大尺度展向波形圆柱绕流流场结构的数值研究

针对大尺度展向波形圆柱绕流的减阻特性，通过大涡模拟（LES）研究波形振幅对圆柱体绕流流场结构的影响，获得波形圆柱体绕流气动性能曲线、尾迹时均流速分布和非定常涡量场分布，最后与直圆柱绕流的流场结构进行对比分析。结果表明，波形圆柱绕流的平均阻力系数小于直圆柱体绕流，流向涡的形成改变了圆柱近尾迹区的流场结构，因此，波形圆柱体尾迹涡系表现得更为紧凑，尾迹涡流得到拉伸与破裂。在亚临界雷诺数为3000时，最大阻力系数减少18.3%，最优振幅比为0.152；且波形圆柱体的升力波动大大减少，甚至得到抑制。由于波形表面会形成更稳定的三维自由剪切层，这样的自由剪切层在下游位置卷起漩涡，大大地改变了圆柱周围的流场结构。研究表明振幅比在确定波形圆柱后面的三维涡旋结构中起着至关重要的作用，并对升力波动和流动阻力的降低有着显著的影响。

Numerical investigation on the flow field around a large spanwise wavy cylinder

In this paper, in view of the drag reduction performance by the flow around a large spanwise wavy cylinder, the three dimensional large eddy simulation (LES) was used to study the influence of wave amplitude on the flow field around a cylinder in order to get the aerodynamic performance, mean velocity distribution and unsteady vorticity field distribution. Finally, the comparison between wavy cylinder and smooth cylinder was performed. The results showed that the average resistance coefficient of wavy cylinder was smaller than that of the smooth cylinder. The formation of streamwise vortices changed the flow field structure in the near wake region of the cylinder, and caused more compact wake vortex system, which was stretched and broken. At the sub-critical Reynolds number = 3000, the maximum drag coefficient was reduced by 18.3%, and the optimal amplitude ratio was 0.152. And the lift fluctuation of the wave cylinder reduced, and even was suppressed. The surface of these waves led to the formation of a more stable three-dimensional free shear layer. The free shear layer was rolled into a mature vortex at the downstream, which greatly changed the flow field around the cylinder. The research indicated that the amplitude ratio played an important role in determining the three-dimensional vortex structure behind the cylinder, which had great influence on the lift fluctuation and drag reduction.