Fluids in motion

Fluids in motion:

The branch of physics which deals with the study of properties of fluids in motion is called hydrodynamics. As the study of motion of real fluid is very complicated, we shall limit our study to the motion of an ideal fluid. 

The figure above shows a pipe whose direction and cross sectional area change arbitrarily. The direction of flow of ideal fluid in pipe is as shown. We define a few terms used to describe flow of a fluid.

Steady flow: 

Measurable property, such as pressure or velocity of the fluid at a given point is constant over time.

Flow line: 

It is the path of an individual particle in a moving fluid.

Streamline:

It is a curve whose tangent at any point in the flow is in the direction of the velocity of the flow at that point. Streamlines and flow lines are identical for a steady flow.

Flow tube:

It is an imaginary bundle of flow lines bound by an imaginary wall. For a steady flow, the fluid cannot cross the walls of a flow tube. Fluids in adjacent flow tubes cannot mix.

Laminar flow/Streamline flow:

It is a steady flow in which adjacent layers of a fluid move smoothly over each other. A steady flow of river can be assumed to be a laminar flow.

Turbulent flow:

It is a flow at a very high flow rate so that there is no steady flow and the flow pattern changes continuously. A flooded river flow or a tap running very fast is a turbulent flow.