Numerical Simulation and Experimental Investigation of 3-Dimensional Confined Density Currents

Dense underflows are continuous currents which move down-slope due to the fact that their density is greater than that of ambient water. In this work, 2-D and 3-D steady-state salt solution density currents are investigated by means of a set of experimental studies and the data used to verify the numerical model. In the laboratory experiments, the density current enters the channel via a sluice gate into a lighter ambient fluid and moves forward down-slope. The velocity components are measured using Acoustic Doppler Velocimeters (ADVs). The thickness in the vertical direction of the density current layer is also measured. In the numerical simulation, a low-Reynolds number turbulent model (Launder and Sharma, 1974) is applied to simulate the structure of the 3-D density current. Then, by reducing the width of the 3-D channel (referred to as a confined density current) we show that the height and stream-wise velocity of a density current increase considerably in comparison with those of an unconfined current. For verification, the results of the unconfined channel are compared with the 3-D experimental data, as are the height and velocity profiles of the confined current. It seems that decreasing the width and confining the density currents provide the conditions for minimizing sediment deposition and the sedimentation rates can be greatly reduced if the current is particle-laden. Although the k-ɛ Launder and Sharma model is applied here to a conservative salt solution density current, it seems that the analysis can be valid in general for turbidity currents laden with fine particles.