Turbulent vortex structure of liquid metal flow in pipe subjected to fringing magnetic field

Jie Mao - Liming Xie - Kai Xiang - Hao Wang

School of Mechanical Engineering, Hangzhou Dianzi University, Hangzhou 310018, China

Abstract
Liquid metal flow in a conducting pipe subjected to a fringing magnetic field has been investigated numerically using the dynamic Smagorinsky model. The magnetic field imposed on the flow field consists of three zones: increasing magnetic-field strength from zero to a constant, constant strength, and decreasing from a constant to zero. Hartmann numbers in the constant magnetic zone vary from 85.5 to 320. Turbulence in a hydrodynamic flow (Re = 21375) is suppressed by the magnetic field after the flow enters the magnetic field zone. The normalized pressure gradient along the flow direction depends on the Hartmann number, whereas the transverse pressure difference at the cross-section along the flow direction is independent of the Hartmann number. Vortex patterns are evaluated using Q and Liutex methods. Both methods show identical vortex patterns with a range of Hartmann numbers. Under the action of a weak magnetic field, the vortex is transformed into thin and long strip structures along the flow direction. In the fringing magnetic field area, an annular vortex pattern appears with a moderate Hartmann number. The vortices are transformed into quasi-two-dimensional strips that are parallel to the external magnetic field direction. The rotation direction is opposite to an adjacent vortex. Damping of turbulence caused by the magnetic field is most substantial with decreasing magnetic field strength. The vortex pattern evolution is presented in an unabbreviated fringing magnetic field. The Liutex method can present the MHD turbulent vortex pattern more clearly without flaw. Moreover, the magnetic field can be used to control the vortex pattern in industry applications. Tables 3, Figs 13, Refs 33.