本文通过直接数值模拟研究了水平磁场下瑞利-贝纳德对流系统的流动传热特性,其中方腔尺寸比为1:4:1.5,瑞利数5×105 ≤ Ra ≤ 5×106、哈特曼数102 ≤ Ha ≤ 104。结果表明,浮力与洛伦兹力的竞争是调控流动结构与输运标度的核心机制。在弱磁场下,活跃的热羽流为主要传热载体,对应较薄的温度边界层和强烈的流动不稳定性,粘性耗散是能量损失的主要来源;在中等磁场条件下,流动呈现出较强的准二维特性,温度边界层有所增厚,但流动仍易失稳,粘性耗散与焦耳耗散的量级相近;而在强磁场下,流动完全转变为准二维状态,稳定保持为垂直堆叠的双涡结构,此时焦耳耗散取代粘性耗散成为主要的能量损耗机制。此外还得到了努塞尔数(Nu)和雷诺数(Re)关于瑞利数(Ra)的标度关系,验证了强磁场下由耗散主导关系推导的渐进幂律。
The direct numerical simulations have been conducted to investigate the flow and heat transfer characteristics of the Rayleigh-Bénard convection system under a horizontal magnetic field. The study is conducted in a rectangular cavity with an aspect ratio of 1:4:1.5, covering a Rayleigh number range of 5×10⁵ ≤ Ra ≤ 5×10⁶ and a Hartmann number range of 10² ≤ Ha ≤ 10⁴. The aim is to analyze the impact of the magnetic field on the flow and heat transfer characteristics. The results indicate that the competition between buoyancy and Lorentz forces is the key mechanism regulating both the flow structure and transport characteristics. Under weak magnetic fields, vigorous thermal plumes serve as the primary carriers of heat transfer, which is associated with a thin thermal boundary layer and pronounced flow instabilities, with viscous dissipation being the main source of energy loss. In moderate magnetic fields, the flow exhibits pronounced quasi-two-dimensional characteristics, and while the thermal boundary layer thickens, the flow remains susceptible to instabilities, with viscous and Joule dissipation being of comparable magnitudes. Under strong magnetic fields, the flow transitions completely to a quasi-two-dimensional state, maintaining a stable, vertically stacked double-vortex structure; at this stage, Joule dissipation supplants viscous dissipation as the dominant mechanism of energy loss. Furthermore, scaling relationships between the Nusselt number (Nu) and the Reynolds number (Re) with respect to the Rayleigh number (Ra) were obtained, thereby confirming the asymptotic power-law behavior under strong magnetic field conditions.
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