Flow transitions and vortical developments during vortex-ring collisions with a sharp water–oil density interface are studied using planar laser-induced fluorescence and time-resolved particle-image velocimetry techniques. Circular vortex-rings at Reynolds numbers of $$\hbox {Re}=1000, 2000$$ Re = 1000 , 2000 and 4000 colliding with a density interface characterized by an Atwood number of approximately $$A=0.045$$ A = 0.045 were investigated. Results show that at $$\hbox {Re}=1000$$ Re = 1000 , collision with the density interface produces vortical structures and flow transitions that are relatively similar to those for a solid-boundary collision. However, the dynamics underlying the present vortical formations and behaviour are different from those associated with solid-boundary collisions, in that the former are driven by baroclinic vorticity generation. Flow behaviour at $$\hbox {Re}=2000$$ Re = 2000 shows more significant deformation of the density interface by the vortex-ring but overall behaviour remains comparable. Last but not least, at $$\hbox {Re}=4000$$ Re = 4000 , the largest Reynolds number investigated here, the vortex-ring penetrates the density interface almost completely. However, buoyancy effects eventually limit its penetration and reverse its translational direction, such that it crosses back into the oil layer again with its vortex core rotational senses reversed as well. At the same time, vortex-ring fluid is shed and a significant trailing-jet is left in the former’s wake. Graphic abstract

中文翻译：

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涡环和密度界面之间碰撞中的流动转变

使用平面激光诱导荧光和时间分辨粒子图像测速技术研究涡环碰撞与尖锐的水-油密度界面期间的流动转变和涡旋发展。雷诺数为 $$\hbox {Re}=1000、2000$$ Re = 1000、2000 和 4000 的圆形涡环与密度界面碰撞，该界面的特征在于阿特伍德数约为 $$A=0.045$$A = 0.045被调查。结果表明，在 $$\hbox {Re}=1000$$ Re = 1000 处，与密度界面的碰撞产生与固体边界碰撞相对相似的涡旋结构和流动转变。然而，当前涡旋形成和行为背后的动力学与固体边界碰撞相关的动力学不同，因为前者是由斜压涡度产生驱动的。$$\hbox {Re}=2000$$ Re = 2000 处的流动行为显示了涡环对密度界面的更显着变形，但整体行为仍然具有可比性。最后但并非最不重要的是，在 $$\hbox {Re}=4000$$ Re = 4000 处，这里研究的最大雷诺数，涡环几乎完全穿透密度界面。然而，浮力效应最终会限制其穿透并反转其平移方向，使其再次穿越回油层，其涡核旋转方向也反转。同时，涡环流体脱落，在前者的尾流中留下显着的尾流。图形摘要 $$\hbox {Re}=2000$$ Re = 2000 处的流动行为显示了涡环对密度界面的更显着变形，但整体行为仍然具有可比性。最后但并非最不重要的是，在 $$\hbox {Re}=4000$$ Re = 4000 处，这里研究的最大雷诺数，涡环几乎完全穿透密度界面。然而，浮力效应最终会限制其穿透并反转其平移方向，使其再次穿越回油层，其涡核旋转方向也反转。同时，涡环流体脱落，在前者的尾流中留下显着的尾流。图形摘要 $$\hbox {Re}=2000$$ Re = 2000 处的流动行为显示了涡环对密度界面的更显着变形，但整体行为仍然具有可比性。最后但并非最不重要的是，在 $$\hbox {Re}=4000$$ Re = 4000 处，这里研究的最大雷诺数，涡环几乎完全穿透密度界面。然而，浮力效应最终会限制其穿透并反转其平移方向，使其再次穿越回油层，其涡核旋转方向也反转。同时，涡环流体脱落，在前者的尾流中留下显着的尾流。图形摘要 涡环几乎完全穿透密度界面。然而，浮力效应最终会限制其穿透并反转其平移方向，使其再次穿越回油层，其涡核旋转方向也反转。同时，涡环流体脱落，在前者的尾流中留下显着的尾流。图形摘要 涡环几乎完全穿透密度界面。然而，浮力效应最终会限制其穿透并反转其平移方向，使其再次穿越回油层，其涡核旋转方向也反转。同时，涡环流体脱落，在前者的尾流中留下显着的尾流。图形摘要