Class 3 Error

SYMPTOM:
When using the CEL variable 'taxis' in an expression, the resulting value is not what is expected.

PROBLEM:
Several points should be noted about the CEL variables "theta" and "taxis", and the post-processing variable "Theta".

1) The CEL variable "theta" is always atan2(y,x) in any coordinate frame. This means that it varies between -pi and +pi about the z axis and is zero at the x axis.

2) The post processing variable "Theta" (used in CFX Post), follows the convention for a "right handed" coordinate system, thus

- If the rotation axis is the z axis of a coordinate frame then "Theta" is evaluated as 'atan2(y,x)+pi'.
- If the rotation axis is the x axis of a coordinate frame then "Theta" is evaluated as 'atan2(z,y)+pi'.
- If the rotation axis is the y axis of a coordinate frame then "Theta" is evaluated as 'atan2(x,z)+pi'.

The range of "Theta" is therefore 0 to 2pi.

3) The CFX Solver always evaluates the CEL variable "taxis" using the Global Z axis in the absence of a rotation axis. This occurs even if a local Reference Coordinate Frame has been selected for use in a subdomain or boundary condition (Class 3 Error).

The range of "taxis" is currrently from -pi to +pi, when it should be 0 to 2pi.

4) CFX Post should allowusage of taxis/raxis in expressions, but it current


WORKAROUND:
The only workaround is to calculate the correct values of 'angle about an axis' using alternative expressions. This can be accomplished with a knowledge of the location of the desired axis.

FIXED IN:
Release 11.0.





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