- this provides internal consistency and allows direct use of the
  coordinate angle with sin(), cos() functions.
  It eliminates potential issues that could otherwise arise from
  alternative user input.

  Eg, in mixerFvMesh it would have previously been possible to specify
  the coordinate system to use degrees or radians, but these units were
  not checked when determining the tangential sweep positions.

NOTE: this may represent a breaking change if user coding has been
relying on cylindrical coordinate system in degrees.