The large-scale structure of turbulence in a co-flowing circular jet. (1st report. Turbulent intermittency and its spectral analysis).

The conditional average and spectrum of turbulent intermittency were determined experimentally in order to study the large-scale structure in a fully developed region of a jet at Re≒4×104. Turbulent intermittency functions, which were derived from hot-wire signals using a turbulent/non-turbulent decision, were used to obtain the zone average velocity and spectrum of intermittency. An interesting observation that the tips of turbulent bulges in far edge regions flowed slower than the co-flowing stream is attributed to the large-scale eddy motions in the intermittent region. As the time period in the turbulent intermittency functions correspond to the spatial length in the turbulent/non-turbulent interface, the spectra of intermittency functions are assessed to examine the length scale distributions of the large-scale structure. Walsh spectral analysis, which is suitable for the intermittency functions, reveals that the large-scale motions have no predominant scale but rather have many length scales longer than several-times the velocity half width.