The interference of multiple line sources in grid turbulence

The interference of two (and more) thermal line sources in decaying grid turbulence is studied by using the inference method described by Warhaft (1981) to determine the cross-correlation coefficient rho between two sources. The evolution of rho as a function of downstream distance, for d/2 in the range from 0.075 to 10, where d is the wire spacing and 2 is the length scale of the turbulence, is determined for a pair of sources located at various downstream distances from the grid (xo/M varying from 5 to 60 where xo is the distance of the sources from the grid and M is the grid mesh length). It is shown that a mandoline (Warhaft and Lumley, 1978) may be thought of, in a more fundamental way, as the interference of a number of line sources. Thus new light is shed on the rate of decay of scalar dissipation. New data for the thermal field very close to a line source is also presented.