Flow-induced streamwise oscillation of two tandem square cylinders has been studied by means of free-oscillation testing in a wind tunnel. One cylinder was elastically supported so as to allow it to move in the streamwise direction; the other was fixed to the tunnel sidewalls. Small values of the reduced mass-damping parameter (Cn ≤ 1.63) have been considered. When the upstream cylinder is free to oscillate, there are two excitation regions: the first for reduced velocity, Vr, in the range 2.5 ≤ Vr ≤ 5 and cylinder gap distance to reference-length ratio, s, between 0.3 and 2, is due to movement-induced excitation accompanied by symmetrical vortex shedding, while the second, for 0.75 ≤ s ≤ 1.5 and 4.5 ≤ Vr ≤ 6.5, is due to vortex excitation by alternate Karman vortex shedding, accompanied with unstable limit-cycle oscillation. For wide gap distances over 2.5, an excitation region of the upstream cylinder occurs for 3.5 ≤ Vr ≤ 4.7, which is due to alternate Karman vortex shedding, and resembles the streamwise oscillation of a single cylinder. On the other hand, when the downstream cylinder is free to oscillate for narrow gap distances of 0.3 ≤ s ≤ 0.75, the response characteristics have an excitation region due to alternate Karman vortex shedding from the two cylinders, connected by dead water region between them, for 3.2 ≤ Vr ≤ 5.4. When s is greater than 1, the downstream cylinder experiences buffeting by wake fluctuation of the upstream cylinder.
Distribution of fluid flow pressure through tandem square cylinders with the addition of triangular cylinder as a disturbance object
