NUMERICAL STUDY OF NATURAL CONVECTION UNDER AN IMPOSED ALTERNATING MAGNETIC FIELD IN CYLINDRICAL VESSEL

3D magneto-hydrodynamic DNS inside a cylindered vessel filled with a liquid metal under an alternating magnetic (AM) field and bounded by a vertical temperature gradient were performed. The numerical setup aims to explore a wide range of Hartman number (Ha) and shielding parameter (Sw) to interrogate the average Nusselt number and the flow patterns. When only a temperature gradient is applied to the fluid, it is well known that above a critical Rayleigh number (Ra), the fluid becomes unstable, and this situation is referred to as Rayleigh-Bénard Convection (RBC). A large amount of research has been dealing with this kind of instability to understand the flow patterns. Our study is dedicated to this configuration when an AM field is added. The vessel is placed inside an inductor supplied with an alternating electrical current. The power distribution within the conducting liquid metal is non-uniform and depends on the frequency through Sw, and the AC amplitude through Ha. Playing on both parameters, the Lorentzs force field and the Joule heating field can be controlled. The conjugation of both effects (Joule heating and Lorentz force) on the fluid motion leads to various regimes depending on Sw and Ha. In a first step RBC has been simulatedat moderate Ra. In a second step, DNS have been computed including Maxwell’s equations in the regime of low magnetic Reynolds number (Rm<<1). When Sw>=1, It has been found that the LSC is cancelled by the Lorentz force’s stirring effect and  two horizontal tori are generated in the upper half and the lower half of the vessel. The time and volume average temperatures of the tori are different, and their values depend on the intensity of Joule heating and Lorentz force. The heat and mass transfer between the tori is negligible when averaged in time, but bursts of fluid through the mid plane occur intermittently. In addition, it was observed that the AM field enhances the total heat exchange compare to classical RBC.