Experiments on vortex breakdown in a confined flow generated by a rotating disc
Experiments on vortex breakdown in a confined flow generated by a rotating disc
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DOI：
10.1017/s0022112098002092
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发表时间：
1998-09
影响因子：
3.7
通讯作者：
A. Spohn;M. Mory;E. Hopfinger
中科院分区：
文献类型：
--
作者：
A. Spohn;M. Mory;E. Hopfinger
实验研究了密闭圆柱形容器内底部旋转产生的稳态流动及其产生的涡击穿气泡。通过比较两种不同几何形状的容器内的流动，一种是刚性盖，另一种是自由表面，我们研究了破裂气泡的形成和结构依赖于周围流动的方式。通过电解沉淀技术对流动的细节进行了可视化，同时采用颗粒跟踪技术对整个流场进行了表征。我们发现，容器内的破裂气泡在许多方面与涡流管中的破裂气泡相似。首先，气泡是向内和向外开放的；其次，它们的结构就像管道流动中的涡流破裂一样，在气泡的上游具有高度的轴对称，而在气泡的后侧具有高度的不对称。然而，令人惊讶的是，我们观察到气泡同时是开放的和静止的。这表明，开放的击穿气泡不一定是循环区周期性振荡的结果。发现流动结构的不对称与容器壁面存在不对称流动分离有关。当旋转底部角速度增大时，两种构型下击穿气泡的演变是不同的：刚性盖情况下击穿气泡消失，而自由表面情况下击穿气泡持续存在。
The steady-state flow generated by a rotating bottom in a closed cylindrical container and the resulting vortex breakdown bubbles have been studied experimentally. By comparing the flow inside two different container geometries, one with a rigid cover and the other with a free surface, we examined the way in which the formation and structure of the breakdown bubbles depend on the surrounding flow. Details of the flow were visualized by means of the electrolytic precipitation technique, whereas a particle tracking technique was used to characterize the whole flow field. We found that the breakdown bubbles inside the container flow are in many ways similar to those in vortex tubes. First, the bubbles are open with in- and outflow and second, their structure is, like in the case of vortex breakdown in pipe flows, highly axisymmetric on the upstream side of the bubble and asymmetric on their rear side. However, and surprisingly, we observed bubbles which are open and stationary at the same time. This shows that open breakdown bubbles are not necessarily the result of periodic oscillations of the recirculation zone. The asymmetry of the flow structure is found to be related to the existence of asymmetric flow separations on the container wall. If the angular velocity of the rotating bottom is increased the evolution of the breakdown bubbles is different in both configurations: in the rigid cover case the breakdown bubbles disappear but persist in the free surface case.