411 REFERENCE · Wikibooks
Jet Propulsion/Streamline
Reference material by Wikibooks contributors. This retains its source identity and is not 411 news reporting.
In fluid dynamics, a streamline is a line which is everywhere tangent to the velocity of the flow.
This implies that if u is the velocity vector at a point and dr is the vector in the direction of the streamline, then their cross product is zero.
u x dr = 0.
This translates to,
where u = ui + vj+ wk
and dr = dxi + dyj + dzk.