Numerical study of fluid force reduction on a circular cylinder using tripping rods

A numerical investigation on the effects of small tripping rods on the fluid force reduction on a big structure has been carried out using finite volume method where a configuration of a circular cylinder with two small tripping rods symmetrically placed very near to its front surface is studied. The diameter ratio of the rods and the cylinder is set at 0.08, 0. 10 and 0. 12, and the gap between the rods and the cylinder is fixed at 0.08 of the cylinder diameter. The angular position of the rods varies from 20 degrees to 60 degrees. The effects of the tripping rods on force reduction, vortex shedding frequency and flow separation have been examined for various arrangements of the rods with Reynolds number focused on 200 for laminar flow and 5.5x10(4) for a turbulent flow. The results reveal that there exits an optimum position where the time averaged force coefficients acting on the cylinder all reach their minimum values and at the same time Stroulial number meets its maximum. At the optimum position the drag coefficient is reduced by 18% for Re=200 and 59% for Re=5.5x10(4). Further investigation with tripping rods placed near the separation points is also carried out for Re=5.5x 10(4) and a considerable drag reduction is found.