Initial Stage of a Three-Dimensional Vortex Structure Existing in a Two-Dimensional Boundary Layer Separation Flow : Visual Observation of Laminar Boundary Layer Separation over a Circular Cylinder from the Side of a Separated Region

Abstract

It was found in the preceding study that the boundary layer separation over a circular cylinder seems to have three-dimensional separation characteristics and its three-dimensionality appears to be related to the three-dimensional wake structure. In the present study, to investigate the structures of three-dimensional boundary layer separation, the flow of the separated region over a circular cylinder was observed by means of the flow visualization technique in the range of Reynolds numbers from 230 to 1340 in a towing water tank. As a result, it was determined that the three-dimensional features of boundary layer separation over a circular cylinder were characterized by the recirculating flow in the separated region, and the relationship between three-dimensional instability in the separated region and Reynolds number was investigated.