Flow-induced vibrations of three circular cylinders in an equilateral triangular arrangement subjected to cross-flow

Vortex-induced vibration of three circular cylinders (each of diameter D) in an equilateral triangular arrangement is investigated using the immersed boundary method. The cylinders, with one placed upstream and the other two side-by-side downstream, are free to vibrate in the cross-flow direction. The cylinder center-to-center spacing L is adopted as L/D = 2.0. Other parameters include the Reynolds number Re = 100, mass ratio m^* = 2.0, reduced velocity U_r = 2 ~ 15 and damping ratio = 0. Cylinder vibration responses are dependent on U_r and classified into five regimes, i.e. Regime I (U_r ≤ 3.2), Regime II (3.2 < U_r ≤ 5.0), Regime III (5.0 < U_r ≤ 6.4), Regime IV (6.4 < U_r ≤ 9.2) and Regime V (U_r > 9.2). Different facets of vibration amplitude, hydrodynamic forces, wake patterns and displacement spectra are extracted and presented in detail for each regime.