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File blockMeshDict​

Lets walk through the file:
# less $FOAM_RUN /pitzDaily/system/blockMeshDict

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

OpenFOAM file header

convertToMeters 0.001;

Whole geometry scaling factor

vertices
(
    (-20.6 0 -0.5)
    (-20.6 25.4 -0.5)
    (0 -25.4 -0.5)
    (0 0 -0.5)
    (0 25.4 -0.5)
    (206 -25.4 -0.5)
    (206 0 -0.5)
    (206 25.4 -0.5)
    (290 -16.6 -0.5)
    (290 0 -0.5)
    (290 16.6 -0.5)

    (-20.6 0 0.5)
    (-20.6 25.4 0.5)
    (0 -25.4 0.5)
    (0 0 0.5)
    (0 25.4 0.5)
    (206 -25.4 0.5)
    (206 0 0.5)
    (206 25.4 0.5)
    (290 -16.6 0.5)
    (290 0 0.5)
    (290 16.6 0.5)
);

Blocks’ vertices

negY
(
    (2 4 1)
    (1 3 0.3)
);

posY
(
    (1 4 2)
    (2 3 4)
    (2 4 0.25)
);

posYR
(
    (2 1 1)
    (1 1 0.25)
);

Auxiliary settings for multi-grading functionality that we use in Blocks’ definition.

blocks
(
    hex (0 3 4 1 11 14 15 12)
    (18 30 1)
    simpleGrading (0.5 $posY 1)

    hex (2 5 6 3 13 16 17 14)
    (180 27 1)
    edgeGrading (4 4 4 4 $negY 1 1 $negY 1 1 1 1)

    hex (3 6 7 4 14 17 18 15)
    (180 30 1)
    edgeGrading (4 4 4 4 $posY $posYR $posYR $posY 1 1 1 1)

    hex (5 8 9 6 16 19 20 17)
    (25 27 1)
    simpleGrading (2.5 1 1)

    hex (6 9 10 7 17 20 21 18)
    (25 30 1)
    simpleGrading (2.5 $posYR 1)
);

Blocks’ definition

Using simpleGrading can handle cell expansion ratio for the whole block

Using edgeGrading can handle cell expansion ratio for each edge in the block independently

We decribe now how multi-grading is used. For example $posY in the first defined block (line 70) splits the block into 3 divisions in the local y-direction, representing 1/5, 2/5, 2/5 of the block length, including 4/11, 3/11, 4/11 of number of cells, and with expansion ratio 2, 4, 0.25.

The similar meaning has the same multi-grading used at line 78, but now for a single edge.

openfoam tutorial backward facing step pitzDaily block mesh

Figure: Backward-Facing-Step tutorial, blocks to setup the blockMesh example

edges           
(
);

Edge definition; if not specified otherwise, all edges are straight lines

 

boundary
(
    inlet
    {
        type patch;
        faces
        (
            (0 1 12 11)
        );
    }
    outlet
    {
        type patch;
        faces
        (
            (8 9 20 19)
            (9 10 21 20)
        );
    }
    upperWall
    {
        type wall;
        faces
        (
            (1 4 15 12)
            (4 7 18 15)
            (7 10 21 18)
        );
    }
    lowerWall
    {
        type wall;
        faces
        (
            (0 3 14 11)
            (3 2 13 14)
            (2 5 16 13)
            (5 8 19 16)
        );
    }
    frontAndBack
    {
        type empty;
        faces
        (
            (0 3 4 1)
            (2 5 6 3)
            (3 6 7 4)
            (5 8 9 6)
            (6 9 10 7)
            (11 14 15 12)
            (13 16 17 14)
            (14 17 18 15)
            (16 19 20 17)
            (17 20 21 18)
        );
    }
);

Mesh boundary definition

 

% mergePatchPairs
% (
% );
% 
% // ************************************************************************* //

Minimal and Maximal Values Options

During the computation, especially right at its start, some unphysical oscillations of solution may appear. To make the solver more robust there may be minimal and maximal values specified for selected variables. See file fvSolution.

Previous: Turbine Efficiency Up: Formulas for the Efficiency Next: Wind Turbine Efficiency
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Fan Efficiency

  • Pt    aerodynamic power, $ P_\mathrm{t} = Y_\mathrm{t} \cdot \dot{m}_2 $ [W]
  • Pw    torque power, $ P_\mathrm{w} = M_\mathrm{d} \cdot \omega $ [W]
  • f     compress factor, $ f = 1- 0.36 \cdot \frac{\Delta p_\mathrm{s}}{p_\mathrm{s1}}$ [-]
  • Yst     static work, $ Y_\mathrm{st} = f \cdot \frac{\Delta p_\mathrm{s}}{\rho^1}$ [m$ ^2$/s$ ^2$]
  • Yd    dynamic work, $ Y_\mathrm{d} = \frac{c_2^2-c_1^2}{2}$ [m$ ^2$/s$ ^2$]
  • Yt    total work, $ Y_\mathrm{t} = Y_\mathrm{st} + Y_\mathrm{d}$ [m$ ^2$/s$ ^2$]
  • psi    pressure number, $ \psi = \frac{2 \cdot D \cdot \Delta p_\mathrm{t}}{\rho_1 \cdot c_c^2} = \frac{729.5 \cdot \Delta p_\mathrm{t}}{n^2 \cdot D^2 \cdot \rho_1}$ [-]
  • phi    flow number, $ \phi = \frac{Q_w}{A \cdot c_c} = \frac{24.3 \cdot Q_w}{n \cdot D^3}$ [-]
  • axialForce    axial force on rotor, $ F_\mathrm{a}$ [N]
  • pTotInlet     total pressure at the inlet, $ p_\mathrm{t1}$ [Pa]
  • pTotVolute     total pressure at the outlet, $ p_\mathrm{t2}'$ [Pa]
  • pTotOutlet     total pressure at the wheel outlet, $ p_\mathrm{t2}$ [Pa]
  • pInlet     static pressure at the inlet, $ p_\mathrm{s1}$ [Pa]
  • pVolute     static pressure at the outlet, $ p_\mathrm{s2}'$ [Pa]
  • pOutlet     static pressure at the wheel outlet, $ p_\mathrm{s2}$ [Pa]
  • magUInlet     velocity at the inlet, $ c_1$ [m/s]
  • magUVolute     velocity at the outlet, $ c_2'$ [m/s]
  • magUOutlet     velocity at the wheel outlet, $ c_2$ [m/s]
  • massFlowInlet     mass flow at the inlet, $ \dot{m}_1$ [kg/s]
  • massFlowVolute     mass flow at the outlet, $ \dot{m}_2'$ [kg/s]
  • massFlowOutlet     mass flow at the wheel outlet, $ \dot{m}_2$ [kg/s]
  • rhoInlet     density at the inlet, $ \rho_1$ [kg/m$ ^3$]
  • rhoVolute         density at the outlet, $ \rho_2'$ [kg/m$ ^3$]
  • rhoOutlet     density at the wheel outlet, $ \rho_2$ [kg/m$ ^3$]
  • volumeFlowRateInlet     volumetric flow rate at the inlet, $ Q_\mathrm{w1}$ [m$ ^3$/s]
  • volumeFlowRateVolute     volumetric flow rate at the outlet, $ Q_\mathrm{w2}'$ [m$ ^3$/s]
  • volumeFlowRateOutlet     volumetric flow rate at the wheel outlet, $ Q_\mathrm{w2}$ [m$ ^3$/s]
  • moment     torque at wheel, $ M_\mathrm{d}$ [N$ \cdot$m]
  • totalPressureDifference     difference in total pressure inlet-outlet, $ \Delta p_\mathrm{t}$ [Pa]
  • staticPressureDifference     difference in static pressure inlet-outlet, $ \Delta p_\mathrm{s}$ [Pa]