# Boundary Conditions & Vector PDE solving

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 June 16, 2011, 23:03 Boundary Conditions & Vector PDE solving #1 New Member   Tanay Deshpande Join Date: Aug 2010 Posts: 20 Rep Power: 8 Hello Foamers, After learning the basics of OpenFOAM and its programming, I have two questions- 1. We need to specify the boundary condition of every defined field variable (p, U, temp, conc) at every patch in the 0/ directory. What happens if we do not know the BC beforehand? For example, if I'm writing a solver for laminar mixing of two species, one with conc=0 and the other with conc=1mol/m3 (at their respective inlets), what boundary conditions should I give for concentration at the walls and the outlet? zeroGradient doesn't help and fixedValue isn't possible. 2. For basic solvers (like laplacian, potential and scalarTransport PDEs), I've observed that the code is simply the euqtion statement solve(...==...); iterated a number of times with the controls being set by SIMPLE. But of course, for a vector equation like Navier-Stokes, the method is longer (predictor PEqn some n times- then corrector). So, if we have to code a scalar equation coupled to a vector e.g.- ddt(C) == laplacian(diff,C) - div(C,U) where U is the velocity vector will writing this equation statement in the outer loop of corr suffice to solve it? What if we wish to write another vector equation?

June 22, 2011, 10:22
#3
Senior Member

Santiago Marquez Damian
Join Date: Aug 2009
Location: Santa Fe, Santa Fe, Argentina
Posts: 430
Rep Power: 16
Tanay, I've attached a coupled solver for p-U-T, which was programmed following a tutorial (I think it is this one: http://www.tfd.chalmers.se/~hani/kur...ngTutorial.pdf). Excuse me for the Spanish comments, nevertheless you will be able to understand anyway. BC's you've posted are correct. So try and tells us how things have gone.

Regards.
Attached Files
 icoScalarTransportFoam.tar.gz (5.1 KB, 10 views)
__________________
Santiago MÁRQUEZ DAMIÁN, Ph.D.
Research Scientist
Research Center for Computational Methods (CIMEC) - CONICET/UNL
Tel: 54-342-4511594 Int. 7032
Colectora Ruta Nac. 168 / Paraje El Pozo
(3000) Santa Fe - Argentina.
http://www.cimec.org.ar

 June 23, 2011, 01:10 #4 New Member   Tanay Deshpande Join Date: Aug 2010 Posts: 20 Rep Power: 8 Santiago, He programado icoScalarTransport ya. Pero gracias por la ayuda. Yo no estaba funcionando correctamente Paraview en el caso de la concentración. Que acaba de añadir la ecuación de la temperatura para el circuito PISO exterior. Me pregunto si esto funciona incluso si queremos resolver algunos otros PDE con un volVectorField. Estoy trabajando en que en la actualidad.

 June 23, 2011, 07:16 #5 Senior Member     Santiago Marquez Damian Join Date: Aug 2009 Location: Santa Fe, Santa Fe, Argentina Posts: 430 Rep Power: 16 Tanay, I can't understand at all what are you referring to with coupling a volVectorField. Solving ddt(C) == laplacian(diff,C) - div(C,U) and U at the same time is exactly what icoScalarTransportFoam does. Regards. __________________ Santiago MÁRQUEZ DAMIÁN, Ph.D. Research Scientist Research Center for Computational Methods (CIMEC) - CONICET/UNL Tel: 54-342-4511594 Int. 7032 Colectora Ruta Nac. 168 / Paraje El Pozo (3000) Santa Fe - Argentina. http://www.cimec.org.ar

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