Turbulent molecular mixing in fully-developed planar shear flows

Simultaneous NO and acetone planar laser-induced fluorescence is used to simulate a fast chemical reaction and provide the first instantaneous, resolution-independent images of molecularly-mixed fluid quantities in a fully-developed, gaseous planar shear layer. Velocity ratios ranging from 0.25 to 0.44 and two measurement locations are used to obtain values of Re_δ = ΔUδ/ν ranging from 18,600 to 103,000 and values of the "pairing parameter" ranging from 6.9 to 28.1. A "flip" experiment is used to obtain the mixed low- and high-speed fluid probability density functions, ensemble-averaged statistics, overall mixing efficiencies, and entrainment ratios at each test condition. Significantly different mixing dynamics are observed between the low- and high-speed fluids which shed new light on the mechanisms that contribute to the preferred entrainment of high-speed fluid. Results further indicate that a pseudo self-similar state is achieved relatively early, with statistics that vary across the shear layer. A slow evolution occurs, however, in the mixed-fluid statistics at higher Re_δ.