Numerical Study on the Vortex-induced Vibration Energy Harvesting Performance of Tandem Circular Cylinders with Unequal Mass Ratios

In this study, three-dimensional numerical simulations were performed on a vortex-induced vibration (VIV) energy harvesting system consisting of tandem circular cylinders. The focus is on the effects of varying the mass ratio between the upstream cylinder (UC, mUC*) and the downstream cylinder (DC, mDC*), with mDC*/mUC* = 0.75, 1.0, 1.25 and 1.5, on the vibration characteristics and energy harvesting performance of the system, while the cylinder diameter is fixed and the center-to-center distance is three times cylinder diameter. Results indicate that the value of mDC*/mUC* exerts a strong influence on the cylinder responses and wake patterns. Both cylinders exhibit ‘lock-in’ behavior, with the DC locked in at a slightly higher frequency and exhibiting broader lock-in range. The UC and DC reach peak responses at different reduced velocities, with the DC delayed in onset of VIV yet amplified in vibration amplitude. The harvested power of both cylinders increases with mUC*, with the DC outperforming the UC. When mUC* = 6, the total harvested power reaches 6.21 mW at mDC*/mUC* = 1.5, representing an increase of 35% and 56% compared to that at mDC*/mUC* = 1.25 and 1.0, respectively. At mDC*/mUC* = 1.0, increasing the mass of each cylinder enhances 8-shaped trajectory and vibration amplitude, vortex shedding while maintaining the dominant 2S vortex shedding mode. The DC exhibits reduced periodicity and a phase lag relative to the UC, though its periodicity improves slightly as mDC* increases.