How to obtain a wall normal vector that can be used in a solver CEL expression?

In the CFX solver the wall normal variables Normal X etc. are not available for CEL expressions. However, this vector is required if you are interested i.e. in computing a wall tangential velocity i.e. on a moving bent belt.

Steps to obtain the wall normal vector for CEL:
1. run a simulation without the wall velocity specified for 1 time step
2. open the result file in CFD-Post
3. export the Normal X, Normal Y, Normal Z variables into a csv file
4. modify the csv-file to a profile file format
5. open CFX-Pre and load the csv-file as profile data
6. Now the variables are available as functions and can be used in CEL expressions.

For the example of a moving belt, a wall tangential vector can be calculated from the wall normal vector. Normalizing is and multiplying with the constant belt velocity provides a wall tangential velocity that is always tangential to the wall and has the correct magnitude.

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