[cfdnewb123]

I can't find anywhere on Fluent which uses streamline coordinate. For instance, I need the flow velocity along the streamline and the derivative of the velocity w.r.t. the normal of its streamline.

Fluent's x[ND_ND] seems to be for x-y Cartesian coordinate and likewise is its velocity gradient (C_DUDX). Is there anyway I can convert to streamline coordinate?

[vinerm]

The only coordinate available in Fluent is spatial and that's too in Cartesian. One solution is to write the pathlines. Those are nothing but particles tracks for massless particles. These will have all the information you need, i.e., velocities at each point on the path, representing streamlines and then you can determine gradient using difference in velocities along the normal, which essentially requires calculation of curvature.