Using the same tool as shown in the previous video
This shows how rheotomic surfaces are made from the imaginary part of a complex function. Contours of this surface are streamlines of a potential flow.
If we take the real part of the same complex function, we get a surface whose contours are the corresponding orthogonal equipotentials.
The 2 parts can be combined to give a surface with spiralling contours, and if a linear flow is added, it makes the entire surface slope in a particular direction.
More details and download here: