Effect of three dimensional forcing on the wake of a circular cylinder

Abstract

The periodic wake of a circular cylinder was investigated with a three dimensional disturbances,introduced in the flow field through two sinusoidal slits located on two diametrically opposite direction on the cylinder surface. Two speakers were used for periodic forcing. Experiments were conducted at Reynolds number of 24,000 and 45,000. It was found that an excitation frequency which was twice the shedding frequency was able to eliminate the shedding peak. At lower Reynolds number the drag measurement showed that maximum drag reduction was achieved when the excitation frequency was almost four times the natural shedding frequency. The basic mechanism of cancellation of shedding peak was found to be linked to the introduction of three dimensional disturbance which disrupted the formation of Karmann vortex street. This resulted in a distribution of energy from the shedding peak to smaller scales. The introduction of three dimensional disturbance accelerated the separating shear layers which narrowed the wake and made it uniform in terms of mean velocity. v