Abstract: In this paper, to study the characteristics of the flow in a laminar regime, an immersed boundary-lattice Boltzmann flux solver (IB-LBFS) is applied to numerically simulate the unsteady viscous flows around two fixed and rotating circular cylinders in side-by-side arrangement. This method applies finite volume discretization to solve the macroscopic governing equations with the flow variables defined at cell centers. At the cell interface, numerical fluxes are physically evaluated by a local lattice Boltzmann solution. In addition, the no-slip boundary condition is accurately imposed by using the implicit boundary condition-enforced immersed boundary method. Due to the simplicity and high efficiency of IB-LBFS on non-uniform grids, it is suitable for simulating fluid flows with complex geometries and moving boundaries. Firstly, numerical simulations of laminar flow past two side-by-side cylinder are performed with different gap spacings at Reynolds numbers of 100 and 200. The simulation results show that a small gap spacing induces a biased flow and forms an irregular big wake behind two cylinders at a low Reynolds number. As the gap spacing increases, an in-phase or anti-phase flow is observed. Then, the effects of the main important parameters on flow characteristics are analyzed for flow past two side-by-side rotating cylinders, including the rotational speed, Reynolds number, and gap spacing. As the rotational speed is increased, the numerical results illustrate that unsteady wakes are suppressed and the flow becomes steady. As the gap spacing is increased, two separate vortex streets behind each cylinder are formed with a definite phase relationship and single shedding frequency.

Key words: Immersed boundary method (IBM); Lattice Boltzmann flux solver (LBFS); Moving boundary; Side-by-side cylinders

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