The role of hydrodynamic instability in flame-vortex interaction

The interaction between a flame and a vortex pair is investigated by a front-tracking numerical method, developed for multifluid flows, in which a sharp interface separates incompressible fluids of different densities and viscosities. It is shown that, in a weak vortical flow field, the initial vortex simply serves as an initiation agent for the onset of flame front hydrodynamic instability, which in turn dominates the evolution of flame wrinkling and postflame vorticity generation. The flame-generated vorticity (FGV) is of opposite sign of the incoming vortices and is due to the barochnic torque formed by the density gradient across the flame and the pressure gradient along the wrinkled flame surface. The relevance of the hydrodynamic instability is further demonstrated by analyzing the flame dynamics with the instability mechanism suppressed by imposing a perturbation length scale with minute growth rate. For sufficiently strong vortices, however, results show that while flame wrinkling is dominated by the incoming vortices, the FGV is affected by the combined pressure gradients of the vortices as well as that of the hydrodynamic instability. In fact, the only situation in which the course of the incoming vortices is preserved is for flames with small thermal expansion and thereby weak hydrodynamic instability influences.