Work

Nonlinear dynamics and higher harmonic generation in velocity-forced reacting jet in crossflow

Year: 2026

Type: article

Abstract: The development of state-of-the-art gas turbines with an axially staged combustor requires an improved understanding of the dynamic response of a reacting jet in crossflow (RJICF) in the secondary combustion zone. In this study, we experimentally investigate the RJICF subjected to external velocity forcing in terms of its nonlinear behavior and the flame dynamics responsible for the generation of higher harmonics. Nonlinear dynamics are analyzed by means of higher-order spectral analyses and joint visualizations of phase-resolved OH planar laser-induced fluorescence and high-speed OH* chemiluminescence. Across all forcing frequencies, the amplitudes of both velocity and heat-release rate fluctuations exhibit a quadratic scaling relationship, with noticeable nonlinear transitions occurring between 11%–15% of the forcing amplitude. Spectral analyses — coherence and auto-bicoherence — considering the velocity, heat release, and the corresponding harmonics are conducted as a function of the forcing amplitude, demonstrating that the harmonic heat-release fluctuation appears to be related to its fundamental dynamics rather than the harmonic velocity fluctuation. The flame imaging results, OH planar laser-induced fluorescence (OH-PLIF) and high-speed OH* chemiluminescence, indicate that the vortex-interaction-induced structures evolve noticeably with an increase in the forcing amplitude. Such flame dynamics produce alternating regions of heat-release enhancement and suppression within the coherent structure, which oscillates at the fundamental frequency, thereby governing harmonic generation. Novelty and significance statement: The novelty of the present investigation lies in its detailed characterization of the nonlinear dynamics of the velocity-forced reacting jet in crossflow (RJICF) using higher-order spectral analyses combined with optical measurements. While nonlinear responses are expected in all flame configurations, our findings reveal that a specific quadratic scaling relationship is established for the premixed RJICF across a wide range of forcing frequencies and velocity amplitudes. Such dynamic characteristics of the RJICF measured in this study provide physically important, high-fidelity data to support and validate advanced CFD and low-order thermoacoustic modeling, particularly regarding harmonic generation and its influence on limit-cycle prediction [1] , [2] .

Source: Proceedings of the Combustion Institute

DOI: 10.1016/j.proci.2026.106537

Authors: Yongseok Choi, Kyu Tae Kim

Institution: Korea Advanced Institute of Science and Technology

Language: English

Topic: Combustion and flame dynamics

Subfield: Computational Mechanics

Field: Engineering

Domain: Physical Sciences

Open Access status: hybrid

Estimated APC paid: $3,570

Funders: Ministry of Trade, Industry and Energy, Korea Institute of Energy Technology Evaluation and Planning