A numerical research work is carried out to examine fluid–structure interaction in flow over six inline square cylinders undergoing transverse oscillations via the lattice Boltzmann method. The impact of the oscillation frequency ratio (\(\:{f}_{e}/{f}_{o}\)), where imposed oscillation frequency is represented as \(\:{f}_{e}\) and \(\:{f}_{o\:}\)is the natural vortex shedding frequency of a stationary cylinder, on wake dynamics and flow patterns is examined. Simulations are performed at Reynolds number of Re = 80, with a non-dimensional gap spacing (s/d = 1.0) and an oscillation amplitude ratio of A/d = 0.2. The frequency ratio is varied in the range 0.1 < \(\:{f}_{e}/{f}_{o}\:\)≤ 2.0. Three distinct flow patterns are identified: synchronous lock-on (0.8 ≤ \(\:{f}_{e}/{f}_{o}\)≤ 1.4), quasi-periodic lock-on-I (1.6 ≤ \(\:{f}_{e}/{f}_{o}\) ≤ 2.0) and quasi-periodic non-lock-on-I (0.1 ≤ \(\:{f}_{e}/{f}_{o}\)≤ 0.6). The synchronization range is wider than that reported for single oscillating cylinder. A single coherent wake envelops the entire cylinder array, with wake recovery occurring at higher oscillation frequencies due to merging of vortex and formation of multi-polar vortices downstream of final cylinder. The first cylinder experiences highest mean drag, followed by a reduction and gradual increase along the downstream cylinders.
