Experimental investigation of mass transfer in a grid-generated turbulent flow using combined optical methods

The aim of this paper is to provide some significant experimental results for the mass diffusion process from a point source in a quasi-isotropic homogeneous turbulent field generated by means of a grid. Experimental data for the mean, the fluctuating concentration fields, and the turbulent mass flux, which is the cross-correlation between concentration and velocity, are provided. Two combined optical non-intrusive methods, laser-induced fluorescence and laser Doppler velocimetry, have been used to measure simultaneously and instantaneously the concentration of the passive contaminant and the velocity of the flow. The experimental results are compared with a theoretical development, including the concept of turbulent diffusivity. An experimental determination of the turbulent diffusivity is also performed. (C) 1997 Elsevier Science Ltd.