Mixing in Inclined Dense Jets

Abstract

Experiments were performed using laser-induced fluorescence (LIF) and a microconductivity probe on turbulent dense jets inclined upwards at an angle of 60° into stationary environments. Such jets are frequently used to discharge industrial wastewaters. Time-averaged LIF images show concentration profiles that vary smoothly in space but instantaneous images show considerable patchiness. Dilution at the jet impact point was found to be higher than previously reported. Downstream from the impact point, the flow becomes predominantly horizontal with a complex additional mixing process that results in ultimate dilutions considerably higher than the impact dilution. The flow is highly turbulent in the vicinity of the falling jet with large concentration fluctuations. These fluctuations decay with distance due to turbulence collapse under the influence of density stratification. The end of the mixing zone is defined as the location where the intensity of the concentration fluctuations falls to 0.05 (i.e. 5%) of their mean value. Normalized expressions for dilution, rise height, and other properties were derived and experimental coefficients are presented from which these gross flow properties could be predicted.