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 a re described. Special care was taken to ensure top-hat velocity profil es at the nozzle exit so as to reduce the number of parameters associa ted with the initial conditions. This results in a collapse of the dat a without the need to introduce different effective origins for the st reamwise coordinate. The mean flow behaviour is compared to self-prese rving asymptotic forms and stresses are also examined to investigate t he possibility of self-preservation. Comparisons are made with measure ments of other workers in coflowing jets and axisymmetric wakes. Furth er information on the structure of the coflowing jet is found by exami ning the spectral Reynolds shear stress correlation coefficient, the p remultiplied spectra and the high-wavenumber forms of the spectra. An analysis was carried out to see if the mean flow Reynolds stress distr ibutions and spectra are consistent with an inviscid 'double-roller' v ortex structure for the representative large-scale energy-containing m otions. Results show support for such a model.