"Turbulent Transport Mechanismsof Natural Convection over Upward-Facing Horizontal, Heated plate"

本文从实验和分析两个方面研究了水平向上加热平板上的自然对流。特别关注的是湍流过渡机制和过渡区域的局部愈合转移特征。在常温下用水和恒壁面热流试验板进行了研究，为了对平板上的流动和温度场有基本的了解，用染料和液晶测温仪对平板上的流动和表面温度进行了可视化。结果表明：(1)在前缘附近，层流边界层在平板上发展；(Ii)水流在距边缘一定距离处进行三维分离。(Iii)当板足够宽时，分离后的流动无规律地波动，并且在板的中心部分实现完全湍流状态。在这些现象中，三维分离和随后的湍流转变尤为重要，因为这些区域占据了总表面积的相当大一部分。因此，接下来我们对这些现象进行了数值模拟。为此，发展了一种随时间变化的三维分析方法。结果是令人满意的。目前的分析很好地预测了流动分离的发生和随后向湍流的转变。此外，局部换热系数的计算结果与实验结果吻合较好。

Natural convection induced over the upward-facing horizontal, heated plate have been investigated both experimentally and analytically. Special concerns are directed to the turbulent transition mechanisms and the local heal transfer characteristics in the transitional region. The investigations have been carried out with water at room-temperature and with the test plate of constant wall heat flux, In order to obtain basic insight into the flow and temperature fields over the plate, the flow over the plate and the surface temperatures of the plate were visualized with dye and liquid crystal thermometry. The results showed that the following phenomena occur over the plates : (i) The laminar boundary layer flow develops over the plate in the vicinity of the leading edge. (ii) The flow separates three-dimensionally at certain distance from the edge. (iii) The separated flow, then, fluctuate irregularly and a fully turbulent state is realized in the central portion of the plate when the plate is wide enough. Among these phenomena, the three-dimensional separation and the succeeding turbulent transition are of particular importance, because these regions occupy considerable portion of the total surface area. Thus, we next carried out the numerical simulation on these phenomena. A time-dependent, three-dimensional analysis has been developed for this purpose. The results are quite satisfactory. Present analysis well predicted the occurrence of the flow separation and the succeeding transition to turbulence. Moreover, the local heat transfer coefficients are in good agreement between the analysis and experiment.