Stability effect of an axial magnetic field on fluid flow bifurcation between coaxial cylinders

摘要

Numerical simulations aim to investigate the bifurcation caused by swirling flow between two coaxial vertical cylinders, and the fluid layers produced by the thermal gradient. The stability of both bifurcation and fluid layers by an axial magnetic field is analyzed. The finite-volume method is used to solve the governing Navier-Stokes, temperature and potential equations. A conducting viscous fluid characterized by a small Prandt1 number (Pr = 0.032) is placed in the gap between two coaxial cylinders. The combination of aspect ratio, gamma = 1.5 and Reynolds number, Re = 1500 for three annular gaps (R = 0.7,0.8 and 0.9) is compared in terms of flow stability, and heat transfer rates. Without a magnetic field, the vortex breakdown takes place near the inner cylinder due to the increased pumping action of the Ekman boundary layer. Fluid layered structures are developed by the competition between buoyancy and viscous forces. The increase in the magnitude of the magnetic field retarders the onset of the oscillatory instability caused by the disappearance of the vortex breakdown and reduces the number of fluid layers. The limits in which a vortex breakdown bubble manifests and the limits of transition from the multiple fluid layers to the single fluid layer are established.