The Development of Unstructured Mesh Technology for Viscous High Speed Flows

传统的航空航天飞行器设计涉及大量使用风洞来测试不同的配置和最终设计。然而，这是一个昂贵且漫长的过程，还需要使用针对特定流速设计的专业测试设备。随着计算机的出现，在过去的20年里出现了一种新技术，它提供了一个强大的工具来帮助空气动力学设计。控制空气运动的方程式在几个世纪前就已为人所知。然而，对于一般流，它们的解并不适用于经典的数学求解技术。随着高性能计算机的出现，一种基于在计算机上求解这些复杂方程的新技术出现了，它被称为计算模拟，或者更一般地说，科学模拟。模拟气流的基本概念是直截了当的。对控制气流的方程中的未知数进行近似，将少数高度复杂的方程转化为数百万个简单的方程。然后用计算机用算法的方法来解这些方程。在现实中，飞机周围的区域被细分为小的元素，在每个元素中，流量变量以某种适当和一致的形式近似。这种细分空间的过程称为网格生成。求解方程并反过来产生未知流量变量（如压力、密度等）的算法称为求解算法，这些算法的结构是为了确保从通常具有许多处理器的高性能计算机中获得最大效率。计算结果然后用计算机图形处理和重要的定量数据，如升力和阻力可以提取。这项技术现在在所有主要的航空公司中都是常规使用的。虽然没有使用多余的风洞，但该技术使设计师能够探索新的和创新的设计，并确保更少的几何形状需要进行昂贵的风洞分析。虽然高速流动的计算机模拟的基本概念很简单，但准确预测关键气动参数的要求是一项重大的技术和智力挑战。准确地表示飞机的几何形状需要创新的方式来表示三维表面和飞机周围元素的生成，这将使解决算法能够捕获所有复杂的物理现象，这仍然是一个挑战。虽然流体流动的方程可以精确地写出来，但可用计算能力的限制，即使考虑到世界上最大的计算机的能力，也要求研究人员做出近似，就像模拟湍流的情况一样。在某些情况下，这些近似不能捕获流的细节，因此预测不能准确地代表现实。该项目旨在专注于进一步的技术发展，以提高复杂气动形状（如完整的飞机配置）高速流动的准确性，同时确保计算可以在满足设计中遇到的实际项目最后期限的时间尺度内执行。特别是，该项目将专注于提高我们准确预测空气动力学参数（如升力和阻力）的能力，并模拟飞机在起飞和着陆配置时产生的高度复杂的流场，因为地面影响可能很明显。当这些开发完成后，计算机预测将与实际测试数据进行比较，以确保技术的适当验证。

Traditional design of aerospace vehicles has involved the extensive use of wind tunnels to test different configurations and to finalise design. However, this is an expensive and lengthy process that also requires the use of specialist test facilities designed for particular flow speeds. With the advent of the computer a new technology has emerged over the last 20 years that provides a powerful tool to aid aerodynamic design. The equations that govern the movement of air have been known for several centuries. However, for general flows, their solution is not amenable to classical mathematical solution techniques. With the advent of high performance computers, a new technology, termed computational simulation or, more generally, scientific simulation, that is based upon solving these complicated equations on the computer, has emerged. The basic concepts involved in simulating airflow are straightforward. Approximations to the unknowns in the equations that govern airflow are made that transforms the few highly complicated equations into millions of simple equations. The computer is then used to solve these equations using an algorithmic approach. In reality, the region around an aircraft is subdivided into small elements and within each element the flow variables are approximated in some appropriate and consistent form. This process of subdividing the space is termed mesh generation. The algorithms that solve the equations and in turn produce the unknown flow variables (such as pressure, density etc) are called the solution algorithms and these are structured to ensure that maximum efficiency can be obtained from high performance computers that will, in general, have many processors. The results of the calculations are then processed using computer graphics and important quantitative data such as lift and drag can be extracted.This technology is now used routinely in all major aerospace companies. Whilst not making the use of the wind tunnel redundant, the technology has enabled designers to explore new and innovative designs and ensure that fewer geometries need to be subjected to costly wind tunnel analysis.Whilst the basic concepts of computer simulation for high speed flows are simple, the requirement to predict accurately key aerodynamic parameters represents a significant technical and intellectual challenge. Representing the geometry of an aircraft accurately demands innovative ways of representing three-dimensional surfaces and the generation of the elements around the aircraft that will enable the solution algorithm to capture all the complex physics still remains a challenge. Whilst the equations of fluid flow can be written exactly, the restrictions in available computing power, even taking into account the capabilities of the World's largest computers, require researchers to make approximations, as is the case for the simulation of turbulent flow. For some cases, these approximations do not enable the details of the flow to be captured and hence the predictions do not accurately represent reality. This project is aimed at focusing on further technical developments that will increase the accuracy of high speed flows for complicated aerodynamic shapes, such as complete aircraft configurations, whilst ensuring that the computations can be performed in a time scale that meets real-world project deadlines encountered in design. In particular, the project will focus on enhancing our capability to predict aerodynamic parameters accurately, such as lift and drag, and to simulate highly complicated flowfields generated when an aircraft is in take-off and landing configuration where ground effects can be significant. When these developments have been completed, computer predictions will be compared with real test data to ensure appropriate validation of the techniques.