Characteristics of the Flow around Two Circular Cylinders Arranged in Tandem : 2nd Report, Unique Phenomenon at Small Spacing

In the previous paper, three flow patterns were found at small spacing between two cylinders arranged in tandem as follows: the first is a flow without reattachment of the shear layer separated from the upstream cylinder, the second is an unstable flow and the third is an unique flow like that the frequency of the vortex shedding is nearly constant regardless of the free stream velocity. The purpose of this paper is to investigate the conditions of the occurrence of the above flow patterns and their flow characteristics in more detailed. It becomes clear that the unstable flow is caused by the intermittent reattachment of the shear layer onto the downstream cylinder, the unique phenomenon on the Strouhal numner occurs in the range of 2.5×104≤Re≤6.5×104 and is a transition phenomenon due to interference between the two cylinders. Beyond Re=6.5×104, the Strouhal number becomes again constant.