What Beginners Should Know About Fluid Mechanics!

Have you ever wondered what makes rivers flow, aeroplanes fly, or speedboats cut through the waves? The answer lies in fluid mechanics, which studies the behaviour of different fluids. In this article, we'll look at the basics of fluid mechanics so you can understand how fluids work and how they affect our everyday lives.

What is Fluid Mechanics?

Fluids do not have a shape, so they only interact with solid objects, i.e. containers they are kept in. These fluids are either stationary or moving in these containers (buckets, pipes, reservoirs, etc.). The fluids exert certain forces on the containers, either static or dynamic. In addition to that, there are external forces that may affect the behaviour of the fluid.

Fluid mechanics is a branch of physics that deals with the behaviour of fluids under external forces such as gravity, pressure, or shear stress. The goal of fluid mechanics is to understand and predict the behaviour of fluids to design efficient systems and structures.

There are many different fluid mechanics problems, but they can all be divided into two main categories: 

• Static: Where we deal with fluids at rest
• Dynamic: Where we deal with fluids in motion

One of the most important concepts in fluid mechanics is Bernoulli's principle, which states that the pressure decreases and the speed increases when a fluid flows through a constriction. This principle can explain different phenomena, such as why planes can fly and how blood flows through arteries.

Branches of Fluid Mechanics

There are three main branches of fluid mechanics:

• Hydraulics:  Deals with the flow of liquids
• Pneumatics:  Deals with the flow of gases
• Hydrodynamics: Deals with the motion of fluids

Within these branches, further sub-branches focus on specific aspects of fluid mechanics, such as transport phenomena or thermodynamics.

Types of Fluids

In fluid mechanics, fluids are commonly classified based on their physical properties, such as viscosity, density, and compressibility. The following are the main types of fluids:

• Newtonian fluids: Fluids whose viscosity is independent of the stress applied. Examples are water, air, and most liquids.
• Non-Newtonian fluids: Fluids whose viscosity changes with the stress applied. Examples are honey, ketchup, and blood.
• Ideal fluids: Fluids are considered to have zero viscosity and are incompressible. They are used as a theoretical model for studying fluid dynamics.
• Real fluids: Fluids with viscosity and other real fluid properties, like liquids and gases. They deviate from the behaviour of ideal fluids and are used to study practical fluid mechanics problems.
• Compressible fluids: Fluids whose density changes with pressure. Examples are gases.
• Incompressible fluids: Fluids whose density is constant and does not change with pressure. Examples are liquids.

Properties of Fluids

When measuring a system's performance, we need to set certain parameters to estimate the performance. In this instance, to understand how fluids behave, we need certain parameters to understand the state of the fluid at hand.

There are three primary properties of fluids that are important to understand: density, viscosity, and surface tension.

• Pressure: A measure of the force exerted per unit area. A scalar quantity is a force exerted on a unit area (N/m2). 
• Pressure is exerted in all directions, and the pressure at a point in the fluid is equal in all directions.
• In a fluid at rest, pressure is transmitted throughout the fluid without any loss or increase, known as Hydrostatic Pressure.
• Density: measures how much mass a fluid has in a given volume. 
• It is usually expressed in grams per cubic centimetre (g/cm3).
• The denser fluid is, the more mass it has in a given volume.
• Viscosity: A measure of a fluid's resistance to flow
• The more viscous a fluid is, the more resistant it is to flow.
• Viscosity is usually expressed in terms of centipoise (cP).
• Surface tension: A measure of the forces that act on the molecules at the surface of a liquid
• These forces cause the molecules at the surface to be pulled together, which gives liquids their characteristic shape.
• Surface tension is usually expressed in dynes per centimetre (dyn/cm).

• Flow Rate: Flow rate measures the amount of fluid that passes through a given cross-sectional area per unit of time. 
• It is usually expressed in units of volume per unit of time, such as litres per second (L/s) or cubic meters per second (m3/s).
• In fluid mechanics, the flow rate is an important parameter in describing fluid flow, and it is used to calculate the volume of fluid that passes through a pipe or channel over a given period.
• Flow rate can vary along the length of a pipe or channel, and it can also change with time due to fluid velocity or cross-sectional area changes.
• Understanding and predicting changes in flow rate is an important aspect of fluid mechanics and is used in various applications such as water supply, hydraulic systems, and industrial processes.

Applications of Fluid Mechanics:

Fluid mechanics is vital in many industries, including aerospace, automotive, chemical, civil, and mechanical engineering.

• Engineers use fluid dynamics principles in fluid mechanics to design and analyse systems involving fluids.
• These systems include aircraft wings and car bodies to blood vessels and pipes. In addition to its industrial applications, fluid mechanics plays a role in our everyday lives.
• For example, the Bernoulli principle governing air flow helps us understand how an aeroplane stays in the air and how a curved road affects traffic.
• There are various areas of applications for CFD:
• Heat Transfer flows: Understanding the transfer of heat between fluids and solids in a system
• For example, heat exchangers, electronics cooling, etc.
• Multiphase flows: Understanding the flows in the presence of more than one phase of fluid (solid-liquid, liquid-liquid, gas-liquid)
• For example, oil mixed with water, condensation of steam, etc.
• Combustion flows: Understanding the implications of combustion for a flow
• For example, flow in IC engines, aircraft combustors, etc
• Aerodynamics: Understanding the distribution of pressure and shear stress on a body to study the resultant lift and drag forces
• For example, cars moving on a highway, aeroplane wings, etc
• Fluid Mechanics is a vast field of study, which enables an engineer to study fluids well so they can make decisions to facilitate for best performance of the system they want to design

Conclusion

With the right foundation, you can unlock a world of fascinating applications and use some powerful tools that can help solve many complex problems. 

So why not get started today? Enroll with Skill-Lync to upskill in computational fluid dynamics and CAD softwares like CATIA, Solidworks, Ansys Workbench etc. and become a job-ready mechanical engineer.