Study of vortex dislocations in the wake of a flat plate with finite thickness

Wake structures of a flat plate with finite thickness are studied using the rake of X-wires techniques. Parallel and oblique shedding modes in the wake flow are investigated. These modes depend on the flat plate end conditions. In the present paper, we demonstrate that manipulation of the end conditions yields vortex dislocations that appear at the same location. By manipulating the end conditions, vortex chain structures branching inside the dislocations are analyzed by means of pseudoflow visualization of the X-wire:rake data. The appearance of branching vortex chains is due to misfit between two oblique vortex shedding cells. Power spectra of velocity fluctuations show growth of the low-frequency mode due to subtraction of the two fundamental shedding modes of different frequency across the span. The small difference between the two fundamental shedding modes explains the large intermittent velocity irregularities in the large-scale structure downstream that occur in natural transition.