Boundary Layer Transition Induced by a Von Karman Vortex Street Wake

A study has been made of the process of laminar to turbulent transition induced by a von Karman vortex street wake, in the boundary layer on a flat plate. The boundary layer developed under zero pressure gradient conditions while the vortex street was generated by a cylinder positioned in the free stream. Hot-wire measurements over a range of Strouhal frequencies and free stream velocities were used for the identification of the transition onset. From the analysis of the experimental data, two different transition mechanisms known in the literature as ‘strong’ wake and ‘weak’ wake induced transition, could be identified. It was established that, the onset of the strong von Karman wake induced transition process was a function of the free stream velocity, the position of the cylinder with respect to the plate, the cylinder diameter, the drag coefficient and the minimum velocity in the developing wake at the streamwise position of the onset of the boundary layer transition. The end of the strong wake induced transition, was defined at the streamwise distance, where the wake of the cylinder met the wall. A correlation for the prediction of the onset of the transition was developed