Search

We study the magnetohydrodynamic flow around a circular cylinder confined in a rectangular duct. In this configuration, both the circular cylinder and the walls of the rectangular duct are electrically insulating, while the magnetic field aligns with the axial direction of the cylinder. The experimental measurements are performed by controlling two parameters Re and N (N is the ratio of electromagnetic forces to inertial forces) in the ranges of (180–722) and (0.8–264), respectively. Utilizing the electrical potential method, we employ both movable and wall probes to obtain the local flow velocities in the wake of the cylinder. By analyzing the space correlation of the signals obtained from the wall probes, a distinct transition in the flow behavior is observed, transitioning from a three-dimensional state to a quasi-two-dimensional (Q2D) state when the external magnetic field reaches a sufficient strength (N > 3). Additionally, the Q2D state allows for a further subdivision based on the scaling relationship R e / H a ∼ (0.41 – 0.42) in the stability map, thereby distinguishing between steady and unsteady flow states, which is consistent with findings from previous studies. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Experimental and numerical investigations are conducted in order to understand the flow around identical tandem circular cylinders confined in a duct (blockage ratio b = 0.1 and aspect ratio a = 5). In this work, the Reynolds number Re ranges from 40 to 200 and the spacing ratio (distance between two centers of tandem circular cylinders to diameter, L/d) from 0 to 8. When fluid flows around a single cylinder placed symmetrically in the duct (L / d = 0), it is found that the Strouhal numbers St and mean drag coefficients C d ¯ increase with the increase in Re, although the separation angle θs decreases. For the flows around two tandem circular cylinders, the research is focused on examining the coupling effect of Re and L/d on St, flow structures, θs, C d ¯ and reverse region length Lr. Based on numerical results, the mathematical descriptions are established, C d ¯ ∼ R e − 1 , θ s ∼ R e − 1 / 2 , and S t ∼ R e − 1 . The dependence of flow structures, drag forces, θs and Lr, on L/d is described in detail with the help of approaching velocity profiles, pressure coefficient Cp, and vorticity ω z * distribution on a cylinder's surface. Through numerical simulations, the detailed mechanisms about influences of these factors on the flow properties are revealed. The experimental results evidence the occurrence of three flow modes, i.e., no vortex shedding mode, single body mode, and reattachment mode, which are determined practically by the Reynolds number and space ratio. Both the measured St based on the dominate frequencies of vortex shedding and the visual flow field match well with numerical simulations. [ABSTRACT FROM AUTHOR]