Aspects of Flow Structure During a Cylinder Wake-Induced Laminar/Turbulent Transition

Abstract

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 occurring coherent structures. The wake was generated by a horizontal cylinder positioned in the freestream and upstream of the flat plate's leading edge. An X-type hot-wire probe measured the stream wise and normal-to-the-wall velocity components, whereas a gradient hot-wire probe, located in the cylinder's wake and at the same stream wise position as the X-type hot-wire probe, detected the passage of the von Karman vortices. From the simultaneously acquired velocity and gradient signals, the intermittency factor distribution and cross-correlation functions, combined with a quadrant-splitting analysis, were computed. Furthermore, an ensemble-average technique was applied to the signals. The analysis of the signals revealed that during the transition a secondary vortical structure occurs near the wall. Turbulent kinetic energy transfer to and from the wall during the transition was evaluated