| dc.description.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.
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