| Direct numerical simulations (DNS) were performed of an idealized reacting, momentum driven jet to study effects of heat release and nonequilibrium chemistry in turbulent flames. The spectral element techniques was used to solve the full three-dimensional, unsteady equations of motion for a reacting turbulent jet. A low Mach number approximation was employed that filters out acoustic waves and the time-stepping stability constraints associated with them.; Simulations were performed for both two- and three-dimensional flows over a wide range of parameters. Parameters varied included the amount of heat release, Damkohler and Zeldovich numbers, and the amplitude of the initial perturbations to the velocity field. A key result of this work is an illustration of the coupled effects of heat release and nonequilibrium chemistry. Heat release, which has been shown to stabilize the fluid dynamics, generally causes a slower development of the jet and lower mixing rates, resulting in less product formation. However, this study demonstrated that this also lowers the magnitude of the scalar dissipation rate, which leads to a delay in the local extinction when nonequilibrium chemistry is included. The key parameters in characterizing this behavior are the scalar dissipation rate and the Damkohler number.; Physical mechanisms behind this behavior were studied using both turbulence energetics and vorticity dynamics. The heat release was shown to significantly decrease the magnitude of the turbulent kinetic energy and the vorticity. Examination of the vorticity equation showed significant effects of both thermal expansion and baroclinic torques in redistributing the vorticity in the heat release cases. A comparison of turbulence statistics for cases with and without heat release illustrated that the main differences between the two can be accounted for directly through the change in density. This can assist in the modeling of reacting flows. |
