Experimental investigation of high-frequency transverse instability in Helmholtz resonator-coupled lean-premixed hydrogen combustor

Abstract

Recent experimental studies suggest that lean-premixed pure hydrogen combustion plays a central role in generating self-sustained pressure oscillations, preferentially coupled with high-frequency tangential modes in land-based gas turbine combustors. The triggering of such high-frequency combustion dynamics is known to be closely connected with relatively small, flashback-resistant, characteristic nozzle dimensions, and the structural and kinematic properties of the premixed hydrogen flames. To identify important trends in the transverse modal dynamics of hydrogen flames, here we conduct detailed measurements of multislit injector-driven hydrogen flame dynamics. We analyze the measured data using the wave decomposition technique for PDF-based statistical assessments of bimodality and nodal line orientation. Experimentally, the planar-to-transverse mode transformation is revealed to be controlled by the combined influence of flame temperature and thermal power, which ultimately leads to the development of well-defined standing modes at around 4.69 kHz under the most severe test condition. Using analytic modeling and rigorous validation measurements, we also investigate Helmholtz resonator-type passive stabilization and its impact on the integrated system's thermoacoustic states with respect to the change in purge air flowrate. Our results show that the coupled system does not retain many of the initial thermoacoustic properties, but instead undergoes prominent changes in the first tangential modal dynamics, progressively evolving from a large-amplitude bimodal to a low-amplitude unimodal state.