‘Fluid Flow’ is a term used to denote the flow of a fluid through a pipe (or any other structure). It is applied in many disciplines of engineering and technology.

Fluid dynamics is a branch of fluid mechanics that deals with the study of fluid flow.

## Types of Fluid Flow:

Based on flow characteristics, fluid flow can be broadly classified into two types:

### Laminar Flow:

A fluid flow is said to be laminar, if each particle of the fluid follows the path of its preceding particle.

In laminar flow, individual fluid particles do not cross each other. They move in regular paths in an orderly manner.

The fluid particles move smoothly in layers (laminae), one over the other.

A good example of laminar flow is the flow of blood through the arteries and veins of the human body. Another example is the flow of oil through a thin tube.

### Turbulent Flow:

In turbulent flow, fluid particles move in a zig-zag and haphazard way. They do not follow any regular pattern while flowing.

Individual fluid particles cross one another and exhibit irregular energy losses.

A good example of turbulent flow is the flow of river water. River water does not follow any regular flow pattern. It moves in a zig-zag and haphazard manner.

## Reynolds Number:

Reynolds number (denoted by ‘Re’) is a dimensionless number used to determine whether the flow of a fluid is laminar or turbulent. Reynold’s number is given by the following equation:

where,

ρ → Density of the fluid in kg/m^{3}

u → Mean Velocity of the fluid in m/s

D → Diameter of the pipe

μ → Dynamic viscosity of the fluid in Ns/m^{2}

ν → Kinematic viscosity of the fluid in m^{2}/s

### Determination of flow regime using Reynolds Number:

Reynolds number (Re) can be used to find the type of flow of a fluid.

- If Re < 2300, the fluid flow is said to be laminar.
- If Re > 4000, the fluid flow is turbulent.
- If 2300 < Re < 4000, the fluid flow is unstable i.e., the flow may become either laminar or turbulent.