Oliver F. Oxtoby

A matrix-free, implicit, incompressible fractional-step algorithm for fluid-structure interaction applications

In this paper we detail a fast, fully-coupled, partitioned fluid-structure interaction (FSI) scheme. For the incompressible fluid, new fractional-step algorithms are proposed which make possible the fully implicit, but matrix-free, parallel solution of the entire coupled fluid-solid system. These algorithms include artificial compressibility pressure-poisson solution in conjunction with upwind velocity stabilisation, as well as simplified pressure stabilisation for improved computational efficiency. A dual-timestepping approach is proposed where a Jacobi method is employed for the momentum equations while the pressures are concurrently solved via a matrix-free preconditioned GMRES methodology. This enables efficient sub-iteration level coupling between the fluid and solid domains. Parallelisation is effected for distributed-memory systems. The accuracy and efficiency of the developed technology is evaluated by application to benchmark problems from the literature. The new schemes are shown to be efficient and robust, with the developed preconditioned GMRES solver furnishing speed-ups ranging between 50 and 80.

A weakly compressible free-surface flow solver for liquid-gas systems using the volume-of-fluid approach

This paper presents a weakly compressible volume-of-fluid formulation for modelling immiscible high density ratio two-fluid flow under low Mach number conditions. This follows findings of experimental analyses that concluded the compressibility of the gas has a noteworthy effect on predicted pressure loads in liquid-gas flow in certain instances. With the aim of providing a more accurate numerical representation of dynamic two-fluid flow, the solver is subsequently extended to account for variations in gas densities. A set of governing equations is proposed, which accounts for the compressible properties of the gas phase in a manner which allows for a computationally efficient numerical simulation. Furthermore, the governing equations are numerically expressed so that they allow for large variations in the material properties, without introducing notable non-physical oscillations over the interface. For the discretisation of the governing equations an edge-based vertex-centred finite volume approach is followed. The developed solver is applied to various test cases and demonstrated to be efficient and accurate.

Multi-scale simulation of droplet–droplet interaction and coalescence

Copyright: 2018 Elsevier. Due to copyright restrictions, the attached PDF file contains the pre-print version of the published item. For access to the published version, please consult the publishers website.

Modelling dynamic liquid-gas systems: Extensions to the volume-of-fluid solver

This study presents the extension of the volume-of-fluid solver, interFoam, for improved accuracy and efficiency when modelling dynamic liquid-gas systems. Examples of these include the transportation of liquids, such as in the case of fuel carried onboard air- and spacecraft or liquid natural gas on tankers. As part of the development three extensions are considered: Firstly, a revised surface capturing formulation is proposed; secondly, a new weakly compressible volume-of-fluid formulation is presented; and lastly, a piecewise-linear interpolation of the pressure derivative is implemented. For the evaluation of this solver, a number of test cases with dynamic liquid-gas flows are considered where the results are compared with experimental measurements as well as numerical predictions from the current interFoam solver .

An interactive boundary layer modelling methodology for aerodynamic flows

Purpose – The purpose of this paper is to introduce a unique technique to couple the two-integral boundary layer solutions to a generic inviscid solver in an iterative fashion. Design/methodology/approach – The boundary layer solution is obtained using the two-integral method to solve displacement thickness point by point with a local Newton method, at a fraction of the cost of a conventional mesh-based, full viscous solution. The boundary layer solution is coupled with an existing inviscid solver. Coupling occurs by moving the wall to a streamline at the computed boundary layer thickness and treating it as a slip boundary, then solving the flow again and iterating. The Goldstein singularity present when solving boundary layer equations is overcome by solving an auxiliary velocity equation along with the displacement thickness. Findings – The proposed method obtained favourable results when compared with the analytical solutions for flat and inclined plates. Further, it was applied to modelling the flow a...