Kinematics and Dynamics of Flow Fluid Mechanics Tutorials
👉Define the terms streamlines and pathlines.
Streamlines: 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. Since a fluid is composed of fluid particles, the pattern of flow of fluid may be represented by a series of streamlines, obtained by drawing a series of curves through the flowing fluid such that the velocity vector at any point is tangential to the curves.
Pathlines: A path line is the line traced by a single fluid particle as it moves over a period of time. Thus a path line indicates the direction of Velocity of the same fluid particle at successive instants of time. While a streamline shows the direction of velocity of a number of fluid particles at the same instant of time.
A fluid particle always moves tangent to the streamline thus. for steady flow, the path lines and streamlines are identical.
The instantaneous pictures of the position of all fluid particles, which have passed through a given point at some previous time are called streak lines or filament lines.
In experimental work, often a colour or dye or some other substance (such as smoke in case of gases) is injected intothe flOWing fluid, in order to trace the motion of the fluid particles. The resulting trail of colour is known as streak line.
In steady flow, since there is no change in the flow pattern, a streak line is same as a streamline and the path line of a particle. in unsteady flow a streak line at an instant is the locus of end points of particle paths (or path lines) that started at the instant the particle passed through the injection point. For a steady flow, all above mentioned three lines, viz. Streamline, Pathline and Streakline are indentical.