Experimental Investigation of Self-Excited Combustion Instabilities in a Lean, Premixed, Gas Turbine Combustor at High Pressure

Abstract

Self-excited combustion instabilities in a high pressure, single-element, lean, premixed, natural gas (NG) dump-combustor are investigated. The combustor is designed for optical access and instrumented with high frequency pressure transducers at multiple axial locations. A parametric survey of operating conditions including inlet air temperature and equivalence ratio has been performed, resulting in a wide range of pressure fluctuation amplitudes (p′) of the mean chamber pressure (pCH). Two representative cases, flames A and B with p′/pCH=23% and p′/pCH=12%, respectively, both presenting self-excited instabilities at the fundamental longitudinal (1L) mode of the combustion chamber, are discussed to study the coupling mechanism between flame-vortex interactions and the acoustic field in the chamber. 10 kHz OH*-chemiluminescence imaging was performed to obtain a map of the global heat release distribution. Phase conditioned and Rayleigh index analysis as well as dynamic mode decomposition (DMD) is performed to highlight the contrasting mechanisms that lead to the two distinct instability regimes. Flame interactions with shear layer vortex structures downstream of the backward-facing step of the combustion chamber are found to augment the instability magnitude. Flame A engages strongly in this coupling, whereas flame B is less affected and establishes a lower amplitude limit cycle.

Coupled interactions of a helical precessing vortex core and the central recirculation bubble in a swirl flame at elevated power density

“…DMD was first applied to non-reacting jets where it identified the spatial structure and frequency of the jet's vortex shedding [26,27]. DMD has since been extended to the analysis of numerous experimental and numerical efforts in understanding the coupling between hydrodynamics and the resulting thermoacoustics [28][29][30][31][32][33]. Variants of DMD have been proposed to tackle specific problems such as resolving transient and quasi-periodic dynamics [34].…”

Injector-coupled transverse instabilities in a multi-element premixed combustor

“…The design maintains similarities with several other rocket and gas turbine combustion experiments studied at Purdue University. 35,[37][38][39][40] VIPER-M was designed to promote self-excited, transverse instabilities while operating at a mean chamber pressure up to 825 kPa with an inlet air temperature up to 510 K. The multi-element configuration supports jet-stabilized combustion with flames anchored at the injector-exit plane (y ¼ 0), as labeled in Figure 1. This injector configuration is similar to the FLOX V R combustion experiments, which have been widely studied.…”

Three-Dimensional Numerical Analysis of Longitudinal Thermoacoustic Instability in a Single-Element Rocket Combustor

“…In addition, various instability modes have been found in CVRC experiments via continuously changing the oxidizer post length. These experiments provided abundant diagnoses of the combustion flow field, such as dynamic pressure (Sisco, 2007), temperature (Buschhagen et al, 2018), and chemiluminescence (Bedard et al, 2014). The results indicated that the combustion chamber step height and oxidizer post length have a significant influence on combustion instability.…”