In most boundary conditions, fvOptions etc. required and optional fields
to be looked-up from the objectRegistry are selected by setting the
keyword corresponding to the standard field name in the BC etc. to the
appropriate name in the objectRegistry.  Usually a default is provided
with sets the field name to the keyword name, e.g. in the
totalPressureFvPatchScalarField the velocity is selected by setting the
keyword 'U' to the appropriate name which defaults to 'U':

        Property     | Description             | Required    | Default value
        U            | velocity field name     | no          | U
        phi          | flux field name         | no          | phi
        .
        .
        .

However, in some BCs and functionObjects and many fvOptions another
convention is used in which the field name keyword is appended by 'Name'
e.g.

        Property     | Description             | Required    | Default value
        pName        | pressure field name     | no          | p
        UName        | velocity field name     | no          | U

This difference in convention is unnecessary and confusing, hinders code
and dictionary reuse and complicates code maintenance.  In this commit
the appended 'Name' is removed from the field selection keywords
standardizing OpenFOAM on the first convention above.

Contributed by Bruno Santos
Resolves patch report http://www.openfoam.org/mantisbt/view.php?id=2023

Update online documentation http://openfoam.github.io/Documentation-dev/html/

The boundary conditions of HbyA are now constrained by the new "constrainHbyA"
function which applies the velocity boundary values for patches for which the
velocity cannot be modified by assignment and pressure extrapolation is
not specified via the new
"fixedFluxExtrapolatedPressureFvPatchScalarField".

The new function "constrainPressure" sets the pressure gradient
appropriately for "fixedFluxPressureFvPatchScalarField" and
"fixedFluxExtrapolatedPressureFvPatchScalarField" boundary conditions to
ensure the evaluated flux corresponds to the known velocity values at
the boundary.

The "fixedFluxPressureFvPatchScalarField" boundary condition operates
exactly as before, ensuring the correct flux at fixed-flux boundaries by
compensating for the body forces (gravity in particular) with the
pressure gradient.

The new "fixedFluxExtrapolatedPressureFvPatchScalarField" boundary
condition may be used for cases with or without body-forces to set the
pressure gradient to compensate not only for the body-force but also the
extrapolated "HbyA" which provides a second-order boundary condition for
pressure.  This is useful for a range a problems including impinging
flow, extrapolated inlet conditions with body-forces or for highly
viscous flows, pressure-induced separation etc.  To test this boundary
condition at walls in the motorBike tutorial case set

    lowerWall
    {
        type            fixedFluxExtrapolatedPressure;
    }

    motorBikeGroup
    {
        type            fixedFluxExtrapolatedPressure;
    }

Currently the new extrapolated pressure boundary condition is supported
for all incompressible and sub-sonic compressible solvers except those
providing implicit and tensorial porosity support.  The approach will be
extended to cover these solvers and options in the future.

Note: the extrapolated pressure boundary condition is experimental and
requires further testing to assess the range of applicability,
stability, accuracy etc.

Henry G. Weller
CFD Direct Ltd.

It is better to declare the namespace of each function in the C file
rather than "open" the namespace as this may lead to inconsistencies
between the declaration in the H files and definition in the C file.

Avoids the clutter and maintenance effort associated with providing the
function signature string.

Needed to create generic compressible turbulence model library