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January 26, 2013, 05:28 
Zeroth order interpolation

#21 
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Lorenzo A. Ricciardi
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Hi all,
Is there a way to force a "flat" (i.e. zeroth order) cell to face interpolation using the above mentioned interpolate method? Thanks 

January 31, 2013, 03:30 

#22 
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Mahdi Hosseinali
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What do you mean by flat cell? that would be against FVM definition of spatial discretization.


January 31, 2013, 08:56 

#23 
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Lorenzo A. Ricciardi
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"Flat" was relative to the interpolation, not to the cell. Call it constant interpolation (or zeroth order), if you prefer.
I don't agree with you about flat interpolation being against FVM. When you pass from a generic nonlinear hyperbolic equation like d/dt (u) + div(F(u)) = 0 // d is partial time derivative to a semi discrete form, you have to integrate on the cell volume. The div term becomes a surface integral, but (if the cell geometry is constant) the partial time derivative becomes the time derivative of a volume integral. The equation is divided by the volume of the cell, and you have an ODE for each cell averaged value. Thus each value is "flat" inside the cell. I'm implementing a particular solver in openFoam, which uses Riemann solvers, and although I will definitely use some kind of limited interpolation of values to the surface to get high resolution, for testing and completeness considerations I'm trying to use the unified "interpolate" function to assign a value from a volumeField to a surfaceField. I solved the problem with a very simple routine I've written from scratch, but it doesn't work in parallel so far: Code:
for (label faceI = 0; faceI < mesh.nInternalFaces(); faceI++) { label cellI = mesh.faceOwner()[faceI]; rho_neg[faceI] = rho[cellI]; U_neg[faceI] = U[cellI]; lambda_neg[faceI] = lambda[cellI]; label cellJ = mesh.faceNeighbour()[faceI]; rho_pos[faceI] = rho[cellJ]; U_pos[faceI] = U[cellJ]; lambda_pos[faceI] = lambda[cellJ]; } Thanks 

January 31, 2013, 12:23 

#24 
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Mahdi Hosseinali
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I know how FVM works, what you want is piece wise constant while usually piece wise linear is being used. I believe you are going to use Gudonove type methods which still would yield a better result if you use piecewise linear rather than constant.
Anyway, there is a simple way to interpolate from vol<type>Field to surface<Type>Field, and that is fvc::interpolate, look it up in Doxygen. Also you might wanna take a look at the solver rhoCentralFoam, it is using what you are after. 

January 31, 2013, 15:11 

#25 
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Lorenzo A. Ricciardi
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I know Godunov method, and that's why I'm implementing another solver, different even from RhoCentralFoam
I'll try to look deeper inside Doxygen, thanks anyway 

June 30, 2013, 07:48 

#26  
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Bruno Santos
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Greetings to all!
In reference to the following quotes, I believe that the missing link is this thread: Some results with a new compressible flow solver The OpenFOAM Forum changed software a few times, so it's normal that some links are still broken Quote:
Quote:
Quote:
Bruno 

August 26, 2013, 11:15 

#27 
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Ehsan
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can anyone explain the lines or steps of rhoCentralFoam solver?
or a link or any instruction?
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December 24, 2013, 17:02 

#28 
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Ehsan
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Hi all,
there is a link about densitybased solvers in Fluent site:http://aerojet.engr.ucdavis.edu/flue...htm#ramscheme that says all densitybased solvers are coupled. does rhoCentralFoam solve equations in a segregated way or coupled way?
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December 28, 2013, 17:20 

#29  
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Bruno Santos
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Hi Ehsan,
Quote:
Quote:
Nonetheless, if you already have an overview of the equations being solved in rhoCentralFoam, it should be somewhat clear if it's segregated or coupled, from the way that the equations are solved: http://www.cfdonline.com/Wiki/Fluen...ated_solver.3F Best regards, Bruno
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April 15, 2014, 04:05 

#30 
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anshul bansal
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Hi...
can u please explain what means by these terms... rhoU ,rPsi, e, phiv, tauMC, sigmaDotU and phiEp... Thanks Anshul 

April 16, 2014, 04:18 

#31  
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Ehsan
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Quote:
rhoU=rho*U rPsi=R*T phiv=A*U (I have some doubt about it) phiEp=rho*A*U and two other terms are related to turbulence models and viscosity. definition of terms there are in solver codes.
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April 16, 2014, 05:19 

#32 
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anshul bansal
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hi..
thanks... here A= area or some other mean...?? and is there any description file where i can get these definition ?? Anshul 

April 16, 2014, 06:50 

#33 
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anshul bansal
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ohh... i get this..
here A=rho*U means mass flow is is right.?? 

April 16, 2014, 10:06 

#34 
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Ehsan
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A is the normal area of the cell to outside (inflow or outflow). unfortunately there is not a complete guide. phi in open foam is the mass flux and phiv is volumetric mass flux as I remember and is about incompressible problems.
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April 18, 2014, 15:04 

#35 
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anshul bansal
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hi immortality,
in rhoCentralFoam.c what mean by mesh.Sf() (in 105 line, openfoam 2.2.1 version) i attach this file thanks anshul 

April 18, 2014, 15:33 

#36  
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Ehsan
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Quote:
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April 22, 2014, 14:20 

#37 
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anshul bansal
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hi immortality,
thanks for reply. i have another last doubt... which can help me very much. can u explain this sigmaDotU.... what this muEff and snGrad(U) ?? and this equation //  Solve energy surfaceScalarField sigmaDotU ( ( fvc::interpolate(muEff)*mesh.magSf()*fvc::snGrad(U ) + (mesh.Sf() & fvc::interpolate(tauMC)) ) & (a_pos*U_pos + a_neg*U_neg) ); 

August 20, 2014, 02:46 
A little question: rhoCentralFoam implementation

#38 
Member

Hi,
I'm trying to understand the implementation of rhoCentralFoam. I check the original paper of Greenshield, but I found some discrepancies between theory and implementation. in the attached document I explain my doubts. If anyone can help me, I'll be very thankful. Thanks in advance https://copy.com/1mcVjlWREUPt Felipe by the way if anyone want to try copy (better than dropbox!!) https://copy.com?r=HYM0VM
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August 6, 2015, 10:58 

#39 
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Wen Xu
Join Date: May 2014
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Dear Luca and Alberto,
a = Grad(x) = (PHI (i, j)  PHI(i1, j))/ deltaX I have several questions about the upwind scheme:
Please help me..... Thank you very much!!! Best regards, Wen 

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