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

Abstract

Abstract. High resolution direct numerical simulations (DNS) are an important tool for the detailed analysis of turbidity current dynamics. Models that resolve the vertical structure and turbulence of the flow are typically based upon the Navier–Stokes equations. Two-dimensional simulations are known to produce unrealistic cohesive vortices that are not representative of the real three-dimensional physics. The effect of this phenomena is particularly apparent in the later stages of flow propagation. The ideal solution to this problem is to run the simulation in three dimensions but this is computationally expensive. This paper presents a novel finite-element (FE) DNS turbidity current model that has been built within Fluidity, an open source, general purpose, computational fluid dynamics code. The model is validated through re-creation of a lock release density current at a Grashof number of 5 × 106 in two, and three-dimensions. Validation of the model considers the flow energy budget, sedimentation rate, head speed, wall normal velocity profiles and the final deposit. Conservation of energy in particular is found to be a good metric for measuring mesh performance in capturing the range of dynamics. FE models scale well over many thousands of processors and do not impose restrictions on domain shape, but they are computationally expensive. Use of discontinuous discretisations and adaptive unstructured meshing technologies, which reduce the required element count by approximately two orders of magnitude, results in high resolution DNS models of turbidity currents at a fraction of the cost of traditional FE models. The benefits of this technique will enable simulation of turbidity currents in complex and large domains where DNS modelling was previously unachievable.

A new methodology for performing large scale simulations of tsunami generated by deformable submarine slides

“…It has been used in a number of fluid flow studies, ranging from laboratory to ocean-scale (e.g. Wells et al, 2010;Hill et al, 2012;Hiester et al, 2011;Parkinson et al, 2014). In an ocean modelling context, Fluidity has been used to model both modern and ancient earthquake-generated tsunami (Oishi et al, 2013;Mitchell et al, 2010;Shaw et al, 2008), and tsunami generated by three-dimensional rigid-block submarine slides with prescribed motion, in a study of the ancient Storegga Slide (Hill et al, 2014).…”

Numerical simulation of scour below pipelines using flexible mesh methods

“…Fluidity 2015, an open source, general purpose computational fluid dynamics FEM code developed at Imperial College London (Piggott et al 2008), has the capabilities of solving the N-S equations with sufficiently fine meshes (adaptive remeshing) and sufficiently small time steps (adaptive time stepping) to resolve with at great resolution the eddies and fluctuations in small-scale turbulence models (Parkinson et al 2014). Although this is theoretically possible, for many engineering applications it is not always necessary to resolve all details of the turbulence fluctuations in a simulation, and some form of parametrisation is required.…”

A conservative, physically compatible, dual-field discretization for turbidity currents: with application to the lock-exchange problem

“…First, because they are known to be an important contributor to the formation of deep sea oil reservoirs [8]. Second, due to their significant destructive power they are one of the main hazards to submarine telecommunication cables and pipelines [3,9].…”

“…Small-scale laboratory experiments are a good alternative that provides much understanding into the dynamics of turbidity currents. Unfortunately, they have limitations due to scaling constraints and existing measurement techniques [9,10]. Another approach used in the study of gravity currents in general and turbidity currents in particular is modelling.…”