Three-dimensional natural convective states in a narrow-gap horizontal annulus
Three-dimensional natural convective states in a narrow-gap horizontal annulus
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DOI：
10.1017/s0022112001005067
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发表时间：
2001-10
影响因子：
3.7
通讯作者：
M. P. Dyko;K. Vafai
中科院分区：
文献类型：
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作者：
M. P. Dyko;K. Vafai
对由两个同心水平圆柱形成的窄间隙环空中的浮力驱动流动进行了数值研究。通过求解流体运动和热传导的三维瞬变方程，研究了具有不透水端壁的环空中出现的多种超临界状态，这些状态在各种应用中都会遇到。首次证明了三维超临界状态发生在窄间隙环空中，并确定了四个这样的状态的存在。这四种状态的特点是由于热不稳定而在环空上部形成的对旋辊的旋转方向和方向，并分别表现为(I)横向辊，(Ii)旋转方向相反的横向辊，(Iii)与横向辊组合的纵辊，以及(Iv)与横向辊组合的反向旋转的纵向辊。在瑞利数接近和超过临界值时进行模拟，以深入了解影响二次流结构发展的物理过程。深入研究了超临界流场和温度分布随瑞利数的变化规律以及二次流和一次流之间的相互作用。对每种超临界状态下影响辊数的因素进行了研究。换热结果以局部Nusselt数分布和整体环空Nusselt数的形式给出。文中还研究了在流场瞬变演化早期发生的二维自然对流。在较宽的环空半径比和瑞利数范围内得到的结果与前人的实验和数值研究结果吻合较好，从而验证了本数值格式的有效性。
Buoyancy-driven flow in a narrow-gap annulus formed by two concentric horizontal cylinders is investigated numerically. The three-dimensional transient equations of fluid motion and heat transfer are solved to study multiple supercritical states occurring within annuli having impermeable endwalls, which are encountered in various applications. For the first time, three-dimensional supercritical states are shown to occur in a narrow-gap annulus and the existence of four such states is established. These four states are characterized by the orientations and directions of rotation of counter-rotating rolls that form in the upper part of the annulus owing to thermal instability, and exhibit (i) transverse rolls, (ii) transverse rolls with reversed directions of rotation, (iii) longitudinal rolls in combination with transverse rolls, and (iv) longitudinal rolls with reversed directions of rotation in combination with transverse rolls, respectively. Simulations are performed at Rayleigh numbers approaching and exceeding the critical value to gain insight into the physical processes influencing development of the secondary flow structures. The evolution of the supercritical flow fields and temperature distributions with increasing Rayleigh number and the interaction between the secondary and primary flows are thoroughly investigated. Factors influencing the number of rolls are studied for each supercritical state. Heat transfer results are presented in the form of local Nusselt number distributions and overall annulus Nusselt numbers. Two-dimensional natural convection occurring early in the transient evolution of the flow field is also examined. Results obtained for a wide range of annulus radius ratios and Rayleigh numbers are shown to be in excellent agreement with results from previous experimental and numerical studies, thereby validating the present numerical scheme.