The GFS Multi-Phase and Multi-Concentration Flow Solver

The GFS code is a three-dimensional, incompressible, unsteady, multi-phase and multi-concentration CFD flow solver. The full Navier-Stokes equations describing the motion of continuous and turbulent fluid media are solved numerically on  curvilinear, non-orthogonal, unstructured numerical grids. Variable and time-dependent boundary conditions can be employed. Arbitrary number of transport equations for scalar variables can be implicitly solved since it supports multi-species property libraries for various working media. Special emphasis has been given to simulation of multi-phase flow systems including phase-change phenomena. This is achieved by including into the flow conservation equations the volume fraction of each phase, as well as the mass, momentum and energy exchange source term between the mutli-phases. The available multi-phase flow models are based both on Eulerian-Lagrangian approximations describing discrete solid particles, liquid droplet and cavitation flow cases, and Eulerian-Eulerian approximations describing separated flow conditions. For the calculation of the dispersed phase volume fraction, a methodology has been developed allowing for the effect of particle sizes larger than the occupying cell to be taken into account.

The code is fully parallel and allows for any type of moving unstructured mesh that may consist of any kind of prism (hexahedral, tetrahedral e.t.c.) to be used. Therefore, both in-house and commercial grid generation software can be utilised. Adaptive local grid refinement is used in a number of cases for obtaining more accurate predictions at shorter calculation time. Spatial discretisation includes first and second order schemes with a choice of upwind differencing.  Time discretisation schemes include first order backward implicit Euler as well as the second order implicit Crank–Nicholson scheme. Turbulence can be simulated using the well-known k-epsilon, RNG k-epsilon, NEC k-epsilon, k-omega and the standard LES models.

GFS has been applied to the simulation of flows realised with internal combustion engines, various types of nozzles and environmental flows. Fundamental flows studies involving single droplet impingement processes, fuel atomisation, droplet fragmentation and vaporisation have been investigated. Browse are pages for a more detailed description of the flow models available and look to application cases.

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