THREE-DIMENSIONAL STRUCTURES IN EXPERIMENTAL DENSITY CURRENTS

摘要

Density currents are continuous currents which move down-slope due to the fact that their density is greater than that of ambient water. The density difference is caused by temperature differences, chemical elements, dissolved materials, or suspended sediment. Many researchers have studied the density current structures, their complexities and uncertainties. However, there is not a detailed 3-D turbulent density current data set perfectly. In this work, the structure of 3-dimensional salt solution density currents is investigated. A laboratory channel was used to study the flow resulting from the release of salt solution into freshwater over an inclined bed. The experiments were conducted with different bottom slopes, inlet concentrations and flow rates. In these tests, the instantaneous velocities are measured by an ADV apparatus (Acoustic Doppler Velocimeter). Results show that by increasing the bed-slope and inlet concentrations, the height of the current decreases. As the density current moves downward the channel or by increasing the discharge, the height of the density current increases. Finally, the effects of different variables such as the bed slope, concentration and flow rate of entering fluid on the velocity profile in different distances from the entrance is studied. The entrainment coefficient, lateral spreading and drag coefficient of the bed and shear layer between salt solution and ambient water is discussed.