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

直接的数值方法论以及有限差方法阐明了三维不稳定的分离流动和周围的三维不稳定的分离和热传递，周围表面安装的矩形块，交错的表面安装的矩形块，向后的步骤，向后的步骤，向后的步骤，矩形的通道与突然的延伸。涡流和循环分离的流动。阐明了局部和平均传热特性，并研究了其与流动结构的相关性。2。扎根的表面安装的矩形块，围绕第一排和第二行块的流量与单个块周围的流动相似，并形成了马蹄形涡流。对于第三行块，并未形成马蹄形涡流，以= 400，但最终以RE = 500形成。温度场受到流动结构的极大影响，而在t上……更高的hird行块周围被认为与第一排和第二行块周围的块不同。在每个表面上平均和五个表面上平均的平均努塞尔特数作为雷诺数的函数。3.two维倾斜的倾斜度向下倾斜的步骤，用于所有检查的倾斜角，该流量在re≦5500处稳定，但在RE = 700处变得不稳定。在从30°到75°的α范围内，α对固定长度和最大努塞尔特数的影响在雷诺数的较宽范围内相对较小。4。矩形通道随着突然的膨胀频道的延伸比降低，频道的air aI降低，对称流量保持在较高的reynolds数量上。随着AR和RE的增加，侧壁附近到达最大努塞尔特数，尤其是在上壁。流动的三维和局部努塞尔数随RE而变得严重，从而导致通道中央区域中的coanda效应降低。Sudden-expansion channelat re = 200，流动稳定且与Z轴相称。 RE = 300时的流量是稳定的，但与Y轴不对称。最大Nusselt号码远离通道中心。流动在≧400时变得不稳定。随着RE的增加到1000，在侧壁附近的大约x/h = 30的上游区域形成纵向涡流并脱落。下一步的二维分离流和热传递围绕三个向下台阶阐明。经过仔细研究的是通道膨胀比对流量和传热特性的影响。发现ER = 1.5、2.0和3.0的流量分别在RE≧700、600和500时变得不稳定。当前时间平均的重新触及长度和ER = 2.0的中心线上的流向平均速度即使在不稳定的流量状态下也与先前的实验性速度非常吻合。纵向涡流是在两个侧壁附近形成的，并且具有大小尺寸的涡流被脱落到下游。这些漩涡在很大程度上影响了流量和传热特征。流动的复杂性随着不稳定状态的ER减少而增加。即使在36.0的较大步长比率的情况下，流动的三维性也很严重，其对传热的影响也很大，尤其是在不稳定的流量状态下。较少的