Initial Stage of a Three-Dimensional Vortex Structure Existing in a Two-Dimensional Boundary Layer Separation Flow : Observation of Laminar Boundary Layer Separation over a Circular Cylinder by Flow Visualization

Abstract

Although it is generally known that the Karman vortex street consists of large-scale vortex structures with three-dimensional characteristics, the causes of the three-dimensional instability have not yet been elucidated. In this study, the three-dimensional characteristics of boundary layer separation around a circular cylinder were observed in water flow by using the laser light sheet technique in the range of Reynolds numbers from 170 to 1340 in a closed-circuit water channel and a towing water tank. As a result, it was determined that the three-dimensional instability of wake flow is based on the three-dimensional characteristics of boundary layer separation around a circular cylinder, which varies with the Reynolds number of the flow.