EFFECTS OF WAKES ON SHOCK-FLAME INTERACTIONS AND DEFLAGRATION-TO-DETONATION TRANSITION

摘要

Two-dimensional reactive Navier-Stokes numerical simulations are used to examine the effects of wakes behind obstacles on shock-flame interactions and deflagration-to-detonation transition in shock-tube experiments. The computations are performed for low-pressure (100 Torr) ethylene/air mixtures using a dynamically adapting computational mesh to resolve flames, shocks, wakes, and vortices in flow. Results of the simulations show that the effect of wakes is similar to the effect of boundary layers studied earlier. The velocity gradient in the wake causes the reflected shock to bifurcate. If the obstacle is large enough, the recirculation area behind the bifurcated shock can entrain the flame, thus accelerating it. The resulting reactive bifurcated structure contains two leading oblique shocks followed by a flame captured by the recirculation flow. This structure grows quickly. Reflections of the oblique bifurcated shocks from side walls create strong Mach stems that can produce hot spots, new flames, and eventually a detonation. The computational results are consistent with experimental observations of flame acceleration behind reflected shocks.