A DNS study of propagation of either an infinitely thin passive interface or a reaction wave of a nonzero thickness in forced, constant-density, statistically stationary, homogeneous, isotropic turbulence was performed by solving Navier-Stokes equations and either level set or reaction-diffusion equation, respectively, with all other things being equal. The simulations covered a wide range of conditions, i.e. five different (from 0.5 to 10.0) ratios of the rms turbulent velocity u' to the laminar wave speed S_L^0, three different (2.1, 3.7, and 6.7) ratios of the integral length scale L_11 of the turbulence to the laminar wave thickness δ_F, three different turbulent Reynolds numbers, and two different Zeldovich numbers Ze = 6.0 and 17.1. Accordingly, the Damköhler Da and Karlovitz Ka numbers were varied from 0.2 to 13.5 and 0.55 to 36.2, respectively, thus, covering both flamelet and thin-reaction-zone regimes of premixed turbulent combustion. The computed fully-developed bulk consumption velocity is significantly reduced when L_11⁄δ_F is decreased, with the effect being most pronounced at the highest u'⁄(S_L^0 )=10. Moreover, the consumption velocity normalized using S_L^0 and obtained by simulating the self-propagation of an infinitely thin interface by solving the level set equation depends linearly on u'⁄(S_L^0 ). On the contrary, dependencies of the normalized consumption velocity on u'⁄(S_L^0 ), computed by solving the reaction-diffusion equation (which describes a reaction wave of a nonzero thickness), show bending, with the effect being increased by δ_F⁄L_11 . Under conditions of the present study, the bending effect is controlled by a decrease in the rate of a relative increase δA_F in the reaction-zone-surface area with increasing u'⁄(S_L^0 ). In its turn, the bending of the δA_F (u'⁄(S_L^0 ))-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.
|Status||Published - 2017|
|Evenemang||Tenth mediterranean Combustion Symposium - Napoli, Italien|
Varaktighet: 2017 sep. 17 → 2017 sep. 21
|Konferens||Tenth mediterranean Combustion Symposium|
|Period||2017/09/17 → 2017/09/21|