GfsBcAngle is used to impose a contact angle on a given boundary for an interface defined by a GfsVariableTracerVOFHeight.
The syntax in parameter files is
[ GfsBc ] [ GfsFunction ]
where the GfsFunction returns the value of the contact angle in degrees. Note that the contact angle is defined for the phase for which the VOF tracer volume fraction is one (i.e. the contact angle for the other phase is 180 - GfsFunction).