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波形壁面与空间温度调制波数匹配对Rayleigh-Bénard传热增强机制的研究

STUDY ON THE HEAT TRANSFER ENHANCEMENT MECHANISM OF RAYLEIGH-BÉNARD CONVECTION WITH WAVENUMBER MATCHING BETWEEN WAVY WALLS AND SPATIAL TEMPERATURE MODULATION

  • 摘要: 热对流广泛存在于自然现象与工程应用中, Rayleigh-Bénard(RB)对流是研究其流动与传热机制的经典模型. 当前, 针对仅含复杂几何边界或仅含非均匀加热条件的 RB 对流研究已较为充分. 然而, 对波形壁面与空间温度调制耦合下的流动与传热问题, 相关认识仍显不足. 为此, 本文采用有限差分法进行直接数值模拟, 并引入浸没边界法刻画波形粗糙下壁面, 研究在正弦波形壁面与周期性非均匀加热协同作用下, RB对流的传热特性与流场演化机理. 结果表明空间温度调制通过调控热羽流的激发位置与分布来影响传热. 当调制波数 k_\theta 与粗糙元波数 k_ob 匹配时, 温度峰值位于波峰, 热羽流高效汇入大尺度环流, 系统传热效率达到峰值, 努塞尔数(Nu)最高可达标准RB对流的130% ~ 145%, 且此强化效果随匹配波数增加而愈加显著. 当两者波数不匹配时, 传热效率接近标准RB对流, 尤其在 k_\theta = 2k_ob 的条件下, 温度峰值位于粗糙元谷底, 热羽流受几何结构严重阻碍, 导致传热被显著抑制, 且抑制程度随波数增大而加剧. 本工作揭示了波数匹配是调控对流系统热输运效率的关键机制, 对理解与设计高效热控系统具有重要意义.

     

    Abstract: Thermal convection is ubiquitous in natural phenomena and engineering applications, with Rayleigh-Bénard (RB) convection serving as a canonical model for investigating the underlying mechanisms of fluid flow and heat transfer. While current research on RB convection under individual complex geometric boundaries or only non-uniform heating conditions is relatively mature, our understanding of flow and heat transfer problems involving the coupling of wavy walls with spatial temperature modulation remains insufficient. In this study, direct numerical simulations (DNS) are performed using the finite difference method, coupled with an immersed boundary method to accurately resolve the bottom wavy wall. We investigate the heat transfer characteristics and flow field evolution mechanisms of RB convection under the synergistic influence of a sinusoidal wavy wall and periodic non-uniform heating. The results indicate that spatial temperature modulation dictates heat transfer by regulating the initiation sites and distribution of thermal plumes. When the modulation wavenumber k_\theta matches the roughness wavenumber k_ob , such that the imposed temperature peaks coincide with the wave crests, thermal plumes are efficiently integrated into the large-scale circulation. This resonance maximizes the system's heat transfer efficiency, with the Nusselt number (Nu) reaching up to 130%-145% of that in standard RB convection; furthermore, this enhancement effect becomes more pronounced as the matched wavenumber increases. Conversely, when the wavenumbers are mismatched, the heat transfer efficiency approaches that of standard RB convection. Notably, under the condition of k_\theta = 2k_ob , where temperature peaks are located at the troughs of the roughness elements, thermal plumes are severely obstructed by the geometric structures, leading to a significant suppression of heat transfer that intensifies with higher wavenumbers. This work reveals that wavenumber matching is a critical mechanism for modulating thermal transport efficiency in convective systems, providing significant insights for the understanding and design of high-performance thermal control systems.

     

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