Experimental investigation of the effects of background system rotation on the flow dynamics of circular vortex rings and non-circular vortex loops

在他的博士学位中，Marcel Salmon先生将在旋转流体流动领域进行一项实验研究项目。特别是，该项目将研究涡环在背景系统旋转下的动力学和稳定性。漩涡通常被称为流体运动的“筋骨和肌肉”。它们的动力学影响到自然界和技术中涉及液体和气体运动的所有过程的绝大多数。例如，工业生产过程中的液体混合过程、汽车或飞机周围的流动中遇到的漩涡、天气现象或全球范围的海洋环流。背景系统的旋转会产生科里奥利力。众所周知，与相应的非旋转流动当量相比，这些力会从根本上改变流体流动的动力学。科里奥利力导致了许多在非旋转流动中不存在的现象，这些现象往往与直觉相反。在已发表的文献中，关于背景系统旋转对旋转流体中涡环的动力学和稳定性的影响的结果非常有限。从我们以前的研究中，我们已经知道科里奥利力在涡环上起着不稳定的作用，并且它们导致了几种二次流结构。有待确定的是究竟是什么导致了失稳，并研究了二次流结构如何依赖于独立的系统参数。也就是说，流动如何依赖于系统的旋转速度和涡环的生成参数。在萨蒙先生的研究中，涡环将在安装在我们独特的大型旋转转台设施上的大型水箱(直径1米，高度2米)内产生。当水从完全由计算机控制的涡流发生器(喷嘴-活塞布置)喷出时，环就形成了。萨蒙先生将使用我们的仪器进行和分析深入的粒子图像测速(PIV)测量。PIV是领先的、基于激光的技术，用于测量流体流动中的速度。涡环将从淹没在水箱内部水中的圆形涡流发生器喷嘴中喷射出来。喷嘴安装在旋转轴上，涡环将被弹出，以便它们在水箱内沿旋转轴向下传播。马塞尔将研究行进涡环内部和周围的流场。这些数据将与非旋转流体中的环的结果进行比较。这些比较将涉及马塞尔自己对非旋转流动的测量数据和关于非旋转系统中环的文献数据。非旋转系统中涡环的基准数据在相关的科学和工程期刊中非常丰富。根据研究的进展，该项目还旨在开始研究旋转和非旋转流动中非圆形涡环的动力学方面。对于这种非圆形涡环的动力学问题，目前基本上还没有研究。之所以如此，是因为直到最近，制造复杂的非圆形发电机喷嘴是非常困难的，例如，这种喷嘴可以在喷射的涡流结构上叠加波纹。然而，添加剂制造的最新进展现在使生产这种喷嘴结构变得容易。因此，制造这样的喷嘴进行第一次实验代表了一个极具吸引力的新研究方向，有可能揭示迄今完全未知的基本新流动现象。

For his PhD Mr Marcel Salmon will be conducting an experimental research project in the area of rotating fluid flows. In particular, the project will investigate aspects of the dynamics and the stability of vortex rings subject to background system rotation. Vortices are often referred to as the 'sinews and muscles' of fluid motion. Their dynamics affect the vast majority of all processes in nature and technology that involve liquids and gases in motion. Examples include, for instance, liquid-mixing processes in industrial production processes, vortices encountered in flow around cars or aeroplanes, weather phenomena or ocean circulation of global scale. Background system rotation induces Coriolis forces. These forces are well known to fundamentally alter the dynamics of fluid flows in comparison to the corresponding, non-rotating flow equivalent. Coriolis forces result in many, often counter-intuitive, phenomena absent in non-rotating flows. In the published literature there only exists a very limited number of results on the effects that background system rotation has on the dynamics and the stability of vortex rings in a rotating fluid. From our previous research, we already know that Coriolis forces act destabilizing on vortex rings and that they induce several secondary flow structures. What remains to be established is what exactly causes the destabilization and to investigate how the secondary flow structures depend on the independent system parameters. That is, how the flow depends on the rotational velocity of the system and the generation parameters of the vortex rings. For Mr Salmon's study vortex rings will be generated inside a large water-filled tank (diameter 1m, height 2m) mounted on our unique large-scale rotating-turntable facility. The rings form when water is ejected from a fully computer-controlled vortex-generator, a nozzle-piston arrangement. Mr Salmon will use our rig to conduct and analyse in-depth Particle-Image-Velocimetry (PIV) measurements. PIV is the leading, laser-based technology to perform velocity measurements in fluid flows. The vortex rings will be ejected from the circular vortex generator nozzle which is submerged in the water inside the tank. The nozzle is mounted on the axis of rotation and the vortex rings will be ejected such that they propagate downwards within the tank and along the rotational axis. Marcel will study the flow field within and surrounding the travelling vortex rings. The data will be compared to results for rings in non-rotating fluids. These comparisons will involve data from Marcel's own measurements for non-rotating flow and literature data for rings in non-rotating systems. Benchmark data for vortex rings in non-rotating systems are abundant in the relevant scientific and engineering journals. Depending on the progress of the research the project also aims to begin investigating aspects of the dynamics of non-circular vortex loops, in rotating and non-rotating flow. There exists essentially no research on the dynamics of such non-circular vortex loops. That is so, because until recently, it was very difficult to manufacture complex, non-circular generator nozzles which, for instance, enable one to superpose wavy undulations on the ejected vortex structure. However, the recent advances in additive manufacturing now enable producing such nozzle structures easily. Therefore, producing such nozzles to perform first experiments with them represents a highly attractive new research direction that has the potential to uncover hitherto entirely unknown, fundamental, new flow phenomena.