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

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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.