Direct Numerical Simulations of Turbulent Lifted Hydrogen Jet Flames in Mildly Heated Coflows

Direct numerical simulations (DNSs) of the near field of three-dimensional spatially-developing turbulent hydrogen jet flames in heated coflows at the two intermediate temperatures of 750 and 950 K were performed with a detailed mechanism to elucidate the characteristics of the flame structures and to determine the stabilization mechanism. The DNSs were performed at a jet Reynolds number of 8,000 with 1.28 billion grid points. The results show that relatively-constant low flame speed stabilizes the lifted flame in the coflow of 750 K such that the oscillation of the flamebase is mainly attributed to the passage of large-scale flow structures of the fuel jet. However, for 950 K coflow case high flame speed in hot fuel-lean mixture at the flame base is the main source of the stabilization of the lifted jet flame. Chemical explosive mode analysis (CEMA) and Lagrangian tracking of the flamebase reveal the stabilization mechanisms of the two turbulent jet flames.