Observations of jets in density stratified crossflows

Abstract

The results are presented of a water tunnel study undertaken to determine the characteristics of a circular jet in a density stratified crossflow. Flow visualization indicates that the salient characteristics include a stable potential core of length L in the vicinity of the jet exit. The length of the stable potential core depends on the velocity ratio α = U J U ∞ and the non-dimensional frequency ND U ∞ . As α is increases the value of L increases; L also increases for increasing values of ND U ∞ < 0.03 . However, L decreases with increasing ND U ∞ for values of ND U ∞ > 0.03 . Knowledge of this variability is necessary for quantifying mixing rates. Further downwind, the jet trajectory evolves to a maximum height of rise z m , and subsequently relaxes to a lower equilibrium level, z e. Values of z m and z e are in agreement with the predictions of scaling arguments. Mean density measurements indicate rapid increase of dilution for small distances from the jet exit; however, for large distances predominantly horizontal mixing processes result in much slower increase of dilution with distance.