Characterisation of NGV responses for LFR prediction - Low Frequency Rumble Transfer Functions

低频隆隆声（LFR）和实际上燃烧热声不稳定性可以是燃气涡轮机发动机的关键问题。它们不仅会对排放产生不利影响，而且会导致燃烧不稳定，甚至对燃烧室造成结构损坏。在燃气涡轮机发动机的设计过程中，为避免在发动机开发计划的后期阶段进行预期的设计变更，当物理试验通常不可能时，预测给定设计的LFR的能力是特别重要的。这项工作的目的是提供一个基本的了解LFR现象。这包括理解与LFR现象相关的燃烧室内发生的各种不稳定放热机制。此外，还可以考虑NGV如何通过层次分析（大涡模拟的准一维解）对来自燃烧过程的直接声波和熵波做出反应，从而可以通过考虑正确的上游行进声波来开发准确的预测方法。该方法可以潜在地提供结合传递函数（例如火焰传递函数）、不可压缩低速流模拟和声学建模的方法。与直接对整个燃烧室进行全可压缩燃烧模拟相比，具有显著的效率优势。该项目还将研究系统的脉冲响应直接强制不可压缩模拟，其中LFR模式是可能被捕获。这在计算上仍然比完全可压缩燃烧使能的模拟要求低得多。

Low frequency rumble (LFR) and indeed combustion thermoacoustic instability can be a critical issue of gas turbine engines. Not only they can adversely affect the emission, but also cause combustion instability and even structural damages to a combustor. The ability to predict LFR for a given design is particularly important during the design processes of gas turbine engines, when physical testing is often not possible, in order to avoid expect design changes at the later stages of an engine development programme. The work is aimed at providing a fundamental understanding of the LFR phenomena. This includes understanding the various unsteady heat release mechanisms that occur within the combustor that is associated with the LFR phenomena. In addition, consideration may also be given to how the NGV reacts to direct acoustic waves and entropy waves from the combustion process by a hierarchy of analyses (quasi-1D solutions to large eddy simulations), so that accurate prediction methods can be developed by accounting for the correct upstream travelling acoustic waves. The approach can potentially deliver a methodology of combining transfer functions (e.g. flame transfer function), incompressible low speed flow simulations and acoustic modelling. Compared to a direct fully compressible combustion simulation of the whole combustor, it has significant efficiency advantages. The project will also investigate the system's impulse responses to directly forced incompressible simulations, among which the LFR modes are possible to be captured. This is still computationally much less demanding than fully compressible combustion enabled simulations.