Viscous superlayer in a reacting compressible turbulent mixing layer

Abstract

Direct numerical simulations of temporally evolving reacting compressible mixing layers have been performed to study the viscous superlayer (VSL) at the outer edge of the interface layer. Budgets of the transport equation of enstrophy conditioned on the normal distance from the turbulent/non-turbulent interface are used to examine the features of the VSL. A new method is introduced to detect and to quantify the thickness of the VSL in reacting compressible flows. It involves finding the correlation coefficient of the viscous diffusion term with the viscous dissipation term. It is shown that, while compressibility seems to have little effect on the thickness of the VSL, as the level of heat release increases, the thickness of this layer decreases. Furthermore, it is observed that a thinner VSL propagates slower, resulting in a decrease of the rate of entrainment into the mixing layer.