论文标题
不利压力梯度湍流边界层具有上游有利压力梯度的家族
A family of adverse pressure gradient turbulent boundary layers with upstream favorable pressure gradients
论文作者
论文摘要
通过使用可变凸曲率的天花板面板，对平板湍流边界层（TBL）进行了22个有利的不良压力梯度（FAPG）的家族。我们将FAPG定义为一系列流向压力梯度的序列。使用粒子图像速度法（PIV）研究了该构型的不良压力梯度区域。在这项工作中提出和讨论了流向均值和雷诺的压力。尽管已知有利和不良压力梯度引起了TBL的相反反应，但没有发现遵循有利压力梯度（FPG）的当前不良压力梯度（APG）“反向” FPG的效应。取而代之的是，既不观察到ZPG也不是APG TBL的复杂响应。雷诺（Reynolds）的应力显示出双峰结构，外部刻度应力以$ <〜0.2δ $沿流向方向增强，并以$ y> 〜0.2δ $削弱，其中$ y $是壁正常的坐标，$δ$，$δ$，局部边界层厚度。这些是一个新的内部层的特征，以前在颠簸/山丘流中观察到，由于压力梯度符号从有利的变为不利而形成。在更强的压力梯度案例中，统计的非典型结构和趋势更为重要，在更强的压力梯度病例中，上游FPG似乎对下游APG产生了更大的影响。当前的数据集中有22个情况，提供了在FAPG配置下ZPG TBL平衡分解的完善图片。所有情况的统计信息都包括在辅助文件部分下。
A flat plate turbulent boundary layer (TBL) is experimentally subjected to a family of 22 favorable-adverse pressure gradients (FAPGs) by using a ceiling panel of variable convex curvature. We define a FAPG as a sequence of streamwise pressure gradients in the order of favorable followed by adverse, similar to the pressure gradient sequence over the suction side of an airfoil. The adverse pressure gradient region of this configuration is studied using particle image velocimetry (PIV) in the streamwise--wall-normal plane. The streamwise mean and Reynolds stresses are presented and discussed in this work. Although favorable and adverse pressure gradients are known to evoke opposing responses from a TBL, the current adverse pressure gradient (APG) that followed a favorable pressure gradient (FPG) was not found to 'reverse' the effect of the FPG. Instead, a complex response that is neither characteristic of a ZPG nor an APG TBL was observed. The Reynolds stresses showed a bimodal structure, with the outer-scaled stresses strengthening along the streamwise direction in $y < ~ 0.2 δ$ and weakening in $y > ~ 0.2δ$, where $y$ is the wall-normal coordinate, and $δ$, the local boundary layer thickness. These were signatures of a new internal layer, previously observed in bump/hill flows, formed due to the pressure gradient sign change from favorable to adverse. The non-typical structure of and trends in the statistics were more significant in the stronger pressure gradient cases, where the stronger upstream FPG seemed to have exerted a stronger influence on the downstream APG. The current dataset with 22 cases provided a well-resolved picture of the breakdown of equilibrium of the ZPG TBL under an FAPG configuration. The statistics for all the cases are included under the ancillary file section.
