This work presents a numerical study on vortex-induced vibration of four circular cylinders with one and two degrees of freedom subjected to uniform free-stream velocity 𝑈 at 𝛼=0°and 𝛼=45°angle of incidence, Reynolds number of 𝑅𝑒=𝑈𝐷/𝜈=150, center-to-center cylinders distance of 𝐿=3.5𝐷 and a mass ratio of 𝜌𝑐/𝜌=2.5𝑎𝑛𝑑24/𝜋. The structural damping is set to zero for reduced velocity 𝑈𝑅=𝑈/(𝑓𝑛𝐷) from 1 to 14. The high-precision code Incompact3d coupled to a moving immersed boundary method is applied to solve the governing equations. The oscillation amplitudes (𝐴𝑥, 𝐴𝑦), transverse force frequency ratio 𝑓/𝑓𝑛, wake Strouhal number 𝑆𝑡, vorticity fields, and force coefficients statistics are investigated. A wake-stiffness is inferred by 𝑓/𝑓𝑛=2 of the lateral cylinders in the 45°rotated configuration. For the one degree of freedom case, when 𝛼 changes from 0°to 45°, the overall peaks of the force coefficients statistics and oscillation amplitudes increase. In contrast, for the two degrees of freedom case (2dof), only the |𝐶¯𝐿| and 𝐶𝐿′ overall peaks increase about 10%, and the 𝐴𝑥 peak decreases around 37%. Besides, when 𝐿/𝐷 is reduced from 5 to 3.5 in 2dof, the overall maximum 𝐴𝑦 is slightly affected. However, for 𝛼=0°, the |𝐶¯𝐿| , 𝐶𝐷′ and 𝐴𝑥 peaks respectively are 106%, 284% and 177% higher at 𝐿/𝐷=3.5. For 𝛼=45°, the 𝐶𝐷′ and 𝐴𝑥 peaks increase 42% and 33%, respectively.
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