Effect of Nozzle Orientation on Dense Jets in Stagnant Environments

Abstract

Laboratory experiments on single dense jets oriented at angles from 15° to 85° to the horizontal are reported. The major flow properties were measured by laser-induced fluorescence at the maximum rise height, impact point, and, for the first time, at the end of the near field. The impact point dilution was insensitive to nozzle angle over the range of about 45–65°. Because the additional mixing that occurred in the spreading layer beyond the impact point depended on nozzle angle, the near-field dilution was more sensitive to nozzle orientation and was highest for 60°, consistent with generally accepted design practice. Bottom boundary effects on dilution were also addressed. Along the jet centerline, time-average dilution first increased and then actually decreased in a thin layer up to the wall. The concentration increase near the bed is due to an increase in turbulent intermittency and accumulation of more saline fluid elements at the bed. The presence of this layer may explain wide discrepancies in reported dilutions near the boundary and may be environmentally important due to exposure of benthic organisms and sea grasses to high salinity. It may not persist, however, as it can be swept up by vortices that propagate radially away from the impact point. The vortices entrain ambient fluid leading to increased dilution, but they eventually collapse under their self-induced density stratification, marking the end of the near field.