reduction is numerically studied. It is found that the total drag can be reduced by 17.7%, which agrees with the experimental data very well. The predicted velocity flow fields are found to agree with the experimental results well too. Furthermore, the present study proposes a new flow control approach, i.e. to apply the grooved-surface circular cylinder to replace the previous smooth one to disturb the wake flow after the D-shaped cylinder. The numerical study is performed and it is found that the total drag can be reduced by 21.4%. The larger drag reduction confirms that the proposed flow control method can work well. At last, the Reynolds number effect is studied and three cases with different Reynolds number are carried out. The drag reduction methods with two different small cylinder disturbances work quite well at different Reynolds numbers, and the maximum drag reductions by the two small cylinder disturbances are 19.6% and 23.1%, respectively. Based on the numerical results from the large eddy simulation, the relevant flow mechanism of the drag reduction is also explored. The obtained results demonstrate that by controlling the flow fields properly, a better drag reduction method can be obtained.

Key words: Large eddy simulation;Turbulent flow around bluff body;Flow control for drag reduction;Flow separation;Reynolds number

摘要： 钝体减阻在航空航天等多个领域内具有重要的应用潜力，也是重要的基础研究热点问题。为了精确捕捉流动控制的流动细节，并发展效果优良的流动控制减阻方案，论文围绕抽象出的D型钝体，采用大涡模拟方法，开展了被动控制减阻高精度数值模拟研究。首先基于前期研究成果，对D型钝体尾迹区剪切层附近放置一个光滑小圆柱的被动减阻方法开展了数值模拟，发现总阻力减小17.7%，与试验结果吻合很好，同时数值预测的速度场分布也与试验结果吻合良好。在此基础上，进一步提出了采用齿槽型表面结构的小圆柱对D型钝体尾迹区进行扰动，并开展了数值验证，发现总阻力减小21.4%，优于前期的减阻方法。最后研究了在三种雷诺数工况下两种小圆柱扰动情况下的减阻效果，均表现出良好的减阻效果，两种小圆柱扰动下总阻力最大降幅分别为19.6%和23.1%，同时基于大涡模拟计算结果对减阻流动机理进行了探讨。上述研究结果表明，通过进一步优化流场结构，可以得到更优的流动减阻方案。

关键词: 大涡模拟;钝体绕流;流动控制减阻;流动分离;雷诺数