Research data related to the publication "Reducing a lift-off distance of a nitrogen-diluted hydrogen flame evolving in a dry and humidified ambient flow through suction-driven global instability: Insights from LES".
This study employs Large Eddy Simulations (LES) to investigate the dynamics of lifted nitrogen-diluted hydrogen flames in a counter-current configuration, consisting of a central nozzle supplying fuel and an external coaxial suction nozzle. The system is placed in a stream of hot oxidizer, either dry air or humidified air with a water vapor mass fraction of 0.05. The simulations are performed for initial shear-layer thicknesses of the fuel jet (𝐷∕𝜃 = 40 and 56, where 𝐷 is the central nozzle diameter and 𝜃 is the shear layer momentum thickness). The dynamics of the flame base is analyzed under Kelvin–Helmholtz (K–H) and global instability (GI) regimes, with the latter induced by suction. The spatio-temporal variability of the flame lift-off position – from ignition to stabilization – is monitored using three diagnostic methods that incorporate temperature and OH radical conditioned on mixture fraction and radial flame position. In dry conditions, when the fuel jet undergoes K–H instability, relatively weak toroidal vortices form at axial distances of 4𝐷–6𝐷, leading to localized flame anchoring at 6.5𝐷–7.2𝐷 depending on 𝐷∕𝜃. In contrast, in the GI regime, the vortices are larger and stronger. Their periodic occurrence enhances mixing, resulting in a broader flame base anchored at a shorter distance (< 6𝐷). The mechanism driving the flame shift and widening is attributed to interactions between the flame base and the side jets generated by these vortices. Spectral analysis of temporal fluctuations of the lift-off distance reveals the presence of high-amplitude peaks, absent in the K–H regime, occurring at a low frequency that corresponds exactly to the side-jet formation frequency. In humidified air, oxygen availability decreases while the oxidizer’s heat capacity increases. As a result, if mixing is insufficient (K–H regime), the ignition is delayed and the flame lift-off distance increases dramatically (7𝐷 → 27𝐷). However, GI-induced vortices effectively shift the flame base upstream to approximately 17𝐷. Thus, the GI mechanism can be regarded as an effective flame-control strategy that may help prevent blow-off.
This work was supported by the National Science Center in Poland (Grant No. 2022/47/D/ST8/01902) and statutory funds of the Czestochowa University of Technology. We gratefully acknowledge Poland’s HPC Infrastructure (Cyfronet AGH and PCSS) for providing computer facilities (Grants PLG/2025/018542 and PL0241-01).
The readme file contains sorted filenames linked to the figures from the article.
(2026-03)
