Experimental study on the mixing of high-schmidt-number scalar in regular/fractal grid turbulence

Abstract

High-Schmidt-number scalar mixing layers in a turbulent flow generated by regular and fractal grids are investigated by means of experiments using particle image velocimetry (PIV) and planar laser induced fluorescence (PLIF) technique. The Reynolds number based on the mesh size is 2,500. Rhodamine B is used as a fluorescent dye. The Schmidt number is about 2,100. The flow is separated into upper and lower layers by a splitter plate installed upstream of the grids; thus, the turbulent scalar mixing layers develop downstream of the grids. The results show that fractal grid turbulence has stronger turbulence intensity than that in regular grid turbulence. The decay exponent of turbulence intensity, n, is n = 1.21 for the regular grid and n = 1.40 for the fractal grid. The eddy diffusivity for mass in fractal grid turbulence is approximately four times larger than that in regular grid turbulence. The scalar dissipation in fractal grid turbulence is smaller than that in regular grid turbulence. Finally, it is concluded that turbulent scalar mixing is more enhanced by the fractal grid than by the regular grid. ©2013 The Japan Society of Mechanical Engineers.