Numerical simulations of flow around dual tandem circular cylinders under a strong axial magnetic field

This work is dedicated to understand the magnetohydrodynamic (MHD) flow around two identical tandem circular cylinders confined in a duct under external axial magnetic field. The influences of magnetic field (represented by the Hartmann number Ha), inlet velocity of conducting fluid (represented by the Reynolds number Re), and the gap ratio (L/d, the ratio of the distance between the centers of two cylinders to the diameter of the circular cylinder) on the flow regimes, vortex shedding frequency, pressure coefficients, drag coefficients, and pressure drop are investigated. The simulations are conducted in the parameter ranges 2 ≤ L / d ≤ 8, 180 ≤ R e ≤ 1440, and 101 ≤ H a ≤ 1818, respectively. Four flow modes are observed, namely, no vortex shedding, single body, reattachment regime, and vortex shedding (VS) modes, with various H a / R e 2 and L/d values. For L / d > 5, the flow field presents the VS flow model, a vortex street with synchronous periodic shedding appears behind the two cylinders, and the vortex shedding frequency matches well with that of the single one. The pressure coefficient shows different tendencies because of the arrangement of two circular cylinders. It can be found that the mean drag coefficients for the upstream circular cylinder and the downstream circular cylinder vary with R e / H a 0.8. For R e = 361, H a = 504 and R e = 722, H a = 1212, the flow field remains almost unchanged, which implies the balance between inertial force and Lorentz force because the inertial force would promote the flow, while the electromagnetic force leads to the reverse effect. Furthermore, the effects of magnetic field and inlet velocity of metal fluid on pressure drop Δ P between inlet and outlet can be fitted as a linear relation Δ P ∼ ReHa.