A numerical study of quasistatic magnetoconvection ; 準靜態磁對流的數值研究 ; numerical study of quasistatic magnetoconvection ; Zhun jing tai ci dui liu de shu zhi yan jiu

M.Phil. ; Thermally driven convection has many useful applications in nature and in our daily life. Rayleigh Bénard (RB) convection, a fluid layer heated from bottom and cooled on top, is the traditional model to investigate the nature of thermally driven convection. Convection has been studied experimentally and numerically and numerical simulations of convection have become a trend recently to simulate large scale convection such as ocean convection, mantle convection and solar convection. Many studies have extended traditional RB convection by adding different forces and equations to the governing equation to understand the convection behaviour even furthur. ; In this thesis, we present a numerical study of quasistatic magnetoconvection in a cubic Rayleigh-Bénard (RB) convection cell subjected to a vertical external magnetic field. For moderate values of the Hartmann number Ha(characterising the strength of the stabilising Lorentz force), we find an enhancement of heat transport (as characterised by the Nusselt number Nu). Furthermore, a maximum heat transport enhancement is observed at certain optimal Haₒₚₜ. The enhanced heat transport may be understood as a result of the increased coherency of the thermal plumes, which are elementary heat carriers of the system. To our knowledge this is the first time that a heat transfer enhancement by the stabilising Lorentz force in quasistatic magnetoconvection has been observed. We further found that the optimal enhancement may be understood in terms of the crossing between the thermal and the momentum boundary layers (BL) and the fact that temperature fluctuations are maximum near the position where the BLs cross. These findings demonstrate that the heat transport enhancement phenomenon in the quasistatic magnetoconvection system belongs to the same universal-ity class of stabilising−destabilising (S-D) turbulent flows as the systems of confined Rayleigh-Bénard (CRB), rotating Rayleigh-Bénard (RRB) and double-diffusive convection (DDC). This is further supported by ...