Author(s): H. Shi; M. E. Negretti; J. Chauchat; K. Blanckaert; U. Lemmin; D. A. Barry
Linked Author(s): Ulrich Lemmin, Koen Blanckaert
Keywords: No Keywords
Abstract: Negatively buoyant river inflow into lakes and oceans often develops a three-dimensional plunging hyperpycnal current field. Recent field observations of the Rhone River plume in Lake Geneva show that the unconfined hyperpycnal river inflow spreads laterally, forming a triangular shaped pattern at the water surface before plunging. In order to improve the understanding of such an unconfined plunging process, a laboratory and a numerical study was performed. Experiments were conducted using salinity to control the density difference. A Computational Fluid Dynamics (CFD) model based on the Boussinesq assumption and Large Eddy Simulation was calibrated with the experimental results. It was found that as the hyperpycnal river inflow moves straight out into the ambient, it also sinks laterally on both sides forming a lock-exchange type secondary current, i. e., as it diverges on the both sides near the bottom, it converges towards the centreline near the water surface. As a result, a near-surface triangular pattern forms. The vertex of the surface triangle is defined as the ultimate plunge point and indicates the longitudinal distance xup that the hyperpycnal current moves before it totally plunges. It was demonstrated that the ultimate plunge point advances offshore when the initial densimetric Froude number increases. Numerical model results and field observations of the Rhone River plume agreed reasonably well with respect to the estimated location of the ultimate plunge point.
Year: 2022