EngArc - L - Streamlines, Streaklines, Pathlines, Timelines

Streamlines, Streaklines, Pathlines, Timelines

Quick
A streamline is a line that is everywhere tangent to the instantaneous local velocity vector. A streamline represents a velocity path.
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.
A pathline is the path that is followed by a particle released into the fluid; the actual path traversed by a given fluid particle. A pathline represents a particle's path.
A timeline is lines that represent the same set of fluid particles but which show their position at different moments in time.

Details

Streamlines	a line that is everywhere tangent to the instantaneous local velocity vector.
Streaklines	particles are continuously introduced at a certain point, the streakline shows the line formed due to the release of these particles from the specific point. It is the locus of particles that have passed sequentially through a prescribed path in the flow. Just below this table further describes the difference between streaklines and pathlines.
Pathlines	represents the path that is followed by one particle released into the fluid; the actual path traversed by a given fluid particle. Pathlines may be referred to as flow lines in physics. Just below this table further describes the difference between streaklines and pathlines.
Timelines	lines that represent an array of fluid particles and show the position of the array at different moments in time. If one point was taken on a timeline and traced with time, a pathline would be obtained.

The images above look identical for streaklines and pathlines, but for turbulent and transitional flow, they may differ. The path one particle travels may be a different path for another particle that is released at the same point, but at a later time. See the following:


Pathline for a particle released at an initial point in time.	Pathline shows path for the second particle, released from the same point but at a later time, the pathline is different because the flow has changed.

Streamlines

Streamlines are useful as indicators of the instantaneous direction of fluid motion throughout a flow field. Regions of recirculating flow and separation of a fluid off of a solid wall are easily identified with streamlines.