The round jet in a uniform counterflow: flow visualization and mean concentration measurements

The structure and concentration field of a round water jet in a uniform counterflow is investigated using planar laser-induced fluorescence for jet to counterflow velocity ratios between 1.6 and 10.0. At low jet- to counterflow velocity ratios, the flow appears to be quite stable, with a nearly constant downstream extent and regular vortex shedding. As the velocity ratio increases, the flow becomes more unstable, with significant fluctuations along both the downstream and radial directions. The flow is quite sensitive to directional perturbations, with even slight inclinations of the jet with respect to the counterflow resulting in regular asymmetric vortex shedding and a decreased mean downstream extent. Data on the mean and maximum downstream extents, as well as the maximum radial extent of the flow at various velocity ratios, are shown. A simple model is introduced to explain the dependence of the normalized mean downstream extent of the flow upon the velocity ratio. In addition, mean concentration data are presented. The results suggest that there exists a core region of jet-like dilution in the flow.We wish to thank Dipl.-Ing. Olaf König, whose engineer's thesis laid the foundations for this work; Peter Schergun, who built much of the flow facility, and Dr. Dietrich Bechert, for his many valuable suggestions. MY's stay in Berlin was sponsored by the National Science Foundation Program for Research at Foreign Centers, contract number INT9202425, and an Alexander von Humboldt Foundation Research Fellowship.