Wake flows behind two dimensional bodies are mainly dominated by two coherent structures, namely the Karman-Benard vortices and the streamwise vortices, also referred to as rolls and ribs respectively. The three dimensional wake instabilities lead to distinct instability modes (mode-A, mode-B and mode-C or mode-S) depending on the flow Reynolds number and geometric shape. The present investigation explores the mechanism in which the flow transitions to three dimensionality in the near wake of a profiled leading edge and blunt trailing edge body. A combination of Planar Laser Induced Fluorescence visualizations and Particle Image Velcoimetry measurements are conducted in the Reynolds numbers ranging from 250 to 550. The results indicate that three instability modes (mode-A, mode-B and mode-C) appear in the wake transition to three dimensionality, and their order of appearance does not occur through the traditional route as observed in circular cylinder flows. It is found that mode-C instability with a spanwise spacing of 2.4D dominates the near wake development.

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