Core Development

OpenFOAM provides an ideal development environment for high-end physics modelling, relying on the underlying classes providing discretisation of space and time, FVM and FEM solvers, mesh handling, I/O and database functionality. One of the most demanding jobs in the project is working on the core classes, allowing for various and ease of implementation. The list below summarises the collaborative work-in-progress led by Dr. sc. Hrvoje Jasak of Wikki Ltd., author and chief architect of OpenFOAM, in collaboration with various University research groups and commercial companies.

Fluid Structure Interaction

Doing fluid-structure interaction simulations in OpenFOAM is considerably easier than using other solvers: both fluid and structure are simulated in the same software side by side. Mapping, coupling and contact detection are built as a toolkit and can be configured to fit the coupling requirements. Run-time selection in fluid-structure interaction code allows the user to dynamically choose the physical model on either side. For example, fluid-structure interaction is algorithmically identical for incompressible laminar flow, multi-phase, free surface etc: this is mirrored in the coupling algorithm.

The example below shows oscillation of an elastic pipe under a flow pulse (please click the image for animation). Note how the flow pattern in the pipe changes as a result of combined pulsing and straightening of the pipe wall. For more details on implementation and capabilities, please contact Wikki Ltd.

FSI-solid FSI-fluid

Automatic mesh motion is the final part of the puzzle. On the structures side, a large deformation stress analysis solver naturally includes mesh motion. On the fluids side, only boundary motion is given. Here, the automatic mesh motion solver with polyhedral mesh support available in OpenFOAM provides a solution. Boundary motion is used in a FEM-type solver to calculate point motion for all mesh points, while preserving mesh spacing and quality.

Engine simulation in OpenFOAM

For realistic combustion simulations in internal combustion engines, it is necessary to simulate the flow during the exhaust and intake stroke. Intake conditions control the level and distribution of turbulence, as well as potential fuel-air mixing, with critical impact on the combustion phase. CFD modelling of intake and exhaust stroke requires handling the valve action, including opening and closing and at the same time preserving sufficient mesh quality in the critical valve region.

Example of topological changes in action during the exhaust stroke of a Diesel engine show how a combination of topological modifiers work together in a 3-D geometry with a flow solution. Away from top dead centre, the mesh is modified using mesh layering. At the end of exhaust or during combustion, increased mesh resolution is achieved by deforming the mesh.

Engine intake stroke
Engine intake stroke
Engine intake stroke

Valve action

A combination of topology modifiers recently implemented in OpenFOAM allows me to model the valve action using a combination of several layer addition/removal surfaces and sliding interfaces for each valve. The first series of pictures shows the mesh modifiers in action during the exhaust and intake strokes. Note a change in the number of cells in the cylinder and above and below the valves in motion.

Valve action Valve action
Valve action Valve action
Valve action Valve action

In-cylinder flow

A finer mesh has been chosen to simulate the flow field during the exhaust and intake stroke. The work continues in collaboration with Dr. Gianluca d'Errico and Tommaso Lucchini of the Internal Combustion Engine Group, Dipartimento di Energetica, Politecnico di Milano, Italy.

Valve action Valve action
Valve action Valve action
Valve action Valve action

Free surface flow modelling

Topological changes in OpenFOAM

Numerics and OpenFOAM

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