Single-freedom vortex-induced vibration and collision of two side-by-side circular cylinders subjected to power-law flow

The vortex-induced vibration of two side-by-side circular cylinders subjected to power-law flow is numerically investigated in a reduced velocity range of 2-10 with a fixed Reynolds number (Re = 100) at the inlet. The initial gap ratio (G/D) between the two cylinders varies from 1.5 to 3.5 with an increment of 0.5. Three power-law indices (n = 0.9, 1.0, and 1.3) are considered to cover the shear-thinning fluid (n < 1), Newtonian fluid (n = 1), and shear-thickening fluid (n > 1). Ten wake regimes are recognized in the considered cases. The boundary layer development is sensitive to both n and vibration amplitude, presenting two patterns. Collision emerges when G/D = 1.5. According to the phase difference between the cylinders' motion, two collision modes are identified, including the head-on collision and overtaking collision. Additionally, intermittent or continuous contact occurs during the collision. The lift coefficients (CL) depend on the contact pattern, presenting greater values in the case of continuous contact. In contrast, the drag coefficients (CD) are affected by n and wake regime. With the increase in n, the time-averaged drag coefficients increase, accompanied by the broadened reduced velocity range corresponding to the high values.