Lagrangian analyzes of complex and turbulent flows for advanced flow diagnostics

用于高级流动诊断的复杂湍流的拉格朗日分析

• 批准号: RGPIN-2019-04711
• 负责人: Vétel, Jérôme
• 金额: $ 1.97万
• 依托单位: École Polytechnique de Montréal
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2022
• 资助国家: 加拿大
• 起止时间: 2022-01-01 至 2023-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=754524
• 关键词: Lagrangian; analyzes; complex; turbulent; flows

Fluid mechanics is a centuries old science in which many concepts have been defined to describe fluid flows. For example, everybody knows what is a vortex, however, the very definition of a vortex is still not available, while this is probably one of the most used concept in fluid mechanics. A reason that explains this observation is that many criteria that are traditionally used are not objective. Objectivity means independency with respect to the observer, which namely allows to define physical quantities that are independent of the reference frame. In the example of the vortex, a tornado should be detectable from earth or from a satellite independently of its movement, and moreover, its properties have to be the same in both reference frame, which is not so obvious. Fluid mechanics has been historically approached with Eulerian tools, which means that the information is gathered in time from a fixed point in space. This is in fact the easier or only way to measure a quantity, as a probe is always motionless in a wind-tunnel while the fluid is moving, or a Pitot tube is fixed to an aircraft during a flight to measure its speed. The counterpart of a Eulerian quantity is said to be Lagrangian. In a Lagrangian frame, fluid particles are on the contrary followed in their movement. This is indeed made possible today because we have easily access to data in space and time through numerical simulations or most advanced state-of-the-art measurement techniques. It turns out that many Lagrangian quantities are objective, which opens a broader field of tools to study fluids in motion. The proposed research program aims at exploring what recently developed Lagrangian tools can tell us on fluid flows. For example, the phenomenon of flow separation, which occurs when a layer of fluid separates from a solid surface, inducing for example the aerodynamic stall on an aircraft wing, still can not be detected, and therefore predicted, but a recent Lagrangian theory could solve this problem soon. More generally, the Lagrangian frame provides a perception of many fluid flow mechanisms differing from traditional approaches, which induces new ideas, and allows to solve some challenging problems or to revisit some concepts. A large variety of flows will be examined, coming from both numerical simulations or experimental databases, from simple to most complex flows, such as turbulence. In particular, we will focus on biological flows that are difficult to analyze because of the high three-dimensionality and the temporal pulsation dependence.

流体力学是一门有着数百年历史的科学，其中定义了许多概念来描述流体流动。例如，每个人都知道什么是漩涡，然而，漩涡的定义仍然是不可用的，而这可能是流体力学中最常用的概念之一。解释这一观察结果的一个原因是，传统上使用的许多标准并不客观。客观性意味着相对于观察者的独立性，即允许定义独立于参考系的物理量。在涡旋的例子中，龙卷风应该是可以从地球或卫星上检测到的，而与它的运动无关，而且，它的特性必须在两个参考系中相同，这一点并不明显。流体力学在历史上一直是用欧拉工具来处理的，这意味着信息是从空间中的一个固定点及时收集的。事实上，这是测量一个量的最简单或唯一的方法，因为当流体流动时，探针在风洞中总是静止不动的，或者在飞行期间将皮托管固定在飞机上以测量其速度。欧拉量的对应量称为拉格朗日量。在拉格朗日坐标系中，流体粒子的运动则相反。这在今天确实成为可能，因为我们可以通过数值模拟或最先进的测量技术轻松获取空间和时间数据。事实证明，许多拉格朗日量是客观的，这为研究运动中的流体开辟了更广阔的工具领域。拟议的研究计划旨在探索最近开发的拉格朗日工具可以告诉我们流体流动。例如，当流体层从固体表面分离时发生的流动分离现象，例如引起飞机机翼上的空气动力失速，仍然不能被检测到，因此不能被预测，但是最近的拉格朗日理论可以很快解决这个问题。更一般地说，拉格朗日框架提供了许多不同于传统方法的流体流动机制的感知，这引发了新的想法，并允许解决一些具有挑战性的问题或重新审视一些概念。大量的各种流动将被检查，来自数值模拟或实验数据库，从简单到最复杂的流动，如湍流。特别是，我们将专注于生物流，因为很难分析的三维度和时间脉动的依赖。