Flow characteristics of two in-phase oscillating cylinders in side-by-side arrangement

Numerical simulations of flow past two side-by-side arranged cylinders with the same diameters of D, forced to oscillate transversely in a uniform cross-flow, are presented for a fixed Reynolds number of 100. The two-dimensional incompressible Navier–Stokes equations in Arbitrary-Lagrangian–Eulerian formulation are solved by Characteristic-Based-Split finite element method using MINI triangular element. The simulations are performed for four center-to-center cylinder spacings, s, ranging from 1.2D to 4.0D, corresponding to four kinds of wake pattern for the stationary two cylinders. The cylinders are oscillated in in-phase mode and their harmonic motions are restricted to relatively smaller amplitude with wide range of frequencies. The numerical results show that there exist five different flow response states, according to the different characteristics shown by the power spectra of lift forces, phase portraits of lift force against cylinder motion, time histories of energy transferring and flow fields visualized in vorticity contours. The force characteristics are also investigated in terms of time-averaged and root-mean-square quantities, and show that the roles of the gap spacing, flow response state and excitation frequency are different for different aerodynamic force quantities.