Numerical Study of a Three-Dimensional Vortex Method

摘要

Numerical simulation is used to study mixing of a passive scalar in a spatially-developing shear layer at high Reynolds number. The numerical method is based on discretization of the vorticity and scalar gradients into finite-area elements and the transport of these elements along particle trajectories. Results show that mixing is governed by the entrainment of fluid from both streams into the large structures generated by the rollup of the vorticity layer. Local value of scalar concentration oscillates, due to the passage of these structures, between values limited by the Peclet number. Instantaneous scalar profiles exhibit mixing asymmetry and the skewness of concentration fraction within the eddies in favor of the high-speed stream. Mixing statistics of a passive scalar agree well with the experimental measurements of Masutani and Bowman in a two-dimensional shear layer, and emphasize the effect of molecular diffusion on mixing. The rate of burning in a single step Arrhenius chemical reactions between the two streams increases due to mixing enhancement, overcoming the decrease due to the strain field generated by rollup. Local product concentration is everywhere proportional to the vorticity, suggesting a new formula for turbulent combustion modeling. (Author) (KR)