On eddy diffusivity, quasi-similarity and diffusion experiments in turbulent boundary layers

Abstract

The experimental evidence of Poreh and Cermak [1] of two zones of quasi-similarity in a plume diffusing from a line source at the wall of a developed turbulent layer is carefully examined for consistency with the concepts of eddy diffusivity. The quasi-similarity of mean temperature profiles within a developed turbulent layer some distance downstream from a step in wall temperature observed by Johnson [2a], [2c], is similarly analysed. It is concluded that eddy diffusivities when viewed as properties of quasi-similar fields can account for the observed characteristics of the layer developing within another layer to the accuracy of observations. Some consequences of these concepts are explored.