In this paper, the 3DQ27 model of Lattice Boltzmann Method (LBM) is employed to simulate the fully-developed fluid flow and heat transfer in a curved square duct with curvature ratio (0.02–0.5) and Dean Number (0 – 200). The Dean instability in the curved square duct is fully investigated and a stability diagram is obtained with the parameters of curvature ratio and Dean number. It is found that for the square duct with high curvature ratio (i.e. curvature ratio is greater than 0.2) the onset of transition from single vortex pair to double vortex pairs depends on the Dean number and curvature ratio, while at the small curvature (i.e. curvature ratio is smaller than 0.1) the onset can be characterized by the Dean number alone. This is consistent with the results obtained from the conventional Computational Fluid Dynamic (CFD) method and experimental data. For the friction coefficient and Nusselt number, which are the functions of Dean number and curvature ratio, it was found that the present numerical results are in good agreement with the available experimental data and conventional CFD results within the given parameters range in this paper.

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