Nerdalytics

Wednesday, July 15, 2015

Arduino with relay to control fan

Calculate inlet conditions for k-epsilon

How to estimate k and epsilon for inlet

k=1.5*(I*U)^2
where I is turbulence intensity and U is velocity, k is turbulent kinetic energy

epsilon=C_mu^0.75*k^1.5/L
where C_mu=0.09, epsilon is dissipation rate, L is the mixing length

for OpenFOAM easy conditions to specify are

turbulentIntensityKineticEnergyInlet for k

inlet
    {
        type            turbulentIntensityKineticEnergyInlet;
        intensity            0.05 ;
        value           uniform .05; //dummy value
    }

turbulentMixingLengthDissipationRateInlet for epsilon

inlet
    {
        type            turbulentMixingLengthDissipationRateInlet;
        mixingLength            0.01; //m
        value          uniform 0.01; // dummy
    }

see description by ESI
or https://en.wikipedia.org/wiki/Turbulence_kinetic_energy
http://www.cfd-online.com/Wiki/Turbulence_free-stream_boundary_conditions

Friday, July 10, 2015

How to use topoSet to generate a circular inlet patch with OpenFOAM

Allrun script

#!/bin/sh
cd ${0%/*} || exit 1    # run from this directory

# Source tutorial run functions
. $WM_PROJECT_DIR/bin/tools/RunFunctions

   rm log.*
   rm 0 -r
   cp 0.org 0 -r
    # And execute
    runApplication blockMesh

    runApplication topoSet
    runApplication createPatch -overwrite

    runApplication decomposePar -force
    runParallel `getApplication` 4
    runApplication reconstructPar

# ----------------------------------------------------------------- end-of-file

topoSetDict

createPatchDict

/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      / F ield         | OpenFOAM: The Open Source CFD Toolbox           |
| \\    /   O peration     | Version: 2.3.1                                 |
|   \\ /    A nd           | Web:      www.OpenFOAM.org                      |
|    \\/     M anipulation |                                                 |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       dictionary;
    object      createPatchDict;
}

// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

// This application/dictionary controls:
// - optional: create new patches from boundary faces (either given as
//   a set of patches or as a faceSet)
// - always: order faces on coupled patches such that they are opposite. This
//   is done for all coupled faces, not just for any patches created.
// - optional: synchronise points on coupled patches.

// 1. Create cyclic:
// - specify where the faces should come from
// - specify the type of cyclic. If a rotational specify the rotationAxis
//   and centre to make matching easier
// - always create both halves in one invocation with correct 'neighbourPatch'
//   setting.
// - optionally pointSync true to guarantee points to line up.

// 2. Correct incorrect cyclic:
// This will usually fail upon loading:
// "face 0 area does not match neighbour 2 by 0.0100005%"
// " -- possible face ordering problem."
// - in polyMesh/boundary file:
//      - loosen matchTolerance of all cyclics to get case to load
//      - or change patch type from 'cyclic' to 'patch'
//        and regenerate cyclic as above

// Do a synchronisation of coupled points after creation of any patches.
// Note: this does not work with points that are on multiple coupled patches
//       with transformations (i.e. cyclics).
pointSync false;

// Patches to create.
patches
(
    {
        // Name of new patch
        name inlet;

        // Type of new patch
        patchInfo
        {
            type patch;
        }

        // How to construct: either from 'patches' or 'set'
        constructFrom set;

        // If constructFrom = patches : names of patches. Wildcards allowed.
        patches ("periodic.*");

        // If constructFrom = set : name of faceSet
        set f0;
    }
);

// ************************************************************************* //

How to automate renaming of STL patches without Salome using only OpenFOAM surface utilities and a script

This describes how to automate naming of patches of the stl file without using Salome or other software but with native OpenFOAM tools and a bash script. This is for use with cfMesh but a similar approach could be used with snappyHexMesh.

Allmesh Script

#!/bin/sh
cd ${0%/*} || exit 1 # run from this directory

# Source tutorial run functions
. $WM_PROJECT_DIR/bin/tools/RunFunctions

rm log.*
rm -r input
rm -r output
mkdir input
mkdir output

# split stl into inlet and walls
runApplication surfaceSubset system/surfaceSubsetDictInlet constant/triSurface/input.stl input/inlet.stl

mv log.surfaceSubset log.surfaceSubsetInlet

runApplication surfaceSubset system/surfaceSubsetDictRInlet constant/triSurface/input.stl input/walls.stl

mv log.surfaceSubset log.surfaceSubsetInletR

# split walls into outlet and walls
runApplication surfaceSubset system/surfaceSubsetDictOutlet input/walls.stl input/outlet.stl

mv log.surfaceSubset log.surfaceSubsetInletROutlet

runApplication surfaceSubset system/surfaceSubsetDictROutlet input/walls.stl input/walls.stl

mv log.surfaceSubset log.surfaceSubsetInletROutletR

# combine files
../../scripts/./stlCombine input output

#generate fms file with edges but retaining patches
runApplication surfaceFeatureEdges output/mergedStl.stl output/elbow.fms -angle 45

#generate mesh
runApplication cartesianMesh

#change definitions of patches
runApplication changeDictionary

surfaceSubsetDictInlet file

/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      / F ield         | OpenFOAM: The Open Source CFD Toolbox           |
| \\    /   O peration     | Version: 2.4.0                                 |
|   \\ /    A nd           | Web:      www.OpenFOAM.org                      |
|    \\/     M anipulation |                                                 |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       dictionary;
    object      surfaceSubsetDict;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

// Select triangles by label
faces ();//#include "badFaces";

// Select triangles using given points (local point numbering)
localPoints ( );

// Select triangles using given edges
edges ();

// Select triangles (with face centre) inside box
zone
(
    (.507 .25 -.101)
    (.509 .36 .101)
);

// Select triangles (with face centre) inside or outside of another surface.
// (always selects triangles that are 'on' other surface)
/*
surface
{
    name "sphere.stl";
    outside     yes;
}

// Select triangles on plane
plane
{
    planeType embeddedPoints;
    embeddedPointsDict
    {
        //point1 (-937.259845440205 160.865349115986 240.738791238078);
        //point2 (-934.767379895778 9.63875523747379 14.412359671298);
        //point3 (44.4744688899417 121.852927962709 182.352485273106);
        point1 (-957.895294591874 242.865936478961 162.286611511875);
        point2 (-961.43140327772 4.53895551562943 3.04159982093444);
        point3 (91.2414146173805 72.1504381996692 48.2181961945329);
    }

    // Distance from plane
    distance 0.1;
    // Normal difference to plane
    cosAngle 0.99;
}
*/

// Extend selection with edge neighbours
addFaceNeighbours no;

// Invert selection
invertSelection false;

// ************************************************************************* //

surfaceSubsetDictInletR change invertSelection true;

surfaceSubsetDictOutlet change coordinates of

box;surfaceSubsetDictOutletR change invertSelection true;

stlCombine code from Kruno at

https://openfoamwiki.net/index.php/Thread:Talk:Sig_Numerical_Optimization/Salome_and_cfMesh_parametrization

meshDict for cfMesh

/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                |
| \\      / F ield         | cfMesh: A library for mesh generation          |
| \\    /   O peration     |                                                |
|   \\ /    A nd           | Author: Franjo Juretic                         |
|    \\/     M anipulation | E-mail: franjo.juretic@c-fields.com            |
\*---------------------------------------------------------------------------*/

FoamFile
{
    version   2.0;
    format    ascii;
    class     dictionary;
    location "system";
    object    meshDict;
}

// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

surfaceFile "output/elbow.fms";

maxCellSize .05;

boundaryCellSize .0049;

minCellSize .0049;

localRefinement
{
    walls
    {
        cellSize 0.0025;
    }
}

boundaryLayers
{
    nLayers 1;

    thicknessRatio 1.1;

    maxFirstLayerThickness 0.003;

    patchBoundaryLayers
    {
      "walls.*"
        {
            nLayers           3;

            thicknessRatio    1.2;

            maxFirstLayerThickness .005;

            allowDiscontinuity 0;
        }

    }
}

/*
renameBoundary
{
    defaultName        junk;
    defaultType        wall;

    newPatchNames
    {
        "inl.*"
        {
            newName     testo;
            newType     patch;
        }

    }
}*/


// ************************************************************************* //

changeDictionaryDict

Wednesday, July 8, 2015

Arduino thermocouple

I hooked up a thermocouple to Arduino

Saturday, March 22, 2014

Here is the acrylic tank that I built in action. I shoot an air jet from my air compressor into the tank.

Saturday, March 1, 2014

Side view of air jet from converging nozzle into a bucket of water

This is the same as the jet from the converging nozzle but is viewed from the side. I cut out part of the bucket and replaced it with polycarbonate. It is played back in full in real time and then 32 times slower for the first part of the video.