Numerical study of high-Reynolds number vortex flows with high-order accurate meshless vortex method.

流体的流动是一个非常难研究的课题，但它影响着我们生活的无数方面。了解心脏中的血液流动，喷气式客机产生的漩涡，笔记本电脑微芯片的冷却，以及大气中的空气和海洋中的水的流动，所有这些都需要流体动力学知识。流体动力学是一个非常具有挑战性和激动人心的科学领域。应用程序数不胜数，其复杂性也是如此。由于流体的一般物理描述导致了一个数学公式--一个微分方程式--通常无法求解，因此科学家们尝试使用计算机模拟，因为计算机模拟是可用的。事实上，计算科学中的许多进步都是努力解决某些流体流动问题的直接结果。有些流动即使用最强大的计算机也特别难解决。涉及多种尺寸的涡流、湍流或快速变化的流动就是主要的例子。但旋涡几乎无处不在地出现在流体中，它们导致了许多我们想要了解或控制的现象。例如，当我们听到直升机的噪音时，这种噪音在很大程度上是由一个桨叶被下一个迎面而来的桨叶撞击留下的涡流所产生的。而当飞机在接近着陆时被控制塔隔开时，主要是因为需要避免上一次降落时留下的涡流。如果我们对飞机漩涡的理解是这样的，我们可以预测它们在给定时刻的位置，那么下一架迎面而来的飞机的指令就可以安全地给出，同时考虑到机场的效率。通过这种方式增加降落频率可以节省大量的资金。要研究这类问题，计算方法是必不可少的。计算流体动力学领域涉及流体流动问题的计算机模拟。在这个领域，大多数科学家使用的方法是基于将存在流体的空间划分为小元素、正方形或三角形或立方体，其中的方程被称为离散的。例如，通过跟踪进入元素一侧和离开元素另一侧的流体量，就可以解出这些方程。这些方法已经使用了几十年，可以产生很好的效果。但很多时候，它们都有一个问题：它们扩散漩涡的速度太快。再次使用喷气式客机的例子，他们将预测尾流涡流已经消失，而实际上它们仍然存在，并对迎面而来的飞机构成危险。一些计算科学家一直在试验不同的方法，其中不使用流体的几何元素，而是使用一组不相连的点来计算感兴趣的量，如速度。这一领域被称为无网格或无网格计算。巴尔巴博士的研究集中在这一领域，使用点或流体粒子的计算结果能够解决流动中的小漩涡，并且不会太快地扩散它们。这些方法正在不断发展，最近的进展意味着有机会进行非常准确的模拟。BARBA的研究计划旨在开发一种基于涡旋粒子的先进方法，这种方法具有很高的精度。她将引入创新，更有效地计算流体中的一系列尺度，并开发智能方法来解释浸没在流体中的身体的存在。这些进展有望对无网格计算领域产生重大影响。此外，她将使用新方法来研究物理海洋学家和空气动力学家感兴趣的具体问题，包括涡旋的相互作用。这项研究的结果将在涡动力学和计算科学方面取得总体上的进展。

The flow of fluids is an unusually difficult subject to study, but it affects innumerable aspects of our life. The understanding of the flow of blood in the heart, the vortices created by jet airliners, the cooling of a laptop's microchip, and the flow of air in the atmosphere and water in the ocean, all of these require knowledge of fluid dynamics. Fluid dynamics is a very challenging and exciting field of science. The applications are countless, and so are the complexities. Because the general physical description of fluids results in a mathematical formulation --a differential equation-- which cannot in general be solved, scientists have attempted to use computer simulations since these were available. In fact, many advances in computational science are a direct result of the efforts to tackle some problem of fluid flow.Some flows are particularly difficult to solve, even with the most powerful computers. Flows involving eddies of multiple sizes, turbulence or rapid changes are the chief example. But vortices appear almost everywhere in fluids, and they are responsible for many phenomena that we would like to understand or control. For example, when we hear the noise of a helicopter, that noise is in great measure produced by the vortices left behind by one blade being hit by the next oncoming blade. And when airplanes are spaced by the control tower on approach to landing, it is mostly due to the need to avoid the vortices left behind by the previous plane landing. If our understanding of airplane vortices was such that we could predict where they are in a given moment, the instructions for the next oncoming plane could be safely given with airport efficiency in mind. A huge amount of money could be saved by increasing the frequency of landings in this way.To study these types of problems, the computational approach is essential. The field of Computational Fluid Dynamics involves computer simulations of problems of fluid flow. In this field, the majority of scientists use methods which are based on dividing the space where there is fluid into small elements, squares or triangles, or cubes, where the equations are said to be discretised. The equations are solved by, for example, keeping track of how much fluid enters one side, and leaves the other side, of the elements. These methods have been used for decades, and can produce excellent results. But many times they suffer from one problem: they diffuse the vortices too fast. Using again the example of the jet airliner, they would predict that the wake vortices are gone, when in fact they still persist and pose a danger to oncoming airplanes.Some computational scientists have been experimenting with different methods, where instead of using geometrical elements of fluid, a set of disconnected points are used to calculate the quantities of interest, like velocity. This field has come to be known as meshless or gridfree computation. The research of Dr Barba concentrates in this field, where the use of points, or fluid particles, results in calculations which are able to resolve the small eddies in the flows, and do not diffuse them too fast. The methods are in constant development, and recent advances mean that there is opportunity for very accurate simulations. The research programme of Barba aims to develop an advanced method, based on vortex particles, which is highly accurate. She will introduce innovations allowing the calculation of a range of scales in the flow, more efficiently, and develop clever ways of accounting for the presence of bodies immersed in the fluid. These advances promise to have a significant impact in the field of meshless computation. Moreover, she will use the new methods to study specific problems of interest to physical oceanographers and aerodynamicists, involving interaction of vortices. The results of this research will make progress in both vortex dynamics and computational science in general.