Investigation of passive scalar mixing in a confined rectangular wake using simultaneous PIV and PLIF

A combined particle image velocimetry (PIV) and planar laser-induced fluorescence (PLIF) system was employed to investigate the turbulent mixing in a confined liquid-phase rectangular-wake flow with a Reynolds number based on hydraulic diameter of 37,500 and a Schmidt number of 1250. The simultaneous velocity and concentration field data were analyzed for flow statistics such as turbulent fluxes, turbulent viscosity and diffusivity, and turbulent Schimdt number. The stream wise and transverse turbulent fluxes were found to be of the same magnitude. The turbulent flux vector was not aligned with the mean concentration gradient. The turbulent Schimdt number was about 0.8. The spatial correlations of turbulent fluxes and concentration fluctuations were evaluated. In the R-u'phi' correlation field, there were a positive and a negative vertically oriented elliptical correlation region, which were symmetric around the basis point. The R-v'phi' correlation region was a horizontally oriented ellipse with negative values of the correlation coefficient. The correlation field of R-phi'phi' was also an ellipse with a horizontal major axis. The behavior of large-scale structures in both the velocity and concentration field was studied using linear stochastic estimation with a defined event of concentration fluctuation. Vortex streets were observed in the estimated velocity fields. The streamwise growth of the structure size increased linearly initially but then grew more slowly. (C) 2010 Elsevier Ltd. All rights reserved.