Flame-generated turbulence in direct numerical simulations of the Turbulent Shock Tube facility

This talk presents results of direct numerical simulations (DNS) of fast, highly compressible, premixed turbulent flames. DNS are designed to model the Turbulent Shock Tube (TST) facility developed at the University of Central Florida. Turbulent flames in the TST exhibit highly unsteady behavior undergoing rapid acceleration driven by significant turbulence amplification, which can ultimately result in a deflagration-to-detonation transition. Detailed comparison of the DNS results with the experimental data is presented. Furthermore, analysis of the dynamics of the unsteady flames in the TST is discussed with the primary focus on the properties of the flame-generated turbulence as well as the mechanisms of turbulence production. It is shown that fast turbulent flames with burning speeds comparable to that of a Chapman-Jouguet deflagration are capable of generating turbulence with r.m.s. Mach numbers approaching 0.4 - 0.5 and Karlovitz numbers well in excess of 100. Finally, turbulence generation by the flame also results in the significant up-scale transport of kinetic energy, which can greatly energize motions on scales well above the laminar flame thickness. The nature of such up-scale energy transport, as well as its implications for the LES combustion models, is discussed.