Abstract Experiments were conducted in a water flume using Particle Image Velocimetry (PIV) to study the evolution of the vortical structures in the wakes of four types of screen cylinders at a Reynolds number of about 3200. The results were compared with that of a bare cylinder. The screen cylinders were made of stainless steel screen meshes of various porosities (37%, 48%, 61% and 67%) rolled into cylindrical shapes. Smoke wire flow visualisations in a wind tunnel were also conducted in support of the PIV tests. Depending on the porosity of the screen mesh, two vortex formation mechanisms for the screen cylinder wakes were identified. One was associated with wake instability and the other was associated with shear-layer (Kelvin-Helmholtz) convective instability which involved merging through pairing and tripling of small-scale vortices within the shear layers. The former was responsible for the formation of large-scale vortices in the bare cylinder and the screen cylinder wakes with 37% and 48% porosities, while the latter was responsible for the screen cylinder wakes with 61% and 67% porosities. The results also showed that with increasing porosity, the vortex formation region was extended farther downstream and the Reynolds shear stress, the Turbulent Kinetic Energy (TKE) and vortex intensity were decreased constantly.

中文翻译：

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基于PIV的筛筒尾流结构实验研究

摘要 使用粒子图像测速仪 (PIV) 在水槽中进行实验，研究了雷诺数约为 3200 的四种筛筒尾流中涡旋结构的演变，并将结果与​​裸筒进行了比较。 . 筛筒由各种孔隙率（37%、48%、61%和67%）的不锈钢筛网制成，卷成圆柱形。为了支持 PIV 测试，还进行了风洞中烟丝流的可视化。根据筛网的孔隙率，确定了筛筒尾流的两种涡流形成机制。一个与尾流不稳定性有关，另一个与剪切层（开尔文-亥姆霍兹）对流不稳定性有关，其中涉及通过剪切层内小尺度涡旋的配对和三倍合并。前者负责在裸柱和筛柱尾流中形成大尺度涡流，孔隙率为 37% 和 48%，而后者负责筛柱尾流，孔隙率为 61% 和 67%。结果还表明，随着孔隙度的增加，涡流形成区域向下游延伸，雷诺剪应力、湍流动能（TKE）和涡流强度不断降低。前者负责在裸柱和筛柱尾流中形成大尺度涡流，孔隙率为 37% 和 48%，而后者负责筛柱尾流，孔隙率为 61% 和 67%。结果还表明，随着孔隙度的增加，涡流形成区域向下游延伸，雷诺剪应力、湍流动能（TKE）和涡流强度不断降低。前者负责在裸柱和筛柱尾流中形成大尺度涡流，孔隙率为 37% 和 48%，而后者负责筛柱尾流，孔隙率为 61% 和 67%。结果还表明，随着孔隙度的增加，涡流形成区域向下游延伸，雷诺剪应力、湍流动能（TKE）和涡流强度不断降低。