Lattice Boltzmann Method Based Simulations for Flow Arround Row of Transversely Oscillating Cylinders

ABSTRACT

This paper reports results of two-dimensional numerical simulations for flow across a row of transversely oscillating square cylinders using lattice Boltzmann method (LBM). The amplitude of oscillation is fixed at A/d = 0.2 (where A is amplitude of oscillation and d is the size of the cylinder) with forcing frequency ratio (f_e/f_o, where f_e is frequency of cylinder oscillation and f_o is frequency of vortex shedding for flow across row stationary of cylinders) varied as 0.1 ≤ f_e/f_o ≤ 1.7. The gap ratio (s/d, where s is the distance between surfaces of two adjoining cylinders) and Reynolds number (Re) are fixed at 4 and 80 respectively. Within the range of forcing frequency considered in this investigation the two flow regimes proposed are the non-lock-on regime and lock-on regime. In the non-lockon regime the cylinder oscillation frequency and vortex shedding frequency appear separately in the power spectrum of lift coefficient, however in lock-on regime the vortex shedding frequency is locked to the cylinder oscillation frequency. The onset of lock-on regime occur at f_e/f_o = 0.8 and is further continued in the entire range of forcing frequency considered in this investigation. The mean drag coefficient is found to be maximum just before the onset of lock-on regime and remains on the higher side near f_e/f_o = 1.0 and reduces latter. The root mean square lift coefficient also shoots to maximum just before the onset of lock-on regime. The flow within the non-lock-on regime is found to be quasi-periodic and within the lock-on regime it is synchronous in nature. It is interesting to note that the flow across row of stationary cylinders at Re = 80 is quasiperiodic in nature.

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