Quantitative visualization of high-Schmidt-number turbulent mixing in grid turbulence by means of PLIF

Abstract  

Quantitative visualization of high-Schmidt-number scalar fields has been performed in grid turbulence by means of a planar laser-induced fluorescence (PLIF) technique. The Reynolds number based on a mesh size of the grid is 2500 and the Schmidt number of the scalar is around 2100. To correct for the effects of various spatiotemporal variations such as quantum yield, a recently proposed correction method was introduced in the present experiment. In the present work, a PLIF experiment in combination with a calibration region installed outside of the test section is proposed. Visualizations of the instantaneous fluctuating scalar field suggest that mushroom-like structures accompanied by a pair of stirring structures, called engulfments, exist and contribute to large-scale scalar transfer. Visualization of the scalar dissipation field in the horizontal plane suggests that accumulation of the filament structures, which can be related to the mixing transition, locally exists around large-|c| regions, where |c| is the absolute value of the instantaneous fluctuating concentration. Thus, accumulation of the filament structures should be considered in the development of a turbulent mixing model for high-Schmidt-number scalar transfer.