An Experimental Study of Turbulent Natural Convection Boundary Layers
An Experimental Study of Turbulent Natural Convection Boundary Layers
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DOI：
10.1115/1.3580236
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发表时间：
1969-11
影响因子：
--
通讯作者：
G. Vliet;C. K. Liu
中科院分区：
文献类型：
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作者：
G. Vliet;C. K. Liu
在恒热流垂直平板上进行了带水的湍流自然对流边界层的实验研究。给出了层流、过渡和湍流自然对流的局部换热数据，重点介绍了湍流区域。对于Prandtl数的三倍范围，数据扩展到修正的瑞利数1016。结果表明，在1012<；Ra*<；1014范围内发生自然转变，即在Ra*=104时发生完全发展的湍流流动。在使用脱扣杆的情况下，后一值可低至2×1013。采用联合时间条纹标记氢气泡方法研究了湍流边界层流动的物理结构。给出了热膜传感器获得的Ra*值在8.7×1013~7.1×1014之间的温度数据和温度修正后的速度数据。在所研究的变量范围内，主要结论是：(A)局部换热系数随长度略有减小，(B)证实了过渡区涡街层衰减为纵向涡型结构，以及(C)热场和速度场的外部可以用功率分布来近似，几乎符合到目前为止的所有数据。
An experimental investigation on turbulent natural convection boundary layers has been conducted with water on a vertical plate of constant heat flux. Local heat transfer data are presented for laminar, transition, and turbulent natural convection, with the emphasis on the turbulent regime. The data extend to a modified Rayleigh number of 1016 for a threefold range in Prandtl number. The results indicate that natural transition occurs in the range 1012 < Ra* < 1014 ; i.e., fully developed turbulent flow occurs by Ra* = 104 . This latter value can be as low as 2 × 1013 with the use of a trip rod. The physical structure of the turbulent boundary-layer flow was studied using the combined time-streak marker hydrogen bubble method. Temperature data and temperature corrected velocity data obtained by hot-film sensors are presented for Ra* values between 8.7 × 1013 and 7.1 × 1014 . For the range of variables investigated, the major conclusions are (a) the local heat transfer coefficient exhibits a slight decrease with length, (b) confirmation that the vortex street layer in the transition region decays into a longitudinal-vortex-type structure, and (c) the outer portion of the thermal and velocity fields can be approximated by power profiles that fit almost all the data available to date.