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Creating a solver for the nondimensionalized NavierStokes equation 

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November 15, 2012, 11:52 
Creating a solver for the nondimensionalized NavierStokes equation

#1 
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Mehrez
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Hi everyone,
I have recently started using OpenFoam. I want to resolve the nondimensionalized NavierStakes equation (in which appears the Reynolds number). My equation is ( you can also find it attached ) : Re . (U . div) U + grad(meanP)  laplacian(U) =  grad(fluctP) meanP is a unit vector which is constant and P=meanP+fluctP Re is the reynolds number I want to resolve my equation for U and fluctP For this, I have modified the IcoFoam solver as follows, but it seems that there is an error ( may be with the '' meanP '' ) fvVectorMatrix UEqn ( fvm::ddt(U) + Re*(fvm::div(phi, U))  fvm::laplacian(U) + magSqr(meanP) ); solve(UEqn == fvc::grad(fluctP)); I will be thankfull If someone can help me to create this solver or share a web site which treated the implementation of the nondimensionalized NS equation. Best regards Mehrez Last edited by Mehrez; November 16, 2012 at 06:04. 

November 16, 2012, 05:01 

#2 
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Mehrez
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Hi
Can someone help me please. Thank you 

November 16, 2012, 05:49 

#3 
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Mehrez
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please find attached the OpenFoam files of the solver (I have proceeded by modifying the IcoFoam solver to myIcoFoamB solver).


November 16, 2012, 06:39 

#4 
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Tobias Holzmann
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Hi,
there are many errors: Code:
fvVectorMatrix UEqn ( fvm::ddt(U) + Re*(fvm::div(phi, U))  fvm::laplacian(U) + magSqr(meanP) ); Code:
laplacian(nu, U) OF do not know what meanP is. So you have to define Re meanP and the other variables you implemented! The following example is working: Code:
fvVectorMatrix UEqn ( fvm::ddt(U) + fvm::div(phi, U)  fvm::laplacian(nu, U)  fvc::grad(p) ); solve(UEqn == fvc::grad(p)); 

November 16, 2012, 06:50 

#5 
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Hisham Elsafti
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Hi Mehrez,
First it would be better if you modify the Make/files as in the user guide chapter 3 to be: Code:
myIcoFoamB.C EXE = $(FOAM_USER_APPBIN)/myIcoFoamB Code:
createFields.H: In function ‘int main(int, char**)’: createFields.H:23:5: error: no matching function for call to ‘Foam::GeometricField<Foam::Vector<double>, Foam::fvPatchField\ , Foam::volMesh>::GeometricField(Foam::ITstream&)’ createFields.H:23:5: note: candidates are: Code:
volVectorField gradP ( transportProperties.lookup("gradP") ); Code:
volVectorField gradP ( IOobject ( "gradP", runTime.timeName(), mesh, IOobject::NO_READ, IOobject::NO_WRITE ), fvc::grad(p) ); Code:
myIcoFoamB.C:61:18: error: no match for ‘operator+’ in ‘Foam::operator(const Foam::tmp<Foam::fvMatrix<Type> >&, const Foam\ ::tmp<Foam::fvMatrix<Type> >&) [with Type = Foam::Vector<double>]((*(const Foam::tmp<Foam::fvMatrix<Foam::Vector<double> > \ >*)(& Foam::fvm::laplacian(const Foam::GeometricField<Type, Foam::fvPatchField, Foam::volMesh>&) [with Type = Foam::Vector<\ double>]()))) + Foam::magSqr(const Foam::GeometricField<Type, PatchField, GeoMesh>&) [with Type = Foam::Vector<double>, Pat\ chField = Foam::fvPatchField, GeoMesh = Foam::volMesh]()’ myIcoFoamB.C:61:18: note: candidates are: Code:
fvVectorMatrix UEqn ( fvm::ddt(U) + Re*(fvm::div(phi, U))  fvm::laplacian(U) + magSqr(gradP) ); Best regards, Hisham 

November 16, 2012, 07:34 

#6  
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Tobias Holzmann
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Quote:
I just had a very short look into the code and dont see the declaration of the other variables Well nice replay! Code:
( fvm::ddt(U) + Re*(fvm::div(phi, U))  fvm::laplacian(nu, U) + magSqr(gradP) ); 

November 16, 2012, 07:43 

#7 
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Mehrez
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Hi guys
Thank you for your help. I think that it is better if you take a look to my equation (which I have attached in my first message). You can see that I don't have : nu . laplacian (U) but I just have : laplacian (U) Concerning the declaration of the variables : I have declared " Re " and " gradP " in the file createFields.H dimensionedScalar Re ( transportProperties.lookup("Re") ); volVectorField gradP ( transportProperties.lookup("gradP") ); 

November 16, 2012, 07:58 

#9 
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Mehrez
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Hi Hisham
Thank you for your answer. I think that I don't have to declare " gradP " like this : volVectorField gradP ( IOobject ( "gradP", runTime.timeName(), mesh, IOobject::NO_READ, IOobject::NO_WRITE ), fvc::grad(p) ); As I said before, the '' gradP '' is a unit vector which is constant and which I put it like an input (so this is why OF don't have to compute it). I have just to declare it like a vector which I will specify the value in constantProperties file. 

November 16, 2012, 08:01 

#10  
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Tobias Holzmann
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Quote:
But how whould you get the information of the "vector" couse the pressure is just a scalar without a direction. 

November 16, 2012, 08:06 

#11 
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Mehrez
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Hi Tobi
As you can see in my equation gradP is the gradient of the nondimensionalized mean pressure. I have it like an input (I will study my flow in function of given values of Re and gradP) I think that the problem is how to define this vector (gradP) in the equation 

November 16, 2012, 08:15 

#12 
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Mehrez
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I think that it is more clear like this
Equation : Re . (U . div) U + gradP  laplacian(U) =  grad(fluctP) OF syntax : fvVectorMatrix UEqn ( fvm::ddt(U) + Re*(fvm::div(phi, U))  fvm::laplacian(U) + magSqr(gradP) ); solve(UEqn == fvc::grad(fluctP)); Input : Re : scalar gradP : vector output (after computation) U : vector field fluctP : vector field 

November 16, 2012, 11:22 

#13 
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Bernhard
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If gradP is a constant vector, you should not store it in a volVectorField, but in a dimensionedVector from the transportproperties.
Two more things:  Are you sure Reynolds should appear like you wrote it. As far as I know, in the dimensionless NS equations, you have 1/Re in the diffusive terms.  You're now adding magSqr(gradP), which is a scalar, to a vector equation. This can not be correct. 

November 16, 2012, 11:52 

#14 
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Mehrez
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Dear Bernhard,
I'm sure that I have a right equation (attached here) Thank you very much for your help. Actually I can compile my solver with your corrections. fvVectorMatrix UEqn ( fvm::ddt(U) Re*(fvm::div(phi, U))  fvm::laplacian(U) + gradP ); and : dimensionedVector gradP ( transportProperties.lookup("gradP") ); To test this solver, I've taken the attached example "cavity" after putting U, p, Re, and gradP in a dimensionless form. I've done the same with the domain (I've commented the line " conversion to meters " ). Executing "cavity" with "myIcoFoamB" solver, OpenFoam returns an error message on the dimensions: > FOAM FATAL ERROR: incompatible dimensions for operation [U [0 1 0 0 0 0 0]]  [U [0 2 0 0 0 0 0]] I think it comes from the operators (grad gives : L ^ 1 and Laplacian gives : L ^ 2). Is there a way to put the components (x, y, z) of the domain in a dimensionless form in order to get dimensionless values by applying one of the operators? Thank you very much for your help. Best regards. Mehrez 

November 16, 2012, 12:24 

#15 
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Bernhard
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Complicated one, you can choose to ignore the dimensionchecking. I think you can do this in the controlDict you find in ..../OpenFOAM2.1.x/etc/ .
Maybe you can put it in your own controlDict as well. I never tested this, but you can look here. 

November 16, 2012, 12:43 

#17 
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Mehrez
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Hi guys,
Again thanks for your precious help. @ Bernhard : I have found the file " controlDict " , can you please precise me how to proceed. @ Tobi : I've tried what you said but it doesn't work. it returns each time a different dimensions error ! I can't understand Mehrez 

November 16, 2012, 12:56 

#19 
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Mehrez
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Re Re [ 0 0 0 0 0 0 0 ] 0.01;
gradP gradP [ 0 0 0 0 0 0 0 ] (0.9 0.2 0); U : dimensions [0 0 0 0 0 0 0]; p : dimensions [0 0 0 0 0 0 0]; In the blockMeshDict, I have commented the following line : //convertToMeters 0.1; and this is what I get : Create time Create mesh for time = 0 Reading transportProperties Reading field p Reading field U Reading/calculating face flux field phi Starting time loop Time = 0.005 Courant Number mean: 0 max: 0 > FOAM FATAL ERROR: incompatible dimensions for operation [U[0 1 0 0 0 0 0] ]  [U[0 2 0 0 0 0 0] ] From function checkMethod(const fvMatrix<Type>&, const fvMatrix<Type>&) in file /opt/openfoam211/src/finiteVolume/lnInclude/fvMatrix.C at line 1316. FOAM aborting #0 Foam::error:rintStack(Foam::Ostream&) in "/opt/openfoam211/platforms/linuxGccDPOpt/lib/libOpenFOAM.so" #1 Foam::error::abort() in "/opt/openfoam211/platforms/linuxGccDPOpt/lib/libOpenFOAM.so" #2 in "/opt/openfoam211/platforms/linuxGccDPOpt/bin/myIcoFoamB" #3 in "/opt/openfoam211/platforms/linuxGccDPOpt/bin/myIcoFoamB" #4 in "/opt/openfoam211/platforms/linuxGccDPOpt/bin/myIcoFoamB" #5 __libc_start_main in "/lib/i386linuxgnu/libc.so.6" #6 in "/opt/openfoam211/platforms/linuxGccDPOpt/bin/myIcoFoamB" Aborted (core dumped) ubuntu@ubuntuVirtualBox:~/OpenFOAM/mehrez2.1.1/test/cavity$ 

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navierstokes solver, openfoam 
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