An experimental and theoretical study of the turbulent coflowing jet

Experiments carried out recently on a family of axisymmetric coflowing turbulent jets with different nozzle to free-stream velocity ratios are described. Special care was taken to ensure top-hat velocity profiles at the nozzle exit so as to reduce the number of parameters associated with the initial conditions. This results in a collapse of the data without the need to introduce different effective origins for the streamwise coordinate. The mean flow behaviour is compared to self-preserving asymptotic forms and stresses are also examined to investigate the possibility of self-preservation. Comparisons are made with measurements of other workers in coflowing jets and axisymmetric wakes. Further information on the structure of the coflowing jet is found by examining the spectral Reynolds shear stress correlation coefficient, the premultiplied spectra and the high-wavenumber forms of the spectra. An analysis was carried out to see if the mean flow, Reynolds stress distributions and spectra are consistent with an inviscid ‘double-roller’ vortex structure for the representative large-scale energy-containing motions. Results show support for such a model.