The structure of turbulent diffusion. II - Diffusion near the turbulent interface

To investigate the diffusion phenomena in the intermittent region near the turbulent interface, theoretical and experimental studies are made on the material diffusion in the mixing region of a non-turbulent flow and a turbulent flow behind a grid with equal velocity. A new expression for the coefficient of eddy diffusion which takes into account the decay of turbulence is proposed. The calculated curves using this expression agree well with the experimental results. It is pointed out that a critical frequency plays a significant role in the phenomena near the turbulent interface and the large eddies whose frequency is lower than this critical value contribute only to the bulk convection. Standing on this fact, it is shown that the mean concentration distribution calculated by the method proposed in our preceding paper coincides with the measured results.