- in most cases already checked valid() so don't need additional check
  for setting an existing pointer

When the GeometricBoundaryField template class was originally written it
was a separate class in the Foam namespace rather than a sub-class of
GeometricField as it is now.  Without loss of clarity and simplifying
code which access the boundary field of GeometricFields it is better
that GeometricBoundaryField be renamed Boundary for consistency with the
new naming convention for the type of the dimensioned internal field:
Internal, see commit a25a449c

This is a very simple text substitution change which can be applied to
any code which compiles with the OpenFOAM-dev libraries.

Resolves bug-report http://www.openfoam.org/mantisbt/view.php?id=1938

Because C++ does not support overloading based on the return-type there
is a problem defining both const and non-const member functions which
are resolved based on the const-ness of the object for which they are
called rather than the intent of the programmer declared via the
const-ness of the returned type.  The issue for the "boundaryField()"
member function is that the non-const version increments the
event-counter and checks the state of the stored old-time fields in case
the returned value is altered whereas the const version has no
side-effects and simply returns the reference.  If the the non-const
function is called within the patch-loop the event-counter may overflow.
To resolve this it in necessary to avoid calling the non-const form of
"boundaryField()" if the results is not altered and cache the reference
outside the patch-loop when mutation of the patch fields is needed.

The most straight forward way of resolving this problem is to name the
const and non-const forms of the member functions differently e.g. the
non-const form could be named:

    mutableBoundaryField()
    mutBoundaryField()
    nonConstBoundaryField()
    boundaryFieldRef()

Given that in C++ a reference is non-const unless specified as const:
"T&" vs "const T&" the logical convention would be

    boundaryFieldRef()
    boundaryFieldConstRef()

and given that the const form which is more commonly used is it could
simply be named "boundaryField()" then the logical convention is

    GeometricBoundaryField& boundaryFieldRef();

    inline const GeometricBoundaryField& boundaryField() const;

This is also consistent with the new "tmp" class for which non-const
access to the stored object is obtained using the ".ref()" member function.

This new convention for non-const access to the components of
GeometricField will be applied to "dimensionedInternalField()" and "internalField()" in the
future, i.e. "dimensionedInternalFieldRef()" and "internalFieldRef()".

The deprecated non-const tmp functionality is now on the compiler switch
NON_CONST_TMP which can be enabled by adding -DNON_CONST_TMP to EXE_INC
in the Make/options file.  However, it is recommended to upgrade all
code to the new safer tmp by using the '.ref()' member function rather
than the non-const '()' dereference operator when non-const access to
the temporary object is required.

Please report any problems on Mantis.

Henry G. Weller
CFD Direct.

This formulation provides C-grid like pressure-flux staggering on an
unstructured mesh which is hugely beneficial for Euler-Euler multiphase
equations as it allows for all forces to be treated in a consistent
manner on the cell-faces which provides better balance, stability and
accuracy.  However, to achieve face-force consistency the momentum
transport terms must be interpolated to the faces reducing accuracy of
this part of the system but this is offset by the increase in accuracy
of the force-balance.

Currently it is not clear if this face-based momentum equation
formulation is preferable for all Euler-Euler simulations so I have
included it on a switch to allow evaluation and comparison with the
previous cell-based formulation.  To try the new algorithm simply switch
it on, e.g.:

PIMPLE
{
    nOuterCorrectors 3;
    nCorrectors      1;
    nNonOrthogonalCorrectors 0;
    faceMomentum     yes;
}

It is proving particularly good for bubbly flows, eliminating the
staggering patterns often seen in the air velocity field with the
previous algorithm, removing other spurious numerical artifacts in the
velocity fields and improving stability and allowing larger time-steps
For particle-gas flows the advantage is noticeable but not nearly as
pronounced as in the bubbly flow cases.

Please test the new algorithm on your cases and provide feedback.

Henry G. Weller
CFD Direct

Updated tutorials to converge pressure during PIMPLE loop to avoid
phase-fraction unboundedness which limits thermodynamics convergence.

Reduces or eliminates staggering patterns due to cell-force imbalances
Resolves bug-report http://www.openfoam.org/mantisbt/view.php?id=1363