Effect of screen geometry on the vortex formation behind a circular cylinder

The wake region of a circular cylinder with and without shroud was experimentally investigated using smoke-wire flow visualization. The shrouds were made of screen cylinders, constructed from various screen meshes. The shroud-to-cylinder diameter ratio, D/d were 1.56 and 2.0 and the flow Reynolds number based on the cylinder diameter, Red was approximately 1000. The vortex formation process was investigated and the formation length, Lf was estimated from the flow visualization. The effect of a new dimensionless parameter, β.d_w/d (where β is the screen porosity and d_w is the mesh wire diameter) on the vortex formation length was also examined. Results showed that the formation length was greater at gap ratio of 2.0 than that at 1.6, with smaller wake width observed in the former in comparison to that in the latter. The formation length also increased with increased non-dimensional parameter β.d_w/d after its critical value was reached.