Effects of initial mixture fraction on the development of a turbulent reactive mixing layer

Abstract

The effects of the initial mixture fraction distribution on the transition of a temporally developing turbulent reactive mixing layer is investigated using large-eddy simulation. The compressible Navier–Stokes equations along with the mixture fraction equation are solved. In contrast to the previous studies, where the initial mixture fraction is not perturbed, different probability density function distributions for the mixture fraction perturbations are considered. It is shown that when the initial mixture fraction is not perturbed, a strong initial pressure wave develops during the early stages of transition, and the compressibility effects become dominant. Perturbing the initial mixture fraction reduces the compressibility effects. The compressibility effects result in the direct supply of kinetic energy to the flow, and both the mean and turbulent kinetic energies increase during the initial period of development. An order of magnitude analysis is performed to understand the influence of initial mixture fraction distribution on the compressibility of the flow at the early stages of development. In addition, by using the characteristic form of the Euler equations, impact of the initial mixture fraction distribution on the development of the initial pressure wave is further clarified. Furthermore, the energy exchange between the mean and turbulent kinetic energies is studied by considering the time evolutions of dissipation, production, and pressure dilatation terms. Finally, the time evolution of the flame surface geometrical structure has been discussed.