Numerical investigation of the behaviour of confined, impinging jets with assessment of advanced concepts to reduce unsteady pressure fluctuations in gas turbine testing facilities

大型试验台用于评估现代喷气发动机的性能。MDS航空支持公司是这些测试单元的领先设计和制造商。当大型发动机在高流速下运行时，他们观察到设施中某些部件上的大幅度、低频不稳定压力波动。随着时间的推移，这些都足以导致组件损坏。这导致测试单元停机以进行维修，这对于MDS及其客户是不期望的。该项目将研究减少不稳定压力波动的方法，并将导致与引起和控制压力波动幅度的气流行为相关的新知识。这个问题与射流冲击有关，但相关的几何形状和流速在过去没有得到广泛的研究。为了解决这一问题，将采用双管齐下的方法：一方面，将进行调查，以确定如何改变最直接受压力波动影响的部件的形状可以改变波动幅度;与此同时，将对起作用的基本物理过程进行更基础的研究，这将产生可以添加无源器件的设计建议以防止或减轻压力波动。这两种方法都将采用数值模拟的空气流在测试单元。特别是，一个非常准确，但复杂的模拟方法称为大涡模拟将用于捕捉相关的物理过程的细节。将使用这些模拟评估各种设计想法和修改，以确定哪些具有最大的潜在好处，以及为什么。

Large test cells are used to evaluate the performance of modern jet engines. MDS Aero Support Corporation is a leading design and manufacturer of these test cells. They have observed large amplitude, low frequency unsteady pressure fluctuations on some of the components in the facilities when large engines are operated in them at high flow rates. These are significant enough to cause damage to the components over time. This leads to test cell downtime for repairs which is undesirable for MDS and their customers. This project will investigate approaches to reduce the unsteady pressure fluctuations and will also lead to new knowledge related to the air flow behaviour which gives rise to and governs the magnitude of the pressure fluctuations.****The problem is related to jet impingement, but the geometry and flow speeds which are relevant have not been extensively studied in the past. To try to solve the problem, a two-pronged approach will be employed: on one hand, an investigation will be carried out to determine how changes to the shape of the components most directly affected by the pressure fluctuations can alter the fluctuation magnitudes; simultaneously a more fundamental study of the underlying physical processes at play will take place and this will yield design proposals for passive devices which could be added to the test cells to prevent or mitigate the pressure fluctuations. Both approaches will employ numerical simulations of the air flow in the test cell. In particular, a very accurate but complex simulation approach called Large Eddy Simulation will be used to capture the details of the relevant physical processes. Various design ideas and modifications will be assessed using these simulations to determine which have the most potential benefit, and why.**