Numerical Simulation and Experimental Visualization of Vortex Breakdown: A Vortex-Line View of the Phenomenon

同时进行计算和实验研究，重点通过观察流动的涡线的运动学以及它们在构成涡核的束中的拓扑结构来解释涡击穿的物理现象。为了确定涡旋倾斜和伸展在涡旋击穿中的重要性，本文将对轴对称涡旋流动和椭圆截面涡旋流动进行研究。为了支持这一理论，提出了一种新的实验装置，该装置由一个大的有机玻璃球和一个小的球体组成，油填充大的间隙。内部的球体被磁性地悬浮和旋转。该装置允许内部球体的非轴对称旋转，并且完全是非侵入性的：硬件和可视化方法（基于激光测速）都不会侵入到流动中。涡旋分解已被证明是一个基本的问题，其应用领域广泛，如空中交通安全，涡旋燃烧器和超音速燃烧器中的火焰保持，以及层流控制。大量的文献致力于研究这一现象；然而，对于其潜在的物理性质仍然没有达成共识。

A concurrent computational and experimental study will be conducted which focuses on explaining the physics of vortex breakdown through observing the kinematics of vortex lines of the flow, as well as their topology in bundles which constitute the vortex core. To establish the importance of vortex tilting and stretching in vortex breakdown, axisymmetric swirling flows as well as those with elliptic cross sections will be studied. To support the theory a novel experimental device is proposed which consists of a large Plexiglass sphere containing a smaller sphere and oil filling the large gap. The inner sphere is suspended and spun magnetically. The device allows for nonaxisymmetric spinning of the inner sphere and is fully nonintrusive: neither the hardware nor the visualization method (based on laser velocimetry) intrude into the flow. Vortex breakdown has proven to be a problem of fundamental interest with applications to areas as diverse as air-traffic safety, flame holding in swirl combustors as well as supersonic combustors, and laminar-flo w control. A vast body of literature has been devoted to the study of this phenomenon; however there is still no consensus as to its underlying physics.