摘要:摩托車空氣動力、車輛、三維、多面體、OPENFOAM

項(xiàng)目概述

該項(xiàng)目模擬了摩托車空氣動力特性

隨著摩托車的普及,摩托車速度的提高及國內(nèi)摩托車賽車運(yùn)動的開展,摩托車的空氣動力特性也越來越應(yīng)該引起人們的重視。安全、節(jié)能和環(huán)保等方面的法規(guī)和標(biāo)準(zhǔn)給摩托車設(shè)計(jì)提出了更高的要求,而摩托車空氣動力學(xué)的研究對安全、節(jié)能和環(huán)保方面具有重要的意義。

模型簡化

本算例使用幾何來源openfoam標(biāo)準(zhǔn)案例庫，幾何模型如圖1所示。

1. 摩托車簡化幾何

網(wǎng)格設(shè)置

本算例采用snappyHexMesh對幾何模型進(jìn)行網(wǎng)格劃分（如圖2），詳細(xì)參數(shù)設(shè)置如下所示：

geometry

{motorBike

{type triSurfaceMesh;

file "motorBike.obj";}

refinementBox

{type searchableBox;

min (-1.0 -0.7 0.0);

max ( 8.0 0.7 2.5);

}

};

castellatedMeshControls

{maxLocalCells 1000000;

maxGlobalCells 2000000;

minRefinementCells 1;

maxLoadUnbalance 0.20;

nCellsBetweenLevels 3;

features

(

{file "motorBike.eMesh";

level 7;}

);

refinementSurfaces

{motorBike

{level (6 7);

patchInfo

{type wall;

inGroups (motorBikeGroup);

}

}

}

resolveFeatureAngle 30;

refinementRegions

{refinementBox

{mode inside;

levels ((1E15 4));}

}

locationInMesh (3.0001 3.0001 0.43);

allowFreeStandingZoneFaces true;}

snapControls

{nSmoothPatch 3;

tolerance 1.0;

nSolveIter 100;

nRelaxIter 5;

nFeatureSnapIter 10;

implicitFeatureSnap false;

explicitFeatureSnap true;

multiRegionFeatureSnap false;}

addLayersControls

{relativeSizes true;

layers

{"(lowerWall|motorBike).*"

{nSurfaceLayers 1;}

}

expansionRatio 1.0;

finalLayerThickness 0.3;

minThickness 0.1;

nGrow 0;

featureAngle 60;

slipFeatureAngle 30;

nRelaxIter 5;

nSmoothSurfaceNormals 1;

nSmoothNormals 3;

nSmoothThickness 10;

maxFaceThicknessRatio 0.5;

maxThicknessToMedialRatio 0.3;

minMedianAxisAngle 90;

nBufferCellsNoExtrude 0;

nLayerIter 50;}

meshQualityControls

{#include "meshQualityDict"

nSmoothScale 4;

errorReduction 0.75;}

writeFlags

(scalarLevels

layerSets

layerFields // write volScalarField for layer coverage);

mergeTolerance 1e-6;

1. 摩托車網(wǎng)格模型

網(wǎng)格信息參數(shù)及網(wǎng)格質(zhì)量參數(shù)如表1所示：

表1網(wǎng)格信息參數(shù)

網(wǎng)格總數(shù)

---

數(shù)量 1196949 3181450 1003349 
網(wǎng)格類型 
類型 hexahedra prisms tet wedges polyhedra 數(shù)量 826038 30823 5599 136301 網(wǎng)格質(zhì)量 
評價指標(biāo) 最大縱橫比 最小體積 最大非正交性 最大歪斜率 值 38.7 1.79e-009. 64.98 5.97

邊界條件參數(shù)

該算例湍流模型選用K-Omega SST模型。邊界條件見表1

表1 邊界條件參數(shù)

邊界條件 參數(shù)

---

速度進(jìn)口 20m/s 壓力出口 0Pa

求解器參數(shù)設(shè)置

fvSchemes設(shè)置

ddtSchemes

{default steadyState;}

gradSchemes

{default Gauss linear;

grad(U) cellLimited Gauss linear 1;}

divSchemes

{default none;

div(phi,U) bounded Gauss linearUpwindV grad(U);

div(phi,k) bounded Gauss upwind;

div(phi,omega) bounded Gauss upwind;

div((nuEff*dev2(T(grad(U))))) Gauss linear;}

laplacianSchemes

{default Gauss linear corrected;}

interpolationSchemes

{default linear;}

snGradSchemes

{default corrected;

}

wallDist

{method meshWave;

}

fvSolution設(shè)置

solvers

{p

{solver GAMG;

smoother GaussSeidel;

tolerance 1e-7;

relTol 0.01;

}

Phi

{$p;

}

U

{solver smoothSolver;

smoother GaussSeidel;

tolerance 1e-8;

relTol 0.1;

nSweeps 1;

}

k

{solver smoothSolver;

smoother GaussSeidel;

tolerance 1e-8;

relTol 0.1;

nSweeps 1;

}

omega

{solver smoothSolver;

smoother GaussSeidel;

tolerance 1e-8;

relTol 0.1;

nSweeps 1;

}

}

SIMPLE

{nNonOrthogonalCorrectors 0;

consistent yes;

}

potentialFlow

{nNonOrthogonalCorrectors 10;

}relaxationFactors

{equations

{U 0.9;

k 0.7;

omega 0.7;}

}

cache

{grad(U);}

controlDict設(shè)置

application simpleFoam;

startFrom latestTime;

startTime 0;

stopAt endTime;

endTime 500;

deltaT 1;

writeControl timeStep;

writeInterval 100;

purgeWrite 0;

writeFormat binary;

writePrecision 6;

writeCompression uncompressed;

timeFormat general;

timePrecision 6;

runTimeModifiable true;

functions

{#include "streamLines"

#include "cuttingPlane"

#include "forceCoeffs"}

計(jì)算結(jié)果

本算例計(jì)算總步長為500步，計(jì)算速度流線、壓力云圖如下所示：