Flow development over isolated droplet-inspired shapes

Zhang Xueqing; Tuna Burak A.; Yarusevych Serhiy; Peterson Sean D.

摘要

Flow development over isolated, surface-mounted, droplet-inspired three-dimensional obstacles submerged in a laminar boundary layer is investigated at a Reynolds number based on obstacle height of Re-h = 2070 using particle image velocimetry. Three geometries are considered, a sessile droplet; a droplet on the verge of runback (depinning); and a spherical cap, which serves as a first order approximation of a sessile droplet. For all three models a horseshoe vortex system forms at the leading edge and wraps around the obstacle, with the sessile model producing the most prominent horseshoe system due to its relatively high fore-body bluntness. Shear layer vortices shed from the objects form arch vortices, which produce mean streamwise vortices in wakes of the models. Downstream of the objects, turbulent fluctuations grow in a wedge shape. The spreading mechanisms in the wall-normal and lateral directions are explored through proper orthogonal decomposition of the velocity fluctuations. The analysis shows that wall-normal growth is associated with shear layer vortex breakdown, while lateral spreading is influenced by interactions between the horseshoe vortex system and streamwise wake vortices. Overall, similarity between the chopped and sessile model flow fields suggest the spherical cap is a reasonable first order approximation of a sessile droplet from a vortex dynamics perspective. Shear layer vortices shed from the runback model exhibit more complete merging than for the other two models, perhaps due to the smaller radius of curvature at the object peak. This model also exhibits a more muted horsheshoe vortex system and narrower near-field wake than the sessile model, suggesting less disruption to the incoming boundary layer flow.

机译：基于使用粒子图像速度的RE-H = 2070的障碍物高度，在雷诺数，在层压层中浸没在层边界层中的隔离，表面安装的液滴启发的三维障碍物。考虑了三个几何形状，一个柄液滴;返回边缘的液滴（拆除）;和球形帽，用作柄液滴的第一阶近似。对于所有三种模型，马蹄涡流系统形成在前缘和围绕障碍物周围的卷，其术术根据其相对较高的前体钝性产生最突出的马蹄形系统。剪切层涡流从物体形成拱形涡旋，这在模型的唤醒中产生了平均流动涡旋。在物体的下游，湍流波动以楔形生长。通过适当的速度波动的正交分解来探索壁正常和横向方向中的扩散机构。该分析表明，壁正常生长与剪切层涡流击穿有关，而横向扩散受马蹄涡流系统之间的相互作用和流动唤醒涡流的影响。总的来说，切碎和无柄模型流动场之间的相似性表明球形帽是从涡流动力学视角的合理的第一顺序近似术。从回返模型的剪切层涡流表现出比其他两个模型更完整的合并，也许是由于物体峰处的曲率半径较小。该模型还展现出更柔和的Horsheshoe Vortex系统和比无柄型模型更窄的近场尾尾，这表明对进入的边界层流量的破坏性较少。

Flow development over isolated droplet-inspired shapes

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