Sorry for the confusion everyone, when I initially posted I used the term "parabola" to generally describe the shape, but as far as I know there really isnt a "true" classic shape that the fuel flows in, mainly because of the non-homogenous pressure in the exhaust plume:   As you can see here, it actually starts as mostly straight out, then quickly curves outwards before beginning to curve back inwards.  I say "parabola" because its a fairly common shape that people know, but real