Structure of Turbulent Heat Transfer in a Separated and Reattched Flow

分离流和再连接流中的湍流传热结构

基本信息

批准号：
63460094
负责人：
OTA Terukazu
金额：
$ 2.82万
依托单位：
Tohoku University
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (B)
财政年份：
1988
资助国家：
日本
起止时间：
1988 至 1989
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-63460094/
关键词：
Convective Heat Transfer Turbulent Flow Separated Flow Reattached Flow Boundary Layer Heat Exchanger

项目摘要

Prediction of turbulent heat transfer in the separated, reattached, and redeveloped regions is very important in relation to many types of heat exchangers. It has been clarified by numerous previous studies that the heat transfer coefficient reaches a maximum in the reattachment flow region.Furthermore, recent works have shown that the point of maximum heat transfer coefficient is, in general, different from the time-mean reattachment point, and it locates slightly upstream of the reattachment one. However, in the most of these previous studies, two different test surfaces were used. The flow in the separated and reattached regions and in the turbulent boundary layer downstream of the reattachment point is extremely complicated, and its detailed flow structure, especially concerning the characteristics of turbulent temperature fluctuation; has not been clarified.The purpose of the present study was to investigate the turbulent heat transfer mechanism in the separated, reattached, and r … More edeveloped 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 7.8H ( H being half the plate thickness ) and the mean reattachment point is 9.7H, 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 maximum temperature fluctuations is different from that of maximum velocity fluctuation and is situated in the outer region of the separated shear layer.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. Less

与许多类型的热交换器有关的分离，到达和重建区域中湍流传热的预测非常重要。以前的许多研究已经阐明了传热系数在保留流动区域中达到最大值。Furthermore最近的作品表明，最大热传递系数的点通常与时间均值的保留点不同，并且它位于重新调理的上游略有上游。但是，在以前的大多数研究中，都使用了两个不同的测试表面。分离和保留区域以及保留点下游的湍流边界层中的流动非常复杂，其详细的流动结构，尤其是关于湍流温度波动的特征；本研究的目的尚未得到澄清。研究分离，重新连接和R的湍流传热机理……在钝厚的钝平板上，二维气流的更具增长的区域具有有限的厚度。使用相同的板进行传热和流动的测量，以精确阐明传热行为与流动行为之间的相关性。所获得的要点总结如下。最大传热系数定位为7.8h（h是板厚度的一半），平均保留点为9.7h，确定为50％反向流速的点。也就是说，最大传热点存在于流动率的下游。在最大传热系数的点，与保留点相比，壁的反向流量仅为15％，温度波动的强度和雷诺在壁附近的压力相对较高。在分离气泡的位置，最大温度波动的位置与最大速度的最大速度范围位于距离的最大速度范围内。在分离气泡和最小温度波动强度附近的最小值中。另一方面，它在重新定义流动的整个区域中并未显示出必不可少的变化。功率谱和概率密度函数的特性在很大程度上取决于流动特征，例如分离，缩短，缩放和重新定义流动区域。在解剖的流动区域中，由于分离气泡中大规模涡流散发出大规模涡流，因此存在广泛的功率谱。此外，根据偏度和平坦因子的结果，流动的分离和保留对温度波动的统计特征的影响远在下游。较少的