To reduce the drag of a cylinder, numerical simulations and experiments for both smooth cylinder and circular cylinder with the dimpled surface are carried out in this paper. The numerical simulation focuses on the variation of pressure coefficient, skin friction coefficient, and vortex shedding strength of the smooth cylinder and the circular cylinder with the dimpled surface. It is found that the dimpled structure can effectively reduce the drag of the cylinder within a specific range of Reynolds number, and the maximum drag reduction rate reaches up to 19%. Another conclusion is that the pressure drag and skin friction drag have an essential influence on the total drag of the circular cylinder with the dimpled surface. On the other hand, the strength of vortex shedding also decreases with the decrease of cylinder drag. Then, the flow field of both cylinders is measured using the particle image velocimetry (PIV) technique, confirming that the dimpled structure can affect the velocity field, the release of vortices and the scale of the vortex. More specifically, the velocity recovery of the circular cylinder with the dimpled surface is faster than that of the smooth cylinder, and the dimpled structure delays the release of the vortex at a specific range of Reynolds number.

中文翻译：

---

表面凹面圆柱的减阻特性研究。

为了减少圆柱体的阻力，本文对光滑圆柱体和具有凹陷表面的圆柱体进行了数值模拟和实验。数值模拟的重点是光滑的圆柱体和具有凹陷表面的圆柱体的压力系数，蒙皮摩擦系数和涡旋脱落强度的变化。发现该凹坑结构可以在雷诺数的特定范围内有效地减小圆柱体的阻力，并且最大阻力减小率高达19％。另一个结论是，压力阻力和皮肤摩擦阻力对具有凹坑表面的圆柱体的总阻力有重要影响。另一方面，涡旋脱落的强度也随着汽缸阻力的减小而减小。然后，使用粒子图像测速（PIV）技术测量了两个圆柱的流场，证实了凹坑结构会影响速度场，旋涡的释放和旋涡的规模。更具体地说，具有凹坑表面的圆柱体的速度恢复比光滑圆柱体的速度恢复快，并且凹坑结构在特定的雷诺数范围内延迟了涡流的释放。