Types Of Flow Lines In Fluid Mechanics - Pathlines, Streamlines, Streaklines, Timelines, Stream Tube
In order to visualize fluid flow, mainly three types of lines are defined. They are (i) streamline (ii) streak line, (iii) path line. They are same for steady flow but have importance in unsteady flow.
PathlinesPathline is a trajectory traced by the single fluid particle during its flow. It gives a traveling history of the fluid element over a specified time period. A path line can intersect itself at a different time.
StreamlinesIt is the curve used more often than the pathline. Streamline is an imaginary curve such that a tangent drawn on this curve represents the direction of instantaneous velocity at that point. Streamlines cannot intersect because a fluid particle cannot have two different velocities at the same time.
StreaklinesAnother form of visualization is a streakline. It is an instantaneous position of fluids that have passed through a fixed point of the flow field. To obtain streakline, a dye is injected into liquid or smoke in gas at a fixed point in the flow field so as to trace the subsequent position of fluid passing through it. So it is also called the dye line.
- In steady flow, there is no geometrical difference between pathline, streamline, and streakline (they are identical).
- There is no velocity component normal to the streamline.
TimelinesThe timeline is a set of the fluid particle that forms a line at a given instant.
Properties of stream tube
- Streamlines bound the stress tube.
- There is no flow across the imaginary walls of the stream tube. They can flow only through the ends.
- The flow through the stream tube is unidirectional.