Abstract
Flow field in the gap space between two circular cylinders forming a cross was visualized under the Reynolds number of about 1200 by using a method of dye injection. As the results, the various patterns of necklace vortex system are produced, depending on the gap space, G, between two cylinders. In the case of G/d=0, the boundary layer on the surface of the upstream cylinder separates and rolls up as a main necklace vortex near the symmetrical plane. In the case of G/d=0.3, the necklace vortex system consisting of four vortices is formed, and surrounds the downstream cylinder.
