Taylorian diffusion in mildly inhomogeneous turbulence

Taylor's theory of dispersion was extended to produce estimates of the far-field growth rate of the plume of a passive scalar in grid turbulence (GT) and in uniformly sheared flow (USF), both of which evolve in the streamwise direction. Expressions for the evolution of the plume width relative to the integral length scale of turbulence were also derived. The predictions of plume growth rate were tested against available data in both of these types of flows and were found to be accurate in an extensive region of USF and compatible with an extrapolated trend in GT, in which the available data did not extend very far from the scalar source. Although in both cases the measured half-width of the plume was comparable in magnitude to the streamwise integral length scale of the turbulence, the far-field approximation seemed to hold.