FAQ/Physical

1 FAQ Section 3: Physical

Questions about the physics implemented (boundary conditions and similar)

1.1 General

1.1.1 What is the meaning of the Field X

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

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

You don't. Instead of the dynamic viscosity $\mu$ the kinematic viscosity $\nu=\frac{\mu}{\rho}$ 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.

1.1.3 What is the field phi that the solver is writing?

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

For more information, see also this table.

1.2 Boundary Conditions

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

The zeroGradient boundary condition sets the boundary value to the near-wall cell value.

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

(Source: [1])

1.2.2 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: [2])

1.3 Turbulence modeling

1.3.1 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: [3])

1.4 Additional models

Has OpenFOAM been used to calculate this type of problems?

1.4.1 Eulerian two fluid model and granular flow

They are implemented in twoPhaseEulerFoam.

1.4.2 Viscoelastic flows?

Have been done. Will be released. For details see this thread on the Message Board.