enGrid: Open-Source Pre-Processing

enGrid: Open-Source Pre-Processing

enGits GmbH – Hauptstraße 20 – 79674 TodtnauDeutschland / Germany / Allemagne

http://[email protected]

Fifth OpenFOAM® Workshop

June 21-24 2010

Gothenburg

Sweden

(OPENFOAM® is a registered trade mark of OpenCFD Limited)

Oliver Gloth


Fifth OpenFOAM Workshop, June 21-24 2010, Gothenburg, Sweden page 2

OverviewOverview

• Motivation and state

• Detailed example

• General an-isotropic layers/refinement

• A few showcase examples

• Future developments

– What is planned?

– What is envisaged?

Oliver Gloth



Motivation for Open-Source MeshingMotivation for Open-Source Meshing

• enGits started in October 2006

– Main activity: software development for very specific CFD problems

– To extend business a reliable CFD solution was desired

• Commercial codes too expensive

(no guaranteed business coming in)

• Open-source, as well as in-house, solver and post-processing available

• Meshing situation not sufficient for commercial CFD work

• Expertise and a few ideas on how to improve unstructured

mesh generation

– Write own meshing software …

Oliver Gloth



Motivation for Open-Source MeshingMotivation for Open-Source Meshing

• Open-source or proprietary software?

• Decision was made rather quickly in favour of OSS

• As a small company it would be extremely difficult to

compete with the commercial codes

• Funding available for an open-source development(funded by the European Space Agency)

• Possibility to generate business with support and

customisation of the software

Oliver Gloth



open-source „process chain“open-source „process chain“● geometry modelling

● Blender

● Salome

● geometry import and surface meshing

● Gmsh

● NETGEN

● isentropic volume meshing (tetras)

● NETGEN

● Tetgen → ATTENTION: not allowed for commercial applications, NOT OPEN-SOURCE

● an-isotropic boundary layer grids

● … → enGrid

● solver

● OpenFOAM

● Code Saturne

● Elmer

● visualisation

● ParaView

● Open Data Explorer

Oliver Gloth



Current Status of ENGRIDCurrent Status of ENGRID

• Capable to create unstructured hybrid grids for CFD (prisms & tetras)

• Reliable support for prismatic boundary layers

• Requires a triangulated surface (not a proper surface mesh) as input

– STL files like for snappyHexMesh

– NETGEN could be used as IGES/STEP → STL converter

• Exports OpenFOAM cases (native format)

• Experimental support for polyhedral grids

• Basic modification tools (e.g. extrusion, rotation)

Oliver Gloth



OverviewOverview








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Example: wing with NACA0012 profile (Re = 1Example: wing with NACA0012 profile (Re = 1··101066))

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Geometry inside Blender with defined boundary patchesGeometry inside Blender with defined boundary patches

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Geometry inside Blender (exploded view)Geometry inside Blender (exploded view)

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Geometry inside Blender (exploded view)Geometry inside Blender (exploded view)

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Direct export from Blender to enGridDirect export from Blender to enGrid

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After import into enGridAfter import into enGrid

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Save as enGrid case file(s)Save as enGrid case file(s)

• enGrid stores two files per case:

– *.egc file with the description (patch

names, boundary conditions, volume

definitions, …)

– *.vtu file with actual grid information

(this file can be loaded into ParaView)

• It proved useful to save different

steps of the mesh generation

process.

For example:

– *_S0.egc: all definitions done

– *_S1.egc: surface meshing done

– *_S2.egc: first volume mesh

– *_S3.egc: refined boundary layer

Oliver Gloth



Select visible patchesSelect visible patches

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Zoom in to view wing onlyZoom in to view wing only

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Define boundary and solver parametersDefine boundary and solver parameters

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Define boundary (patch) typesDefine boundary (patch) types

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Assign boundary types to patchesAssign boundary types to patches

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Define solver parametersDefine solver parameters

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Enter parameters for surface meshingEnter parameters for surface meshing

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Select patches for meshing (typically all)Select patches for meshing (typically all)

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Define mesh size constraints for patchesDefine mesh size constraints for patches

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Define maximal edge size (global)Define maximal edge size (global)

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Define cell growthDefine cell growth

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Save and then save under a different nameSave and then save under a different name

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Start the surface meshingStart the surface meshing

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Watch the progress in the output windowWatch the progress in the output window

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Monitor the number of inserted and deleted nodesMonitor the number of inserted and deleted nodes

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After 5 iterations: display symmetry plane and check progressAfter 5 iterations: display symmetry plane and check progress

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After 15 iterations the mesh looks goodAfter 15 iterations the mesh looks good

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Select wall patches and volume to create prismatic boundary layer Select wall patches and volume to create prismatic boundary layer

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After a few minutes the boundary layer is readyAfter a few minutes the boundary layer is ready

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Clipping and which cell types are displayed can be controlledClipping and which cell types are displayed can be controlled

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One iteration to improve the tetra far-fieldOne iteration to improve the tetra far-field

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Mesh is ready for boundary layer refinementMesh is ready for boundary layer refinement

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Refine prismatic layerRefine prismatic layer

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Refine prismatic layerRefine prismatic layer

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Refined boundary layer meshRefined boundary layer mesh

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Export mesh to OpenFOAM caseExport mesh to OpenFOAM case

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Solver can be run from within enGridSolver can be run from within enGrid

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Solver output can be monitored in the enGrid output windowSolver output can be monitored in the enGrid output window

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Results: pressureResults: pressure

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Results: y+Results: y+

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OverviewOverview








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An-isotropic refinement

• “coloured” water is injected

into a laminar channel flow

• very low diffusive transport

(high Schmidt number)

• interface shall be captured by

refinement

Oliver Gloth



• “coloured” water is injected

into a laminar channel flow

• very low diffusive transport

(high Schmidt number)

• interface shall be captured by

refinement

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• usage of Blender as geometry tool

– definition of boundary conditions

– import/export of surface grids

• usage of, for example, iso-surfaces as meshing geometry

• improved prismatic boundary layer generation

• support for multiple volumes(e.g. for conjugate heat transfer simulations)

““Side effects” of the developmentSide effects” of the development

Oliver Gloth



Ariane-5 at max QAriane-5 at max Q(pressure)(pressure)

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Ariane-5 at max QAriane-5 at max Q(Mach number)(Mach number)

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Oliver Gloth



an-isotropic(aspect ratio 1:100)

tetras : 393,078prisms : 136,790total : 529,868

isotropic(equivalent to 1:5)

tetras : 2,243,414

isotropic(equivalent to 1:100)

tetras : 16,000,000,000

Oliver Gloth



OverviewOverview








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Tunnel ventilation

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• Time from “discussed

geometry” to “ready to run”

grid: appr. 3 hours

• Initial condition, 0.01m/s2

from left to right.

• 2 minutes of 0.05 m/s2 in y

direction

SloshingSloshing

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SloshingSloshing

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SloshingSloshing

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OverviewOverview








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Current development(use snappyHexMesh to recover bad STL geometries)

Oliver Gloth



Current development(use snappyHexMesh to recover bad STL geometries)

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• Isotropic refinement(solution based discrete refinement)

• y+ based boundary layer adaptation

• Improved export function for polyhedral grids

Future developments (funding confirmed)

Oliver Gloth



Future developments (ideas)• Automatic solution based layer generation

– unique capability

– offer problem specific adaptive meshing solutions

• Hex far-fields

– possibly interfacing with snappyHexMesh

• Scripting interface

– automatise tedious tasks

– enable automatic re-meshing with different solvers

• Include post-processing into GUI

– VTK is already used for mesh visualisation

→ implementation efforts would be manageable

– offer a “universal” interface for open-source CFD

Oliver Gloth



Thank you for your attention!Thank you for your attention!

http://engits.eu/engrid

• enGrid is licensed under GPL v3

• A number of openSUSE 11.2 live DVDs with enGrid

and OpenFOAM are available right here

• enGrid is also available on the workshop USB stick

(although a slightly older version)

Documents

enGrid: Open-Source Pre-Processing