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Initial dilution of a horizontal jet in a strong current

University of British Columbia

The initial dilution of waste discharging into a water body can be accomplished by turbulent jets. Enhanced mixing is thought to occur when the water body is a river, due to the presence of an ambient current and increased turbulence levels. One case of jet mixing in a river is when the jet is weak compared with the ambient current, such as a pulp mill discharge into the Fraser River. This research was initially driven by the need to model the interaction between suspended sediments and pulp mill effluent in the Fraser River Basin under the Fraser River Action Plan. Because of the detrimental effect on water quality, researchers are investigating the physical, chemical and biological processes which occur when an effluent plume is discharged into the river. This study examines the physical mechanisms which are responsible for mixing in the vicinity of the discharge. To investigate the mixing process in the initial near-field, experiments involving a single buoyant jet discharging at an angle of 45 degrees into a moving ambient environment were performed. The main emphasis of this study is on using temperature measurements to calculate dilution in the vicinity of the port. To simulate field conditions in the laboratory, the range of two modelling parameters were preserved, namely the densimetric jet Froude number and the velocity ratio, which is the ratio of jet velocity to ambient velocity. The experimental data showed that the velocity ratio has a greater influence on dilution than the jet Froude number. Generally, dilution increases with decreasing velocity ratio or increasing ambient current. The data correspond well with previous studies on dilution of jet in a perpendicular crossflow. Bottom attachment of the jet is evident, creating a possible mechanism for entrainment of bottom sediments into the effluent plume in relation to the Fraser River.

Thesis/Dissertation

application/pdf

2009-02-16

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http://hdl.handle.net/2429/4621

Civil Engineering

University of British Columbia

UBCV

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