The fluids can be classified into different types based on the variation of the fluid characteristics like velocity, density etc. Depending on the type of flow, the analysis method varies in fluid mechanics.

The different types of fluid flow are:

- Steady and Unsteady Flow
- Uniform and Non-Uniform Flow
- Laminar and Turbulent Flow
- Compressible and Incompressible Flow
- Rotational and Irrotational Flow
- One, Two and Three -dimensional Flow

## 1. Steady and Unsteady Flow

A flow is defined steady when its fluid characteristics like velocity, density, and pressure at a point do not change with time. A steady flow can be mathematically expressed as:

Where, V is the velocity of the fluid, āpā is the pressure and āJā is the density.

A flow is defined unsteady, when the fluid characteristics velocity, pressure and density at a point changes with respect to time. This can be mathematically expressed as:

## 2. Uniform and Non-Uniform Flow

Uniform flow is the type of fluid flow in which the velocity of the flow at any given time does not change with respect to space [Along the length of direction of flow].

A uniform flow can be mathematically expressed as:

A non-uniform flow is a type of fluid flow in which the velocity of the flow at any given time changes with respect to space. Mathematically, a non-uniform flow can be expressed as:

## 3. Laminar and Turbulent Flow

Laminar and Turbulent flow in a pipe flow is characterised based on Reynold number.

Laminar flow is defined as a type of flow in which the fluid particles move along a well-defined streamline or paths, such that all the streamlines are straight and parallel to each other. In a laminar flow, fluid particles move in laminas. The layers in laminar flow glide smoothly over the adjacent layer. The flow is laminar when the Reynolds number is more than 4000.

Turbulent flow is a type of flow in which the fluid particles move in a zig-zag manner. The movement in zig-zag manner results in high turbulence and eddies are formed. This results in high energy loss. The flow is turbulent when the Reynolds number is greater than 4000.

A fluid flow in a pipe, that has a Reynolds number between 2000 and 4000 is said to be in transition state.

## 3. Compressible and Incompressible Flows

A compressible flow is that type of flow in which the density of the fluid changes from one point to another point. This means the density is not constant.

**J not Constant**

Incompressible flow is that type of flow in which the density of the fluid is constant from one point to another. Liquids are generally incompressible and gases are compressible.

**J=Constant**

Where, J is a density of the fluid.

## 4. Rotational and Irrotational Flows

A type of flow in which the fluid particles rotate about their own axis while flowing along the streamlines is called a rotational flow. If the fluid particles while flowing along the streamline do not rotate about their own axis, then the flow is called irrotational flow.

## 5. One, Two and Three Dimensional Flows

One dimensional fluid flow is a fluid flow in which, the flow parameter such as velocity is expressed as a function of time and one space coordinates. That is,

**u = f(x,y), v=0; w=0;**

In this type, the velocity along y and z directions i.e. v and w are considered negligible.

Two-dimensional flow is that type of flow in which the velocity is a function of time and two rectangular space co-ordinates. The velocity of flow along the third direction is considered negligible. That is,

**u = f(x,y); v = g(x,y); w = 0;**

Three-dimensional flow is the type of flow in which the velocity is a function of time and three mutually perpendicular rectangular space coordinates (x, y, and z). That is,

**u = f(x,y,z); v = g(x,y,z); w = h(x,y,z)**

Also Read: Kinematics of Flow in Fluid Mechanics - Discharge and Continuity Equation