View source for FAQ/Physical

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[[Category:FAQSection]]

== FAQ Section [[faqnumber::3]]: [[faqname::Physical]] ==
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[[faqdescription::Questions about the physics implemented (boundary conditions and similar)]]
=== General ===

==== What is the meaning of the Field X ====

A table of the fields most commonly written by OpenFOAM-solvers can be found [[Uguide_table_of_fields|here]].

==== Where do I enter the fluid-density for [[icoFoam]], [[turbFoam]] and other incompressible solvers? ====

You don't. Instead of the dynamic viscosity <math>\mu</math> the kinematic viscosity <math>\nu=\frac{\mu}{\rho}</math> is used by the  OpenFOAM-solvers.

Note: the pressure has to be normalized with the density, too.  One consequence of this is that the dimensions of pressure become pressure divided by density.

==== What is the field <tt>phi</tt> that the solver is writing? ====

The mass flow through the cell faces (<math>\rho \vec u \cdot \vec A</math> with <math>\vec A</math> the area of the face). Keep in mind that solvers for incompressible flow will unlikely use <math>\rho</math>.

For more information, see also [[Uguide_table_of_fields|this table]].

=== Boundary Conditions ===

==== What's the difference between the symmetryPlane and the zeroGradient boundary conditions? ====

The <tt>zeroGradient</tt> boundary condition sets the boundary value to the near-wall cell value. 

A <tt>symmetryPlane</tt> boundary condition is a symmetry-plane which is equivalent to a <tt>zeroGradient</tt> for scalars, but not for vectors or tensors.

(Source: [http://openfoam.cfd-online.com/forum/messages/1/625.html])

==== What does the lInf parameter mean in pressureTransmissive boundary condition? ====

lInf is the relaxation length-scale (in m) for outgoing pressure waves to return to pInf. This stops the pressure in the domain from floating about if the inlet pressure is not specified. (source: [http://openfoam.cfd-online.com/forum/messages/1/630.html])

=== Turbulence modeling ===

==== How is wall-functions for RANS disabled and enabled? ====

All high-Re RANS turbulence models include wall-functions because it is inappropriate to use them without. Only the low-Re models operate without wall-functions as they include model-specific wall treatments.

(Source: [http://openfoam.cfd-online.com/forum/messages/1/541.html])

=== Additional models ===

Has OpenFOAM been used to calculate this type of problems?

==== Eulerian two fluid model and granular flow ====

They are implemented in twoPhaseEulerFoam.

==== Viscoelastic flows? ====

Have been done. Will be released. For details see [http://openfoam.cfd-online.com/forum/messages/1/183.html this thread on the Message Board].
Faqdescription	Questions about the physics implemented (boundary conditions and similar) +
Faqname	Physical +
Faqnumber	3 +