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Study on the Effects of Karman Vortex in Aerodynamic Forces of Rectangular Cylinders

In this study, a series of wind tunnel tests were carried out to understand the complicated bluff body aerodynamics affected by Karman vortex on 2D rectangular cylinders with various side ratios, B/D=0.3~15. Based upon the aerostatic coefficients and aerodynamic derivatives of rectangular cylinders measured from experiments, the effects of the Karman vortex on the bluff body aerodynamics, especially paying attention to the galloping instability, are investigated. For mitigation of Karman vortex, a splitter plate with suitable size was installed in a wake center. By the installation of a splitter plate, the sharp peak in C D -B/D (B: along-wind length, D: cross-flow length) diagrams of stationary drag force was completely disappeared. Also, the value of dC L /dα(0°) was significantly sensitive to the Karman vortex, in particular, even its sign was changed in the range of B/D=0.6 to B/D=0.7 and B/D=3.0 to B/D=4.0, which means the marked role of the Karman vortex on the galloping instability based upon the quasi-steady theory. Furthermore, the flutter derivatives were also drastically affected by Karman vortex in the rather wide range of reduced velocity. In summary, it is considered that the substantial bluff body flow, which is not affected by Karman vortex, can be characterized by the side ratio of cylinders, and the interference of the Karman vortex on the fundamental flow depends on the side ratios of cylinders.