Effects of gravity on turbulent nonpremixed flames

The paper examines the effects of buoyancy on the behavior of turbulent nonpremixed flames using the method of direct numerical simulation. We examine the effects of the interactions between turbulence, chemical reaction, and buoyancy on the fields of vorticity, turbulence kinetic energy, scalar dissipation, and reaction rate. In the buoyant flame, the baroclinic torque creates strong counter-rotating vortices saddling the flame surface. These vortices result in a significantly more wrinkled flame surface than in the nonbuoyant case. One of the effects of wrinkling is that it reduces the distances between the isosurfaces of the mixture fraction F, thus augmenting the local ∇F and the scalar dissipation εF, and consequently the reaction rate ṙT. The zones of maximum ṙT coincide with those of maximum tangential extensional strain. Our results show a direct correlation between εF and ṙT for both the buoyant and nonbuoyant flames.