Drag Reduction on a Square Cylinder using Multiple Detached Control Cylinders

A two-dimensional numerical simulation for flow over a main cylinder with detached controlling cylinders placed at different position is performed through Lattice Boltzmann Method (LBM) to reduce fluid forces. For this study the Reynolds number (Re) is fixed at 160, while gap ratio between these cylinders are taken in the range from 0.5 to 8. The results yield in terms of vorticity, time-series analysis of drag and lift coefficients, power spectra of lift coefficients and force statistics. Depending on gap spacing, flow is classified into four different patterns, called as (i) single blender body, (ii) shear layer reattachment, (iii) fully developed flow and (iv) vortex suppression fully developed flow patterns. In comparison of all three configurations, it is examined that the maximum value of Cdmean and Strouhal number occurs for downstream configuration. Whereas, upstream and dual configuration play a vital role to reduce forces and to suppress vortex shedding. The maximum reduction found in mean drag coefficient for downstream, upstream and for dual configuration is 8.3%, 51% and 50.8%, respectively. Whereas, the reduction in Clrms values for all three configurations is 84.4%, 58.2% and 86.4%, respectively.