Vorticity Dynamics of An Exothermic, Spatially Developing, Forced, Reacting ShearLayer

摘要

The effects of combustion exothermicity on the vorticity dynamics of a low Machnumber, forced, spatially developing, high Reynolds number, reacting shear layer are investigated using the results of a two dimensional numerical simulation. The dynamical reaction is modeled by single step, irreversible, Arrhenius kinetics with a high Damkohler number, a moderate Karlovitz number, and significant beat release. The numerical solution is obtained using the Lagrangian transport element method. Results indicate that a fast exothermic reaction, with the concomitant density variation, modifies the shape, size, speed, and orientation of the large scale vortical structures and their downstream interactions, leading to an overall reduction of the cross stream growth of the mixing region. These changes are traced to the two primary mechanisms by which density variation due to heat release modifies vorticity: volumetric expansion and baroclinic generation. It is shown that the weakening of the vorticity due to volumetric expansion diminishes the cross stream mixing zone by aligning the eddy major axris with the flow direction. Baroclinic vorticity generation, on the other hand is responsible for the formation of a band of positive vorticity on the outer perimeter of the large eddies, whose vorticity is predominantly negative, which inhibits entrainment and alters the eddy interaction mechanism from pairing of adjacent eddies to tearing of smaller eddies by their larger neighbors. Both mechanisms contribute to the acceleration of the eddies in the streamwise direction.