权益分类	功能权益	普通用户	{{item.name}}会员
{{category.name}}	{{benefitItem.name}}

DNS of Large Scale Vortices and Heat Transfer Mechanism in a Three-Dimensional Unsteady Separated Flow

三维非定常分离流中大尺度涡的DNS与传热机理

基本信息

批准号：
16560170
负责人：
OTA Terukazu
金额：
$ 2.24万
依托单位：
Tohoku University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2004
资助国家：
日本
起止时间：
2004 至 2005
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-16560170/
关键词：
Separated flow Reattached flow Convective heat transfer DNS Surface-mounted body Horseshoe vortex Backward-facing step Sudden expansion channel

项目摘要

Direct numerical methodology along with the finite difference method clarified the three-dimensional unsteady separated flow and heat transfer around the pair of surface-mounted rectangular blocks, the staggered surface-mounted rectangular blocks, the backward-facing steps and the rectangular channels with sudden expansion.1.Pair of surface-mounted rectangular blocksIt is found that the present numerical results well simulate the observed ones such as horseshoe vortices and the recirculating separated flow. Local and mean heat transfer characteristics are clarified and their correlations with the flow structure are investigated.2.Staggered surface-mounted rectangular blocksThe flow around the first- and second-row blocks is similar to that around the single block, and horseshoe vortices are formed. For the third-row block, a horseshoe vortex is not formed up to Re=400 but is finally formed at Re=500. The temperature field is greatly affected by the flow structure, and that around the t … More hird-row block is considerably different from those around the first- and second- row blocks. The mean Nusselt numbers averaged on each surface and also on the five surfaces are presented as a function of the Reynolds number.3.Two-dimensional inclined downward stepFor all the inclination angles examined, the flow is steady at Re≦5500 but becomes unsteady at Re=700. In a range of α from 30°to 75°, effects of α upon the reattachment length and the maximum Nusselt number are relatively small in wide range of the Reynolds number.4.Rectangular channel with sudden expansionAs the aspect ratio AR of channel decreases, the symmetric flow is maintained to higher Reynolds number. The maximum Nusselt number is reached near the side wall with increases of AR and Re, especially on the upper wall. Three-dimensionality of flow and local Nusselt number becomes severe with Re, resulting in a decrease of Coanda effect in the central region of the channel5.Sudden-expansion channelAt Re=200, the flow is steady and symmetric as to the y-and z-axes. The flow at Re=300 is steady but asymmetric as to the y-axis. The maximum Nusselt number is attained away from the channel center. The flow becomes unsteady at ≧400. As Re increases to 1000, the longitudinal vortices are formed and shed in the upstream region of about x/H=30 in the neighborhood of the side walls6.Downward stepsThree-dimensional separated flow and heat transfer around three downward steps are clarified. Minutely investigated are effects of the channel expansion ratio ER upon the flow and heat transfer characteristics. It is found the flow for ER=1.5, 2.0 and 3.0 becomes unsteady at Re≧700, 600 and 500, respectively. The present time averaged reattachment length and the streamwise mean velocity on the center line for ER=2.0 are in excellent agreement with the previous experimental ones even in the unsteady flow state. The longitudinal vortices are formed in the neighborhood of two side walls and the vortices having large and small scales are shed to the downstream. These vortices influences largely upon the flow and heat transfer features. The complexity of flow increases with a decrease of ER for the unsteady state. Even in the case of large step aspect ratio of 36.0, the three-dimensionality of the flow is severe and its effects upon the heat transfer are great, especially in the unsteady flow state. Less

采用直接数值方法沿着有限差分法，对矩形块体对、交错矩形块体对、交错后向台阶和突然膨胀的矩形通道。结果表明，本文的数值计算结果较好地模拟了马蹄涡和回流分离流等实验现象。2.错排矩形块体第一排和第二排矩形块体周围的流动与单个矩形块体周围的流动相似，并形成马蹄涡。对于第三排块体，在Re=400之前没有形成马蹄形涡，但在Re=500时最终形成。流场结构对温度场影响很大， ...更多信息第三行块与第一和第二行块周围的块有很大不同。3.二维倾斜向下台阶对于所研究的所有倾斜角，在Re = 5500时流动是稳定的，但在Re=700时变得不稳定。在30° ~ 75°的范围内，在较宽的雷诺数范围内，α对再附着长度和最大努塞尔数的影响相对较小。4.突扩矩形通道随着通道纵横比AR的减小，在较高的雷诺数下，通道内的对称流动得以维持。随着AR和Re的增加，在侧壁附近Nusselt数达到最大，尤其是在上壁。5.突扩通道在Re=200时，流场稳定，且沿y轴和z轴对称。Re=300时的流动是稳定的，但关于y轴是不对称的。最大努塞尔数是在远离通道中心的地方获得的。在400 ℃时流动变得不稳定。当Re增加到1000时，在侧壁附近x/H=30左右的上游区域形成并脱落纵向涡。6.下台阶阐明了三个下台阶周围的三维分离流动和换热。详细研究了通道膨胀比ER对流动和传热特性的影响。发现ER=1.5、2.0和3.0时的流动分别在Re = 700、600和500时变得不稳定。在非定常流动条件下，本文给出的时间平均再附着长度和中心线上的流向平均速度与前人的实验结果吻合得很好。纵向涡在两侧壁附近形成，大小尺度的涡向下游脱落。这些涡对流动和传热特性有很大的影响。对于非定常状态，流动的复杂性随着ER的减小而增加。即使在大台阶高宽比（36.0）的情况下，流动的三维性也很严重，对传热的影响很大，特别是在非定常流动状态下。少