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

将同时进行计算和实验研究，重点是通过观察涡线的运动学以及构成涡核的束状结构来解释涡旋破裂的物理机制。为了确定旋涡倾斜和拉伸在旋涡破裂中的重要性，我们将研究轴对称旋流和椭圆截面旋流。为了支持这一理论，提出了一种新的实验装置，它由一个大的有机玻璃球体和一个小的球体组成，并用油填充大的空隙。内部球体被悬浮并以磁性旋转。该设备允许内部球体的非轴对称旋转，并且完全不具侵入性：硬件和可视化方法(基于激光测速)都不会干扰流动。涡流破裂已被证明是一个基本的问题，其应用领域广泛，包括空中交通安全、旋流燃烧室和超音速燃烧室中的火焰保持以及层流流动控制。大量的文献致力于研究这一现象；然而，对于其基本的物理原理，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.