Structure of Turbulent Heat Transfer in a Separated and Reattached Flow

本文研究了有限厚度钝平板上二维气流分离区、再附着区和再发展区的湍流换热机理。为了更准确地阐明传热特性与流动特性之间的关系，在同一块平板上进行了传热和流动的测量。得到的主要结论如下：最大换热系数位于8.2H（H为半板厚）处，平均再附着点为9.6H，确定为50%反向流速点。也就是说，最大传热点存在于流动再附着的下游。在最大换热系数点处，回流率仅为15%，壁面附近的温度脉动强度和雷诺应力相对高于再附着点处。 ...更多信息 最大温度脉动与最大速度脉动不同，位于分离剪切层的外侧，温度脉动的积分时间尺度在分离气泡内的分界边界附近达到最大值，在最大温度脉动强度点附近达到最小值。另一方面，在整个再发展流区，功率谱和概率密度函数的特征并没有发生本质的变化，而与流场的分离区、再附着区和再发展区等特征密切相关。在再附着流区，由于分离泡的大尺度涡脱落，使功率谱出现一个较宽的峰。此外，基于偏斜度和平坦度因子的结果，分离和再附对温度脉动统计特征的影响远至下游，再附区附近的温度脉动与低频拍动速度脉动的相关性很弱，用双通道测量了湍流热流的两个分量一个三线探针少

The purpose of the present study was to investigate the turbulent heat transfer mechanism in the separated, reattached, and redeveloped regions of two-dimensional air flow over a blunt flat plate with finite thickness. Measurements of heat transfer and flow were conducted using the same plate in order to clarified exactly the correlation between the heat transfer behaviors and the flow ones. The main points obtained are summarized as follows.The maximum heat transfer coefficient locates at 8.2H( H being half plate thickness ) and the mean reattached point is 9.6H, which was determined as a point of 50% reverse flow rate. That is, the maximum heat transfer point exists somewhat downstream of the flow reattachment. At the point of maximum heat transfer coefficient, the reverse flow rate is only 15% and the temperature fluctuating intensity and the Reynolds stress near the wall are relatively higher compared to those at the reattachment point.In the separation bubble, the location of the … More maximum temperature fluctuations in different from that of maximum velocity fluctuation and is situated in the outer region of the separated shear layr.The integral time scale of the temperature fluctuation attains maximum near the dividing boundary in the separation bubble and minimum near the point of the maximum temperature fluctuation intensity. On the other hand, it does not show essential change in the whole region of the redeveloped flow.The characteristics of the power spectra and probability density function depend strongly upon the flow feature, such as separated, reattached, and redeveloped flow regions. In the reattached flow region, there exists a broad hump of the power spectrum due to the shedding of large-scale eddies from the separation bubble. Furthermore, based on the results of the skewness and the flatness factors, the effect of the separation and reattachment of the flow upon the statistical features of the temperature fluctuation extends far downstream.The correlation between the temperature fluctuation near the reattachment flow region and the velocity fluctuation of the low frequency flapping motion is found to be very weak and two components of the turbulent heat flux were measured using a triple wire probe. Less