How can I get the pressure gradient along the direction normal to the local wall surface

qtian · January 14, 2008, 16:28

Hello,

Can anyone tell me how to the pressure gradient normal to the local wall surface? I have caculated pressure gradient at the first node away from surface. However, I don't know how to get the information of local normal vectors to the wall. Thanks

eugene · January 18, 2008, 06:29

p.boundaryField()[patchID].snGrad();

Which is generally zero for walls.

You seem to want to extrapolate the pressure gradient. To do this you will need:

volVectorField gradp = fvc::grad(p);
vectorField nearSurfaceGradP = gradp.boundaryField()[patchID].patchInternalField();

const vectorField& surfaceNormal = mesh.boundary()[patchID].nf();

scalarField gradpWallNormal = nearSurfaceGradP & surfaceNormal;

kerstin · November 17, 2008, 08:11

Hi all,

I tried this code above to calculate the gradient of a tensor component in normal direction to the wall...

label wallPatchID = mesh.boundaryMesh().findPatchID("wall");
volScalarField S11 = StressTensor.component(tensor::XX);

volVectorField gradS11 = fvc::grad(S11);
vectorField nearSurfaceGradS11 = gradS11.boundaryField()[wallPatchID].patchInternalField();
scalarField gradS11WallNormal = nearSurfaceGradS11 & surfaceNormal;

Compiles without errors. But I get an error message if I try to run the case.

#0 Foam::error::printStack(Foam:

stream&) in "/data/home/openfoam/OpenFOAM/OpenFOAM-1.5/lib/linux64GccDPOpt/libOpenFOAM.so"
#1 Foam::sigSegv::sigSegvHandler(int) in "/data/home/openfoam/OpenFOAM/OpenFOAM-1.5/lib/linux64GccDPOpt/libOpenFOAM.so"
#2 ?? in "/lib64/tls/libc.so.6"
#3 Foam::tmp<foam::field<foam::innerproduct<foam::vec tor<double>, Foam::Vector<double> >::type> > Foam::operator&<foam::vector<double>, Foam::Vector<double> >(Foam::
UList<foam::vector<double> > const&, Foam::UList<foam::vector<double> > const&) in "/data/home/openfoam/OpenFOAM/OpenFOAM-1.5/applications/bin/linux64GccDPOpt/lami nar
PTT"

It looks like having problems with the vector product in the last line?

Kerstin

spam3c · April 4, 2014, 06:05

Hi,

Do we have any option/tool in openfoam
like a post processing tool to compute pressure gradients in three directions in a 3D domain?

Thanks, regards

November 17, 2008, 08:11	Hi all, I tried this code a	#3
kerstin New Member Kerstin Heinen Join Date: Mar 2009 Location: Ludwigshafen, Germany Posts: 27 Rep Power: 17	Hi all, I tried this code above to calculate the gradient of a tensor component in normal direction to the wall... label wallPatchID = mesh.boundaryMesh().findPatchID("wall"); volScalarField S11 = StressTensor.component(tensor::XX); volVectorField gradS11 = fvc::grad(S11); vectorField nearSurfaceGradS11 = gradS11.boundaryField()[wallPatchID].patchInternalField(); scalarField gradS11WallNormal = nearSurfaceGradS11 & surfaceNormal; Compiles without errors. But I get an error message if I try to run the case. #0 Foam::error::printStack(Foam:stream&) in "/data/home/openfoam/OpenFOAM/OpenFOAM-1.5/lib/linux64GccDPOpt/libOpenFOAM.so" #1 Foam::sigSegv::sigSegvHandler(int) in "/data/home/openfoam/OpenFOAM/OpenFOAM-1.5/lib/linux64GccDPOpt/libOpenFOAM.so" #2 ?? in "/lib64/tls/libc.so.6" #3 Foam::tmp<foam::field<foam::innerproduct<foam::vec tor<double>, Foam::Vector<double> >::type> > Foam::operator&<foam::vector<double>, Foam::Vector<double> >(Foam:: UList<foam::vector<double> > const&, Foam::UList<foam::vector<double> > const&) in "/data/home/openfoam/OpenFOAM/OpenFOAM-1.5/applications/bin/linux64GccDPOpt/lami nar PTT" It looks like having problems with the vector product in the last line? Kerstin

April 4, 2014, 06:05	any quick post processing tool to compute pressure gradients in the domain	#4
spam3c New Member Sabrinho Gonzalez Join Date: Nov 2009 Posts: 5 Rep Power: 17	Hi, Do we have any option/tool in openfoam like a post processing tool to compute pressure gradients in three directions in a 3D domain? Thanks, regards Fahime likes this.

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January 14, 2008, 16:28	Hello, Can anyone tell me h	#1
qtian Member Quinn Tian Join Date: Mar 2009 Posts: 62 Rep Power: 17	Hello, Can anyone tell me how to the pressure gradient normal to the local wall surface? I have caculated pressure gradient at the first node away from surface. However, I don't know how to get the information of local normal vectors to the wall. Thanks

January 18, 2008, 06:29	p.boundaryField().snGrad();	#2
eugene Senior Member Eugene de Villiers Join Date: Mar 2009 Posts: 725 Rep Power: 21	p.boundaryField()[patchID].snGrad(); Which is generally zero for walls. You seem to want to extrapolate the pressure gradient. To do this you will need: volVectorField gradp = fvc::grad(p); vectorField nearSurfaceGradP = gradp.boundaryField()[patchID].patchInternalField(); const vectorField& surfaceNormal = mesh.boundary()[patchID].nf(); scalarField gradpWallNormal = nearSurfaceGradP & surfaceNormal;