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

• 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

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

在分离区、再附着区和再发展区中的湍流传热的预测对于许多类型的换热器是非常重要的。以往的研究表明，换热系数在再附着区达到最大值，而最近的研究表明，换热系数最大值点一般不同于时间平均再附着点，而是位于再附着点的上游。然而，在大多数这些先前的研究中，使用了两种不同的测试表面。分离区、再附着区和再附着点下游湍流边界层的流动是极其复杂的，其详细的流动结构，特别是湍流温度脉动特性至今还没有弄清楚。本文的目的是研究分离区、再附着区和再附着点下游湍流边界层的湍流传热机理。结果表明，分离区、再附着区和再附着点下游湍流边界层的湍流温度脉动特性与湍流边界层的温度脉动特性基本一致，而湍流边界层的温度脉动特性与湍流边界层的温度脉动特性基本一致 ...更多信息 有限厚度钝平板上二维气流的发展区域。为了更准确地揭示换热特性与流动特性之间的关系，在同一块平板上进行了换热和流动的测量，得到的主要结论是：最大换热系数位于7.8H（H为平板厚度的一半）处，平均再附着点为9.7H，该点确定为50%反向流速的点。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。最大温度脉动位置与最大速度脉动位置不同，位于分离剪切层的外侧，积分时间温度脉动尺度在分离泡的分界面附近达到最大值，在最大温度脉动强度点附近达到最小值，而在整个再发展流区温度脉动尺度并没有发生本质变化，功率谱和概率密度函数的特征与分离泡、再附着区和再发展流区等流动特征密切相关。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，基于偏度和平坦度因子的结果，分离和再附着的流动对温度波动的统计特征的影响延伸到下游。少

项目成果

太田照和、加藤弘剛: "剥離と再付着を伴う厚板からの乱流熱伝達" 日本機械学会第68期全国大会(発表予定). (1990)

Terukazu Ota、Hirotake Kato：“厚板的湍流传热与剥离和再粘合”，第 68 届日本机械工程师学会全国会议（1990 年）。

Terukazu Ota,Hirokake Kato: "Turbulent Heat Transfer in a Separated and Reattached Flow over a Blunt Flat Plate" 3rd ASMEーJSME Thermal Engineering Joint Conference(発表予定). (1991)

Terukazu Ota、Hirokake Kato：“钝平板上分离和重新附着流中的湍流传热”第 3 届 ASME-JSME 热工联合会议（即将提交）（1991 年）。

太田照和,加藤弘剛: "剥離と再付着を伴う厚板からの乱流熱伝達" 日本機械学会第68期全国大会. (1990)

Teruwa Ota、Hirotake Kato：“厚板的湍流传热与剥离和再粘合”，第 68 届日本机械工程师学会全国会议（1990 年）。

Hideya Nishiyama, Terukazu Ota and Kunihiro Sato: "" Temperature Fluctuations in a Separated and Reattached Flow over a Blunt Flat Plate "" Warme- und Stoffubertragung, Vol.23 (1988) 275-281.

Hideya Nishiyama、Terukazu Ota 和 Kunihiro Sato：“钝平板上分离流和再附着流中的温度波动”Warme- und Stoffubertragung，第 23 卷 (1988) 275-281。

Hideya,Nishiyama;Terukazu Ota;Kunihiro Sato: Warme-und Stoffubertragung. 23. 275-281 (1988)

秀也，西山；太田照和；佐藤邦宏：温暖和Stoffubertragung。