Turbulent Molecular Mixing in Gaseous Free Shear Flows

181 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2001.The flow regimes studied in this investigation span three main stages of shear layer development. Vortex mixing in the near field of an axisymmetric jet (ReD = 2300) is studied by using an acoustic pulse to obtain repeatable vortex formation and merging events. Results indicate that the mixing process is initially slow within the laminar vortex rollers, but a dramatic increase in mixing is detected prior to and during vortex coalescence. In the next stage of research, non-pulsed axisymmetric jets from ReD = 16,200 to 29,200 were used to study the transition to small-scale turbulence. This transition was found to take place near the average location of vortex merging, and resulted in a 20 to 25% drop in the mixed jet fluid volume fraction, a 30 to 35% drop in the preferred mixed jet fluid fraction, and a shift from stationary to hybrid radial probability density functions. In the final stage of research, fully-developed turbulence was studied in the far-field region of a planar shear layer with low- to high-speed velocity ratios of 0.25 to 0.44. Statistical analysis in this regime indicated that the physics of molecular mixing differs between the lowand high-speed fluids, and that molecularly mixed fluid quantities are not uniform across the shear layer.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD