Abstract
Combustion instabilities, known as “rumble” and “screech” are the self-excited aerodynamic instabilities in the gas turbine combustor. They cause the premature failures of the gas turbine components, and, consequently, the failure of the gas turbine as a whole. Because of the complex physical effects underlying the rumble and the screech phenomena, it is difficult to eliminate them completely at the design stage. Therefore, special attention should be paid to the detection of the combustion instabilities in the gas turbine in order to prevent its prolonged operation in this mode. There are known techniques, which are able to detect the rumble and the screech in gas turbines. Most of them do not consider the combustion instabilities as non-linear and non-stationary events and, therefore, have lower detection efficiency. Novel technique for in-service combustion instability detection is implemented in this paper. This technique overcomes the limitations of the existing solutions.
Highlights
The combustion instabilities can be caused by multiple reasons
Following the undertaken literature review, the novelty of this paper is that the rumble is considered as non-stationary and non-linear event for the first time to the best of authors’ knowledge and in order to provide the best efficiency of the detection the non-stationary and non-linear techniques: the short time bicoherences based on the Fourier transform and the short time chirp Fourier transform are implemented and their efficiencies are estimated
It was found that the bicoherence based on the short time chirp Fourier transform allows for more effective rumble detection in comparison with the bicoherence based on the Fourier transform using the optimal signal processing parameters for both techniques
Summary
The combustion instabilities can be caused by multiple reasons. According to Williams (1985) the instabilities in combustion can be classified based on the size of the components involved in the instability formation: intrinsic (local and short distance interactions in the flow; high frequency of the effect), chamber (medium size instabilities, such as coupling of vortices in the flow with the flame front; medium frequencies) and system Considering the mentioned above features of the rumble the combustion instabilities can be characterized as a very complex, non-linear and non-stationary effects, which require application of the corresponding signal processing techniques for the effective in-service detection Another challenge in the combustion instability detection is associated with the growing interest to the integrated turbine health monitoring systems (Grabill, Seale, Wroblewski & Brotherton, 2002) able to perform the monitoring of the turbine condition using the minimum number of sensors, preferably accelerometers, as this provides cost effective, flexible and more reliable solution in comparison to use of the pressure transducers, especially high temperature ones.
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