Fluid Flow - Definition, Types, Example, FAQs

Fluid flow is a topic of fluid mechanics that deals with the subject of fluid dynamics. Let us understand a fluid flow process by answering questions like what is fluid, what is the meaning of fluid, what is the meaning of flow, and what are the types of fluid and types of flow.

What is Fluid?

Fluid is the matter of substances that do not have any fixed shape and are subjected to external pressure. The main feature of a fluid is its flowing ability. Now, let's see What is Fluid Flow?

Define fluid flow

A Fluid flow is known as the movement of a fluid from one point to the other. Fluid flow includes a fluid motion due to some unbalanced force. Until external unbalanced forces are applied to the motion of a fluid, a fluid will continue its motion.

According to the natural properties of a fluid, there are different types of fluid. Let's discuss them in detail.

Ideal Fluid:

An ideal fluid is defined as a fluid that cannot be compressed and also does not contain any viscosity. This is an imaginary fluid used only for mathematical calculations. Other than that, this fluid does not exist in reality. They have a constant density. They possess irrotational motion which has a smooth flow. They do not have any internal friction and have a steady flow.

Real Fluid:

All a fluids of the real world which contain viscosity and can be compressed to some extent are known as real fluids. They are also called practical fluids.

Real Fluid examples- Water, oil.

Newtonian fluid:

A Newtonian fluid is defined as a fluid which obeys the laws of Newton of Viscosity, where the shear stress is directly proportional to the velocity gradient.

Newtonian fluid examples- Water and Gasoline.

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Non-Newtonian fluid:

These fluids are opposite to Newtonian fluid. This fluid does not obey the laws of Newton of Viscosity. Theor viscosity changes with applied shear rate.

Non Newtonian fluid examples- Ketchup, toothpaste, blood.

Incompressible fluid:

When a fluid is subjected to any kind of external force, the density properties of a fluid does not change, this kind of fluid is known as incompressible fluid. Incompressible fluid example- Water, oil.

Compressible fluid:

When a fluid is subjected to any kind of external force, the density properties of a fluid will change and this kind of fluid is known as compressible fluid.

Compressible fluid examples- Natural gas, steam, air.

Superfluids:

It is a special phase of matter with zero viscosity that can flow without losing any energy. It has the ability to flow through tiny pores without resistance.

Superfluids examples- Liquid helium at very low temperatures

Plasma:

It is the fourth state of matter. An ionized gas where atoms are split into free electrons and ions, making it highly conductive.

Plasma examples- Stars (like the Sun), fluorescent lights, and plasma TVs.

Classification of Fluid

a fluid flow is categorized into different types considering different properties like steadiness, viscosity, compressibility, rotational property, and so on. They are categorized as below-

Based on their steadiness:

The velocity of a fluid decides the steadiness of a fluid flow.

• Steady flow: When the velocity of a fluid is constant, a fluid flow is found to be steady.
• Unsteady flow: When the velocity of a fluid varies from time to time, a fluid flow is found to be unsteady.

Based on their Viscosity:

a fluid is classified into viscous and non-viscous fluid.

• Viscous fluid: The term Viscosity is known as the measurement of a fluid thickness and a fluid with the viscosity is known as viscous fluid.
• Non-Viscous Fluid: A fluid having no viscosity is known as non viscous fluid.

Based on their compressibility:

On the basis of Mach number, flows are classified into compressible and incompressible fluid.

• Incompressible fluid flow has the Mach number M < 0.3
• Compressible fluid flow has the Mach number M between 0.3 to 1

Equation of fluid flow

The mass flow rate of a fluid flow is defined as the rate of massive fluid movement through a unit area. It is considered to be movement of mass of fluid per unit time.

Mathematically, the mass flow rate of a fluid can be written as

$$
M=\rho A V,
$$

where,

• $\rho$ denotes the density of a fluid
• A denotes the area of a fluid cross-section
• V represents the velocity of a fluid flow

Thus, the equation infers that the mass flow rate of fluid is proportional to density, area, and velocity of a fluid.

Applications of Fluid Statics in Real Life:

There are many applications of fluid statics in real life, the main application is it is used in the calculation and measurement of pressure of liquid in the field of hydrostatics like finding the pressure of floating and submerged bodies, pressure of water flow in water dams and gates, and water flow pressure in some liquid storage tanks of homes.

Applications of Fluid Dynamics in Real Life

There are huge applications in fluid dynamics, Let us discuss the few applications below:

• It is used to calculate and find the different types of forces and moments in the field of aircraft,
• It is used to determine the mass flow rate of petroleum or other gases through pipelines.
• Even they are used to predict weather patterns,
• It is used to understand and analyse the nebulae in interstellar space
• The use of fluid dynamics also plays a role in modeling different fission weapon detonations.