Displacement Speed Analysis Of Surface Propagation In Moderately Turbulent Premixed Reacting Waves

The propagation of premixed reacting waves can be characterized by a displacement speed S-d at which the local surface of the reaction progress scalar moves respective to flow. Often, S-d is considered through decomposition into three parts of contribution due to the tangential diffusion of curvature, normal diffusion, and reaction. A set of recently derived transport equations for S-d and three of its decomposed parts provides new diagnostics for better understanding reaction wave propagation in a turbulent environment. In this work, those diagnostics are applied on four similarly setup direct numerical simulation cases studying the propagation of moderately perturbed planar reaction waves into homogeneous turbulence, and the reaction waves differ by the density ratio between fresh and burned gases. The data analysis reveals four self-acceleration behaviors: (i) surfaces propagating at large positive (negative) S-d tend to advance (retreat) faster, (ii) surfaces having large positive (negative) curvature tend to become more curved positively (negatively), (iii) thicken wave zones tend to become thicker, and (iv) surface elements accelerate toward their destruction. The extent of the above accelerations all reduces in the reaction wave having a high density ratio. This can be attributed to the turbulence inhibition due to the flow dilatation and viscosity increase across a thermal-expansion enabled reaction wave. The distribution of curvature for the reaction-zone surface skews toward a negative value, i.e., the curvature center pointing to the burned product.