DNS study of the bending effect due to smoothing mechanism

Artikel i vetenskaplig tidskrift, 2019

Propagation of either an infinitely thin interface or a reaction wave of a nonzero thickness in forced, constant-density, statistically stationary, homogeneous, isotropic turbulence is simulated by solving unsteady 3D Navier–Stokes equations and either a level set (G) or a reaction-diffusion
equation, respectively, with all other things being equal. In the case of the interface, the fully developed bulk consumption velocity normalized using the laminar-wave speed SL depends linearly on the normalized rms velocity u'/SL. In the case of the reaction wave of a nonzero thickness, dependencies of the normalized bulk consumption velocity on u'/SL show bending, with the effect being increased by a ratio of the laminar-wave thickness to the turbulence length scale. The obtained bending effect is controlled by a decrease in the rate of an increase AF in the reaction-zone-surface area with increasing u'/SL. In its turn, the bending of the AF(u'/SL)-curves stems from inefficiency of small-scale turbulent eddies in wrinkling the reaction-zone surface, because such small-scale wrinkles characterized by a high local curvature are smoothed out by molecular transport within the reaction wave.