Kinematics of Fluid Flow


Flow Types




Fluid Kinematics is the branch of fluid mechanics, which deals with time and space relationship such as velocity, acceleration, and discharge.

Path line:

            The path followed by a fluid particle is called path line.


            It is an imaginary line within the flow so that the tangent at any point and it indicates the direction of velocity at that point.

Streak line:

            It is curve, which gives an instantaneous picture of the location of the fluid particles, which had passed through a point.

Stream tube:

            It is fluid mass bounded by a group of streamlines.



Flow Types:

Laminar flow:

            In laminar flow the path lines, which are also streamlines, are parallel. Path lines are regular and do not cross one another. It occurs in viscous fluids or in fluid phenomena in which viscosity playas a predominate role.

Turbulent flow:

            Flow is said to be turbulent when its path lines are irregular curves crossing one another.

Steady flow:

            The flow is said to be steady when flow characteristics such as velocity, density, pressure, and temperature do not change with time. Mathematically dv/dt = 0.

Unsteady flow:

            The flow is said to be unsteady when the velocity and other characteristics changes with respect to time. Mathematically dv/dt 0. 

Uniform flow:

The flow is uniform when flow characteristics are constant in the reach

 Mathematically dv/ds=0 where s=distance measured from same fixed point on the path of flow. In other words, the flow characteristics are constant in the reach.

Ex: Uniform cross section.

Non-Uniform flow:

            The flow is non-uniform when flow characteristics changes at various points along the path. Mathematically dv/ds0. Ex: convergence or divergence.

Note: unless other wise mentioned, the flow will be assumed to be steady and uniform.

Incompressible flow:

            A fluid is said to be incompressible if it cannot be compressed easily. Almost all liquids are incompressible at ordinary temperature & pressure.

Compressible flow:

            Almost all gases behave like compressible fluids.

Note: unless other wise mentioned the liquid shall be assumed to be incompressible.




1. Fluid Mechanics, Hydraulics and Hydraulic Machines ľK.R.Arora.