Three-cylinder oscillator under flow: Flow induced vibration and energy harvesting

This numerical study aims to examine the viability of energy harvesting by three rigidly coupled cylinders in an equilateral triangular pattern, as well as reveal the flow-induced vibration responses of such a system. First, a wide range of reduced velocity (U-r = 1-30) is selected to examine the effects of gap ratios (G = 0.01 to 1). Then, based on these results, various damping ratios (zeta = 0.013 - 0.7) are tested to further improve the efficiency. The results show that with a decrease in the gap, the energy converter generates a higher amplitude and a lower oscillation frequency. In the high-flow-speed region, the fully developed galloping branch can be found in G = 0.01 and 0.2. For G = 0.5, a new branch appears, in which the vortex-induced vibration and galloping vibrate in combination way and reach a stable state. The amplitude in the new branch is higher than that of the upper branch, whereas the oscillation frequency still locks into the natural frequency. Furthermore, a new vortex shedding mode of 4P can be detected in this branch. At small gaps, the harnessed power increases without an upper limit owing to the galloping. As expected, the maximum efficiency point is located on the upper branch. In terms of damping ratio variation, the three-cylinder energy converter has high sensitivity, and zeta = 0.5 is the critical damping ratio for amplitude and frequency responses. The novel energy converter exhibits potential for power collection, and G = 0.2, zeta = 0.2 respectively is the most suitable arrangement and damping parameter for energy harvesting in all tests.