Experimental investigation of vortex ring formation as a consequence of spiral vortex re-connection
Experimental investigation of vortex ring formation as a consequence of spiral vortex re-connection
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螺旋涡重连接导致涡环形成的实验研究
DOI：
10.1088/1755-1315/405/1/012033
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发表时间：
2019
期刊：
影响因子：
--
通讯作者：
O. Urban
中科院分区：
文献类型：
--
作者：
D. Štefan;P. Rudolf;M. Hudec;V. Uruba;P. Procházka;O. Urban
实验研究了空泡螺旋涡的非定常形状变化，指出了涡环（或涡圈）的重复产生。为了产生螺旋涡结构，采用了一种新设计的涡流发生器。该发生器用于研究减速旋转流导致的螺旋涡的形成，作为螺旋涡破裂的结果，这被认为是在部分负荷条件下运行的弗朗西斯涡轮机尾水管中出现相干涡带结构的主要触发机制。由于其设计，涡流发生器能够改变所产生的涡流的轴向动量通量和切向动量矩之间的比率。使用这种设置，涡流结构的行为以与弗朗西斯涡轮机的尾水管中的流速变化类似的方式变化。在一定的流动条件下，螺旋涡运动的特点是突然的螺旋纠缠，导致断开的涡环和随后的螺旋重联。由于旋流发生器装置的透明扩散器，空化涡的高速摄像机记录和无空化条件下的速度场的PIV测量都被采用。本文的主要目的是将上述涡动力学的视觉观察与在一个纵向平面和一个横截面上测量的速度场联系起来。
The unsteady shape variation of a cavitating spiral vortex is experimentally studied pointing out the repetitive creation of vortex ring (or vortex loop). To generate the spiral vortex structure, a newly designed vortex generator is employed. This generator is used to study the decelerated swirling flow leading to the spiral vortex formation as a consequence of spiral vortex breakdown, which is considered to be the main triggering mechanism for the occurrence of the coherent vortex rope structure in the Francis turbine draft tube operated at part load conditions. Thanks to its design, the vortex generator enables to change the ratio between fluxes of axial momentum and tangential moment of momentum of generated swirl. Using this set-up, the behavior of the vortex structure changes in a similar way as the flow rate variation in the draft tube of Francis turbine. At certain flow conditions, the spiral vortex movement is characterized by sudden spiral entanglement leading to disconnection of a vortex ring and followed by spiral reconnection. Thanks to the transparent diffuser of the swirl generator apparatus, both high-speed camera recording of the cavitating vortex and PIV measurements of velocity fields at cavitationfree conditions are employed. The main aim of this paper is to link the visual observation of the above described vortex dynamics with the velocity fields measured in one longitudinal and one cross-sectional planes.