Improvement of vortex shedding control and drag reduction on a square cylinder using twin plates

This study aims to numerically investigate the optimal conditions for fluid flow control around a single square cylinder with the help of a pair of attached flat plates. It is comparatively a new approach for controlling fluid flows as compared to the traditional solo plate flow control devices. The plates are attached adjacent to the both rear corners of the cylinder and their length (l) is varied from 0.1 to 4 times size of main cylinder while fixing the height (h) at 0.2. By varying the length, the plates manage to control the flow gradually. This study discusses how a steady wake can be achieved through control plates. Results indicate that the flow regime changes from unsteady to transitional at l=2.7 while for l>3.1 the steady flow appears. The streamlines visualizations reveal different flow structures termed as the oval-eye vortex, chain necklace vortex, sphere vortex, hair pin vortex and wooden eyes vortex-like structures. Among these the oval-eye vortex structure is found to have higher flow induced forces and shedding frequencies while the wooden eyes vortex structure is found to have minimal flow induced forces and shedding frequencies. After l=3.2, the plates’ efficacy is proven by a 100% reduction in Strouhal number, root-mean-square values of lift coefficient and amplitudes of lift and drag coefficients. This study reveals that l=3.2 is the best optimal value of plates length for complete wake and fluid forces control.