Flow pattern and velocity field distribution of cross-flow around four cylinders in a square configuration at a low Reynolds number

The flow around four cylinders in a square configuration with a spacing ratio of 4 and at a Reynolds number of 200 were investigated using laser-induced fluorescence (LIF) visualization and particle image velocimetry (PIV) for angles of incidence ranging from alpha = 0degrees to 45degrees at a 5degrees interval. Several distinct flow patterns were observed. Dependent on alpha, the flow was classified into three basic flow regimes. Each regime has its own dominant flow pattern and could lead to different problems. Two distinct flow patterns, which could lead to strong flow-induced vibration, were observed in this experiment. One is the impingement of oncoming vortices on the cylinders directly. The other is the formation of a jet flow between the near wake (or alternatively known as stagnation wake) of the upstream cylinder and downstream cylinder and such a jet flow is most prominent at alpha = 15degrees. These experimental results can be used to validate numerical simulation methods developed to investigate flows around cylinder arrays. (C) 2003 Elsevier Science Ltd. All rights reserved.