Hi Mala, so a couple of things there - like others mentioned above your curved oval piece is made up of 2 faces, while surface to surface flow works only from one surface to another surface. You would probably want to rotate the circle used to generate the torus so as not to have the closed surface seam running right through the middle of where you want to do the flow.

The other thing is that it isn't really using the oval outline exactly, flow uses the rectangular "underlying surface". The oval trim boundary will be used just to shrink the rectangular underlying surface down so that it fits around the trim boundary.

So because of that you would generally want to make a rectangular plane as the base surface.

- Michael