Principles of non-intrusive diagnostic techniques and their applications for fundamental studies of combustion instabilities in gas turbine combustors: A brief review

Combustion instabilities are often manifested in modern fuel-lean gas turbine combustors. Investigating the mechanisms and developing control strategies for combustion instabilities in such systems are of practical importance and give rise to interesting scientific issues as large-amplitude pressure and heat release perturbations can lead to catastrophic and irreversible consequences on costly gas turbine hardware. In recent years, tremendous efforts have been made to achieve a deeper understanding of the periodic combustion oscillations in gas turbine engines with both advanced numerical simulations and experimental diagnostics. In the latter case, state-of-the-art, non-intrusive diagnostic techniques have been well adopted to conduct fundamental studies on combustion instabilities in gas turbine model combustors. For example, simultaneous time-resolved measurements with planar laser-induced fluorescence (PLIF) for characterizing flame structure and particle image velocimetry (PIV) for imaging flow field significantly contribute to the understanding of the role of flame-flow-acoustics coupling in the events of combustion instabilities, and to the development and validation of advanced numerical models. However, planar measurements can be restrictive when flames are not axisymmetric or exhibit complex large-scale three-dimensional (3D) dynamics, which are commonly encountered in practical combustion system when combustion instabilities occur. Therefore, more recently, new volumetric imaging techniques for combustion diagnostics have attracted considerable research efforts. This paper categorizes different advanced non-intrusive combustion diagnostic techniques, including their basic principles and especially applications for the study of combustion instability. Some of the recent progresses in the diagnostic techniques, such as computed tomography of chemiluminescence (CTC), volumetric laser induced fluorescence (VLIF), rainbow-PIV, etc., are also discussed. These volumetric combustion diagnostic techniques offer the advantage to measure both spatial and temporal characteristics of the flame/flow of interest, which will enable deeper insights into the nature of unsteady combustion in the future. This brief review is intended to be useful for both researchers and engineers to design and conduct further fundamental experiments on combustion instabilities in gas turbine engines. (C) 2018 Elsevier Masson SAS. All rights reserved.