Direct Numerical Simulation Analysis of High-Speed Compressible Turbulent Reacting Flows at Propulsion-Relevant Conditions

Abstract

A direct numerical simulation (DNS) of a propagating H2-air flame in a semi-confined geometry is performed and analyzed. Simulation setup imitates the flow conditions in the Turbulent Shock Tube (TST) facility developed by the University of Central Florida. This facility and numerical configuration are designed for the study of high-speed, highly compressible premixed turbulent flames over a broad range of conditions including extreme ones leading to the deflagration-to-detonation transition (DDT). Present DNS is performed using the code AthenaRFX with a simplified single-step Arrhenius kinetics model representing a stoichiometric H2-air mixture. The combustion regimes that are accessed using this realistic configuration are at simultaneously high turbulent length and velocity scales, which push the extreme boundaries previously studied regimes. Analysis of the overall flame dynamics shows that the displacement-based turbulent flame speed does not represent the turbulent burning velocity with sufficient accuracy at these extreme regimes. Turbulent flow speed and enstrophy analysis suggest strong turbulence amplification by the flame, in agreement with the results of prior DNS performed in a more idealized setting of a flame interacting with an externally driven homogeneous, isotropic turbulence. Ultimately, this thesis develops a complementary numerical and experimental platform for the fundamental studies of high-speed, highly compressible turbulent combustion regimes directly relevant to novel aerospace propulsion applications, such as scramjets and detonation-based engines.