Structure in the Near Field of the Transverse Jet

Photographs of a jet issuing from a wall into a crossflow display the four types of vortical structures which exist in the near field: namely, the jet shear layer vortices, the nascent far field vortex pair, the near-wall horseshoe vortices, and a system of vortices in the wake of the jet. It is shown that the wake vorticity is not “shed” from the jet but is formed from vorticity which originated in the wall boundary layer. The sources of vorticity for the other types of structures are also briefly discussed

Challenges in Turbulent Mixing with Combustion

Turbulent combustion combines the complexities of turbulence and mixing, challenges not met in the twentieth century, with the complexity and subtlety of chemical kinetics. This discussion focuses on progress and some turbulent-mixing issues in chemically reacting flows stemming from experimental, modeling, and direct-numerical simulation (DNS) studies. The mixing transition will be discussed. DNS studies of the Rayleigh-Taylor instability in miscible fluids reveal an early-time diffusive growth and a strong sensitivity to initial conditions. Recent experiments address the assumption of isotropy in turbulence and mixing. Experiments in high-speed shear layers elucidate some effects of compressibility on the mixed-fluid field. Issues involving molecular-transport coefficients will also be discussed