Influence of Reynolds Number on the Evolution of a Plane Air Jet Issuing From a Slit

Abstract

Jet flows are encountered in a variety of industrial applications. Although from the points of view of manufacturing with ease and small spatial requirement it is convenient to use short slit nozzles, most of the available studies deal with turbulent jets issuing from contoured nozzles. In the present work, experiments have been conducted in the moderate Reynolds number range of 250–6250 for a slit jet. Mixing characteristics of slit jets seem to be quite different from those of jets emerging out of contoured nozzles. This is primarily due to the differences in the decay characteristics and the large scale eddy structures generated in the near field, which are functions of the initial momentum thickness. It is evident that, in the range of 250⩽Re⩽6250, the overall spreading characteristics of the slit jet flow have stronger Reynolds number dependence than those of contoured nozzle jets. In particular, the slit jets exhibit slower mean velocity decay rates and slower half-width growth rates. Normalized power spectra and probability distribution functions are used to assess the spatial evolution and the Reynolds number dependence of jet turbulence. It is seen that the fluctuating components of velocity attain isotropic conditions at a smaller axial distance from the nozzle exit than that required for mean velocity components to become self-similar.