DNS analysis of a three-dimensional supersonic turbulent lifted jet flame

Abstract

A fully compressible solver for direct numerical simulation of supersonic combustion has been developed and applied to investigate a three-dimensional spatially-developing supersonic turbulent jet flame. High-resolution bandwidth-optimized weighted essentially non-oscillatory scheme of spatial discretization and total variation diminishing temporal integration are used to capture the intricate phenomena with an accurate characteristic system and an updated detailed H2/air reaction mechanism. The numerical algorithms are first validated by simulating some canonical problems, and then used to analyze the global features, compressibility effects, and the stabilization mechanism of the supersonic lifted jet flame. It is found that the lifted flame consists of a stable laminar flame base with auto-ignition as the stabilization mechanism, a violent mixing region in which vigorous turbulent combustion occurs with both premixed and diffusion flames, and a far-field outer diffusion flame as well as an inner weaker premixed flame. Although diffusion combustion dominates the flame in general, premixed combustion is significant within the violent mixing region. The heat release rate in the high-speed region can be significantly influenced by the compressibility. In the region of fuel compressing, the heat release rate increases as the compressive power increases. While in the region of fuel expanding, the heat release rate also increases as the expansive power increases albeit with a smaller magnitude. The auto-ignition in a fuel-lean mixture near the most reactive condition is the main stabilization mechanism, which is determined from the statistical analysis of the heat release rate and the Damköhler number as well as the deduction of the lift-off height of the flame.