Prediction and Measurement of Thermoacoustic Improvements in Gas Turbines With Annular Combustion Systems

Abstract

Environmental compatibility requires low emission burners for gas turbine power plants.In the past, significant progress has been made developing low NO x and CO burners by introducing lean premixed techniques in combination with annular combustion chambers. Unfortunately, these burners often have a more pronounced tendency to produce combustion-driven oscillations than conventional burner designs. The oscillations may be excited to such an extent that the risk of engine failure occurs. For this reason, the prediction of these thermoacoustic instabilities in the design phase of an engine becomes more and more important. A method based on linear acoustic four-pole elements has been developed to predict instabilities of the ring combustor of the 3A-series gas turbines. The complex network includes the whole combustion system starting from both compressor outlet and fuel supply system and ending at the turbine inlet. The flame frequency response was determined by a transient numerical simulation (step-function approach). Based on this method, possible improvements for the gas turbine are evaluated in this paper. First, the burner impedance is predicted theoretically and compared with results from measurements on a test rig for validation of the prediction approach. Next, the burner impedance in a gas turbine combustion system is analyzed and improved thermoacoustically. Stability analyses for the gas turbine combustion system show the positive impact of this improvement. Second, the interaction of the acoustic parts of the gas turbine system has been detuned systematically in circumferential direction of the annular combustion chamber in order to find a more stable configuration. Stability analyses show the positive effect of this measure as well. The results predicted are compared with measurements from engine operation. The comparisons of prediction and measurements show the applicability of the prediction method in order to evaluate the thermoacoustic stability of the combustor as well as to define possible countermeasures. Downloaded From: http://gasturbinespower.asmedigitalcollection.asme.org/ on 05/24/2015 Terms of Use: http://asme.org/terms Fig. 16 Stability limits for different cylindrical burner outlet "CBO… configurations "Berendbrink and Hoffman †19 ‡… Journal of Engineering for Gas Turbines and Power JULY 2001, Vol. 123 Õ 565 Downloaded From: http://gasturbinespower.asmedigitalcollection.asme.org/ on 05/24/2015 Terms of Use: http://asme.org/terms

Experimental and Numerical Investigation of Thermoacoustic Sources Related to High-Frequency Instabilities

“…This assumption is widely used in industrial practice, when stability analysis of combustors is performed on the basis of the acoustic wave equation, using low-order network models, see e.g. Dowling [2], Schuermans et al [43], Krüger et al [44], or using 3D finite-element calculations, see e.g. Camporeale et al [45].…”

Impact of the Acoustic Forcing Level on the Transfer Matrix of a Turbulent Swirling Combustor with and Without Flame

“…It has long been recognized that a fraction of the acoustic energy is dissipated inside a burner submitted to sound waves [25,53,54]. This is generally modeled by a DATM expression with additional lump parameters, such as an effective length taking into account the inertia of the fluid and a pressure loss coefficient.…”

Progress in analytical methods to predict and control azimuthal combustion instability modes in annular chambers

“…However, it can be solved numerically to study non-normality and non-linear triggering, 60 for instance, due to non-trivial boundary conditions. 19 • Network model: Another approach is to solve the thermoacoustic problem using a quasi-1D description of the geometry, 30,65,[67][68][69][70][71] one of this approach being the ATACAMAC network model. 30,[70][71][72] A network model can be constructed using 1D tubes where acoustic propagation takes place only along the duct axis (characterized by a propagation matrix R i (ω)).…”

“…• Frequency-domain analysis: Another approach is to solve the thermoacoustic problem in the frequency domain. 30,65,[67][68][69][70][71] The acoustic fluctuations are assumed to be harmonic in time, which allows a Fourier representation of the complex acoustic pressure,…”

“…Recently, the need of considering non-symmetric combustors has appeared, mainly to investigate novel passive techniques to control azimuthal modes. For instance, introducing Helmholtz resonators, 69,79 baffles, 82 or different types of burners 67,83 may damp unstable modes but also break the rotational symmetry of the configuration. For the latter option, choosing which burner types must be mixed in a chamber and how to distribute them along the azimuthal direction to damp azimuthal modes are an open topic that analytical studies can help clarify.…”