Effect of Random Noise and Gaussian Noise Forcing on the Wake of a Circular Cylinder
Type of DegreeMaster's Thesis
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Flow over a bluff body has been a topic of extensive investigation, due to a variety of engineering problems such as vortex induced vibrations, unsteady forces and noise associated with the periodic flow in the wake. The effect of random and Gaussian noise forcing on the control and suppression of periodic von Karman vortex shedding in the wake of a circular cylinder was investigated using internal acoustic excitation, at a Reynolds number of 12,000. The von Karman vortices in the wake superimposed with the small strength vortices ejected from a slit due to forcing, resulted in acceleration of the shear layers, consequent delay in flow separation, shrinkage of the wake, and reduction in drag. Asymmetry in the wake was observed in cases involving single slit forcing, the effect of which was found maximum when the slit angle was in proximity to the flow separation point on the cylinder surface. Random noise forcing resulted in a maximum drag reduction of 47%, whereas Gaussian noise forcing resulted in 36% maximum drag reduction. A hybrid flow control strategy implementing the combination of noise forcing and a trip strip at the forward stagnation point were also investigated. A maximum drag reduction of 24% by random noise forcing and 27% by Gaussian noise forcing was observed in this flow control technique.