In order to visualize fluid flow, mainly three types of flow lines are defined.
They are :
(i) Streamline
(ii) Streak line
(iii) Path line
(i) Streamline :
•A streamline is an imaginary line drawn through a flowing fluid in such a way that the tangent to it at any point gives the direction of the velocity of flow at that point.
• Streamlines are useful as they are indicators of the instantaneous direction of fluid motion throughout a flow field.
*Streamtube :
• A stream tube is a tube imagined to be formed by a group of streamlines passing through a small closed curve, which may or may not be circular.
(ii) Streak Line :
• A streakline is the path that a particle will follow in the flow, the locus of particles that have passed sequentially through a prescribed path in the flow.
'or'
A streak line is the locus of the temporary locations of all particles that have passed though a fixed point at any instant of time.
(iii) Path Line :
•A path line is the path traced by a single fluid particle at different instants of time.
Thus, a path line indicates the direction of velocity of the same fluid particle at successive instants of time
• For a steady flow,
all the three lines, viz. streamline, path line and streak line are identical.
* Timeline :
