3D numerical modelling of turbidity currents

Abstract

During floods, the density of river water usually increases due to a subsequent increase in the concentration of the suspended sediment that the river carries, causing the river to plunge underneath the free surface of a receiving water basin and form a turbidity current that continues to flow along the bottom. The study and understanding of such complex phenomena is of great importance, as they constitute one of the major mechanisms for suspended sediment transport from rivers into oceans, lakes or reservoirs. Unlike most of the previous numerical investigations on turbidity currents, in this paper, a 3D numerical model that simulates the dynamics and flow structure of turbidity currents, through a multiphase flow approach is proposed, using the commercial CFD code FLUENT. A series of numerical simulations that reproduce particular published laboratory flows are presented. The detailed qualitative and quantitative comparison of numerical with laboratory results indicates that apart from the global flow structure, the proposed numerical approach efficiently predicts various important aspects of turbidity current flows, such as the effect of suspended sediment mixture composition in the temporal and spatial evolution of the simulated currents, the interaction of turbidity currents with loose sediment bottom layers and the formation of internal hydraulic jumps. Furthermore, various extreme cases among the numerical runs considered are further analyzed, in order to identify the importance of various controlling flow parameters.

Direct numerical simulations of particle-laden density currents with adaptive, discontinuous finite elements

“…This paper simulates a lock release density current at a Grashof number of 5 × 10 6 in two and three dimensions with a configuration similar to that of Necker et al (2002). The governing equations are well established and have been validated extensively against experimental data across a range of simulation configurations (Sequeiros et al, 2009;Necker et al, 2002;Espath et al, 2014;Huang et al, 2007;Georgoulas et al, 2010). This paper validates the use of novel computational methods, including unstructured mesh adaptivity and discontinuous finite elements, through convergence analyses and by direct comparison with the results from the previous models of Necker et al (2002) and Espath et al (2014), providing a framework for future modelling efforts of this type.…”

Water quality monitoring and modeling in Lagoon Jusan, Japan

“…The governing equations are solved sequentially using the control volume method. The equations and the solution procedure are presented and discussed in detail, in the work Georgoulas et al (2009). Therefore, due to space limitations, these equations are not presented here.…”

“…lished laboratory experiments on hyperpycnal particulate currents, in the work of Georgoulas et al (2009). Finally, an additional series of numerical runs are conducted in order to further validate the numerical model, by checking its ability in capturing the critical suspended sediment concentration for the transition from hypopycnal to hyperpycnal particulate currents.…”

Numerical investigation of continuous, high density turbidity currents response, in the variation of fundamental flow controlling parameters

“…However most of these previous works treat turbidity currents with a quasi-single-phase approach, solving one set of continuity and momentum equations for the ambient fluid and treating the transport of sediment particles through an advection-diffusion equation for sediment concentration. According to the authors' best knowledge, the first numerical effort that treats turbidity current flows through a multi-phase approach, assuming that the sediment-laden turbidity current flow consists of separate solid and fluid phases, is the recent work by Georgoulas et al (2010) [1]. In the proposed work a separate velocity field is calculated for each phase (water and sediment classes), since the laws for the conservation of mass and momentum are modified accordingly in order to be satisfied by each phase individually.…”

“…In the present paper, the multiphase numerical approach that is validated in the work of Georgoulas et al (2010) [1], is further applied in order to investigate the exact qualitative and quantitative effect of fundamental flow controlling parameters, such as bed slope and roughness, initial suspended sediment concentration and diameter, in the hydrodynamic and depositional characteristics of continuous, high density turbidity currents. For this purpose, four different series of parametric numerical experiments are conducted, using a laboratory scale experimental set-up, similar to the one used in the laboratory experiments of Baas et al (2004) [12].…”