Lagrangian description of fluid field is more computational because It required to track the movement of a large number of fluid particles with time.

The study of the motion of the fluid without any reference of force is known as fluid kinematics.

There are two descriptions to define fluid motion.

• Lagrangian Description.
• Eulerian Description.

Lagrangian Description:

• The Lagrangian description is one in which individual fluid particles are tracked, much like the tracking of billiard balls in a high school physics experiment.
• In the Lagrangian description of fluid flow, individual fluid particles are "marked," and their positions, velocities, etc. are described as a function of time.
• The physical laws, such as Newton's laws and conservation of mass and energy, apply directly to each particle.
• If there were only a few particles to consider, as in a high school physics experiment with billiard balls, the Lagrangian description would be desirable.
• Lagrangian approach deals with the Identification of a fluid particle; tracking (or follow) it as it moves, and monitoring change in its properties.
• The properties may be velocity, temperature, density, mass, or concentration, etc. in the flow field.
• However, fluid flow is a continuum phenomenon, at least down to the molecular level. It is not possible to track each "particle" in a complex flow field.
• Thus, the Lagrangian description is rarely used in fluid mechanics.