The structure of the large eddies in fully developed turbulent shear flows. Part 1. The plane jet

A series of measurements, obtained using arrays of hot-wire anemometers, has been performed in the fully developed region of a plane turbulent jet. The anemometer output signals were simultaneously sampled, digitized with sufficient resolution for numerical linearization, and recorded on magnetic tape for subsequent analysis. The data was processed to extract information about the structure of the large eddies within the flow. Firstly, a selection of the two-point velocity correlation functions was evaluated, and diagrams of the contours of constant correlation for the stream wise velocity component were constructed. Secondly, an iterative procedure similar to the techniques generally described as ‘pattern recognition and image enhancement’ was used to form ‘ensemble’ averages of the two-dimensional patterns of the streamwise velocity component associated with the large eddies. The results indicate that the large eddies in the fully turbulent region of the flow are roller-like structures with axes aligned approximately either with the direction of the strain associated with the mean-velocity gradient or with the direction of homogeneity (spanwise). It was found that these basic structures tended to occur in various preferred combinations. Estimates were obtained for the total intensity contribution from the large eddies, the ranges of sizes and intensities of the individual structures, and their effective packing density.