Structure of Turbulent Heat Transfer in a Separated and Reattached Flow

本研究的目的是研究二维气流在有限厚度钝平板上的分离、再连接和再发展区域的湍流换热机制。为了准确地阐明传热行为与流动行为之间的关系，在同一板上进行了传热和流动的测量。所得的要点总结如下。换热系数最大位于8.2H（H为半板厚），平均再附着点为9.6H，确定为50%逆流率点。也就是说，最大换热点存在于流动再附着的下游。在换热系数最大时，回流速率仅为15%，壁面附近的温度波动强度和雷诺数应力相对于再附着点较高。在分离泡中，最大温度波动的位置与最大速度波动的位置不同，位于分离剪切层的外侧区域。温度波动的积分时间尺度在分离泡分界附近达到最大值，在温度波动强度最大的点附近达到最小值。另一方面，在再发育流的整个区域内，它没有表现出本质的变化。功率谱和概率密度函数的特征在很大程度上取决于流区分离、再连接和再发展等流特征。在再附着流区，由于分离泡的大规模涡流脱落，功率谱存在一个宽的驼峰。此外，基于偏度和平整度因子的结果，流动的分离和再附着对温度波动统计特征的影响延伸到下游。发现再附流区附近的温度波动与低频扑动速度波动之间的相关性非常弱，并使用三线探针测量了湍流热流的两个分量。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