Baroclinic Vorticity Generation Near the Turbulent/Non-turbulent Interface of a Boundary Layer with Combustion

Abstract

Enstrophy transport is examined in a recent direct numerical simulation database of compressible turbulent boundary layer featuring non-premixed hydrogen-air combustion. The inlet flow profile combines a cold, sonic hydrogen stream near the wall with a preheated, supersonic air mainstream, resulting in downstream transition and ignition phenomena, using a detailed chemistry scheme. Unlike reacting mixing layers or jets where the flame surface typically develops at regions of maximum shear intensity, in this configuration, the flame surface region is found beneath the boundary layer edge within one Taylor micro-scale of the turbulent/non-turbulent interface. While classical enstrophy budget analyses along the wall-normal direction reveal no significant deviation from non-reacting boundary layers, conditional budget analyses in the direction normal to the turbulent/non-turbulent interface unveil baroclinic torque production of comparable magnitude to vortex stretching in the turbulent sublayer. The relationship between local chemical heat release and baroclinic torque generation is investigated by evaluation of the integrand linked to the enstrophy variation from baroclinic torque at different heat release levels. The findings suggest that net torque variations are skewed towards positive values in the local flow regions of sufficiently high chemical heat release.