Three-Dimensional Modeling of Density Current in Confined and Unconfined Channels

Abstract

Dense underflows are continuous currents which move down-slope due to the fact that their density is heavier than that ambient water. In this work, 2-D and 3-D density current in a channel were investigated by a set of experimental studies and the data were used to simulate the density current. The velocity components were measured using Acoustic Doppler Velocimetry (ADV). The height of density current (current's depth) was also measured. In this study, the density current with a uniform velocity and concentration enters the channel via a sluice gate into a lighter ambient fluid and moves forward down-slope. A low-Reynolds number turbulent model (Launder and Sharma, 1974) has been applied to simulate the structure of 3-D density current in the confined (small width three dimensional density current) and unconfined (large width three dimensional density current) channels. The computed velocity profiles in unconfined channel were compared with the 3-D experimental data for verification. The height and velocity profiles of the confined current were also compared with 2-D experimental data. It was shown that by decreasing in width of the channel, the height of the current and the magnitude of maximum and average velocity increase and the confined current behaves as 2-D current after a distance. These factors prepare the conditions for minimizing sediment deposition and sedimentation rates can be greatly reduced. Although the k - ε Launder and Sharma model is applied here to a conservative density current, it seems that the analysis can be valid in general for turbidity current laden with fine particles.