In ANSYS CFX an error message appears indicating a too small inlet flow angle definiton for an Inlet boundary condition:
ERROR #002100024 has occurred in subroutine ASS_FLX_BDINIP.
The specified flow direction on boundaries must not be tangential
to the boundary. However, on the boundary patch Inflow
the specified flow direction is (nearly) tangential. Please do
one of the following:
(1) Check your direction specification on this boundary.
(2) Set the 'Flow Direction Linearisation' to 'Velocity Magnitude'
in your boundary specification.
This error is triggered when the angle between a face normal vector
and the specified direction vector is below a tolerance.
The default tolerance is 20 degrees, but may be modified by
setting the expert parameter 'tangential vector tolerance'.
From ANSYS CFX 11 to ANSYS CFX 12, the default threshold value for the inlet flow angle has been changed from 5 to 20 degrees measured against the circumferential direction.
Using the Expert Parameter `tangential vector tolerance = xx` (with "xx" being a value for the inflow angle, e.g. "10") enables the user to specify an own threshold in cases with smaller inflow angles than 20 degrees. Care should be taken with this setting, as too small values for the inflow angle can lead to unstable solver behavior.