How to find the curvature of streamlines
 

Dear Foamers,
In my simulations, I need to add curvature-induced flux which requires the information about the unit normal vector in the radially outward direction in curved streamline shear flows and the curvature of the streamlines.

Can anybody please help me how to calculate the unit normal vector in the radially outward direction in curved streamline shear flows and the curvature of the streamlines?

I would greatly appreciate any suggestions and be attentive.

Shadab