I'll apologize ahead of time if there is an easier way to do this in CFD-Post. But the following method definitely works:
1. In Spaceclaim, create a centerline along the curved path in plan/sketch mode. In the 3D mode, pull the centerline equidistant on both side by a specified distance. Copy the newly created surface into to a new design and save it as a "stl" file.
2. (i) In CFD-Post, Location --> User Surface --> Method: From STL File and locate the file (make sure your units are correct!).
(ii) Now create a contour at the User Surface created and choose the appropriate dimensional variable (X or Y or Z, whichever direction you pulled your geometry in Spaceclaim).
(iii) Now Location --> Polyline --> Method: From Contour with the created contour name with the appropriate contour level.
This is just the method to create the centerline. You would have to write an equation to find the angle theta, so thay you can plot the centerline data with theta (degrees). You can play around with these options and plot all the graphs show above.
Another way is to create a session file with points along the centerline. You can use the session file to insert a certain number of plots along the elbow cenerline and plot it with the angles. This shouldn't be difficult too, but would require some trial and error.