Aspects of flow structure during a cylinder wake-induced laminar/turbulenttransition

The process of a strong wake-induced laminar/turbulent transition on a flat -plate boundary layer was investigated from the point of view of the occurr ing coherent structures. The wake was generated by a horizontal cylinder po sitioned in the freestream and upstream of the flat plate's leading edge. A n X-type hot-wire probe measured the streamwise and normal-to-the-wall velo city components, whereas a gradient hot-wire probe, located in the cylinder 's wake and at the same streamwise position as the X-type hot-wire probe, d etected the passage of the von Karman vortices. From the simultaneously acq uired velocity and gradient signals, the intermittency factor distribution and cross-correlation functions, combined with a quadrant-splitting analysi s, were computed. Furthermore, an ensemble-average technique was applied to the signals. The analysis of the signals revealed that during the transiti on a secondary vortical structure occurs near the wall. Turbulent kinetic e nergy transfer to and from the wall during the transition was evaluated.