[Physics Class Notes] on Aerodynamics Pdf for Exam [2024]

The study of how gases interact with moving bodies is known as aerodynamics. Aerodynamics is mainly concerned with the forces of drag and lift induced by air flowing over and through solid bodies since air is the most common gas we experience.

Engineers use aerodynamic concepts in the design of a wide range of objects, including houses, bridges, and even soccer balls; however, the aerodynamics of a plane and automobiles are of primary concern.

Aerodynamics is used in the study of flight and aeronautics, which is the science of constructing and operating aircraft. Aeronautical engineers design aircraft that navigate through the Earth’s atmosphere using aerodynamic principles.

History of Aerodynamics

Modern aerodynamics only dates from the seventeenth century, but humans have been harnessing aerodynamic forces in sailboats and windmills for thousands of years, and pictures and stories of flight exist in recorded history, such as the Ancient Greek legend of Icarus and Daedalus.
Aristotle and Archimedes both used the terms continuum, drag, and pressure gradients in their writings.
Sir Isaac Newton, one of the first aerodynamicists, was the first person to establish a theory of air resistance in 1726.
Daniel Bernoulli, a Dutch-Swiss mathematician, published Hydrodynamica in 1738, in which he defined a fundamental relationship between friction, density, and flow velocity for incompressible flow that is now known as Bernoulli’s theory, which is used to calculate aerodynamic lift.
The more general Euler equations, which could be applied to both compressible and incompressible flows, were published by Leonhard Euler in 1757.
In the first half of the 1800s, the Euler equations were expanded to include the consequences of viscosity, resulting in the Navier–Stokes equations. The Navier-Stokes equations are the most general governing equations of fluid flow, but they are difficult to solve for all but the most basic shapes.
Sir George Cayley was the first to recognise the four aerodynamic forces of flight weight, lift, drag, and thrust, as well as their interrelationships, in 1799.
Francis Herbert Wenham built the first wind tunnel in 1871, which enabled precise measurements of aerodynamic forces.
Charles Renard, a French aeronautical engineer, was the first to predict the power needed for sustained flight in 1889.
Otto Lilienthal, who was the first to achieve great success with glider flights, was also the first to propose small, curved airfoils with high lift and low drag.
The Wright brothers flew the first powered aeroplane on December 17, 1903, based on the inventions and experiments conducted in their own wind tunnel.
The theory for flow properties before and after a shock wave was independently developed by Macquorn Rankine and Pierre Henri Hugoniot, while Jakob Ackeret led the initial work on calculating the lift and drag of supersonic airfoils.
Computational fluid dynamics began as an effort to solve for flow properties around complex objects and has quickly progressed to the point where entire aircraft can be designed using computer software, with wind tunnel and flight tests to confirm the computer predictions.
Designing aircraft for supersonic and hypersonic flight, as well as the desire to improve the aerodynamic efficiency of current aircraft and propulsion systems, continue to drive new aerodynamics research, while work on important problems in basic aerodynamic theory such as flow turbulence and the existence and uniqueness of analytical solutions to the Navier-Stokes equation continues.

Define Aerodynamic Principles

Weight, lift, thrust, and drag are the four principles of aerodynamics. These physics of flight and aircraft structures forces cause an object to travel upwards and downwards, as well as faster and slower.

Weight

There is a weight to all on Earth. Gravity pulls things down, which causes this force. A plane must be propelled in the opposite direction of gravity in order to travel. The force needed to push an object is determined by its weight. In comparison to a jumbo plane, a kite needs much less upward thrust.

Lift

A lift is a force that causes something to rise. It’s the force that’s the exact opposite of gravity. Anything that flies needs to be able to fly. An aircraft’s lift must be greater than its weight in order for it to climb. Since the hot air inside a hot air balloon is lighter than the air above it, it will provide a lift. The balloon is carried by hot air as it rises. A helicopter’s lift is provided by the rotor blades at the helicopter’s tip. The helicopter rises as a result of their movement through the air.

The wings of an aeroplane provide lift. It is the shape of an aeroplane’s wings that allows it to fly. The top of an aeroplane’s wing is curved, while the bottom is flat. Because of the form, air flows faster over the top than under the bottom. As a result, there is less air pressure on top of the wing. The wing, as well as the aeroplane to which it is connected, moves up as a result of this situation. Many aircraft employ the use of curves to adjust air pressure. This is how helicopter rotor blades work. A curved form also provides a lift for kites. This principle is used on sailboats as well. The sail of a boat is similar to a wing. That is what propels the sailboat forward.

Drag

A force that seeks to slow something down is called drag. It makes moving an object difficult. Walking or running through water is more difficult than walking or running through the air. This is due to the fact that water has a higher drag coefficient than air. The amount of drag is often affected by the shape of an object. When compared to flat surfaces, most round surfaces have less drag. Surfaces that are narrow have less drag than those that are wide. The more air that comes into contact with a surface, the more drag it produces.

Thrust

The power of thrust is the exact opposite of drag. Thrust is the forward movement of something. An aircraft must have more thrust than drag to keep going forward. A propeller could provide thrust to a small plane. Jet engines could provide propulsion to a larger plane. There is no thrust in a glider. It can only fly until the drag slows it down and forces it to land.

Law of Aerodynamics

< span>Problems in aerodynamics can be solved using fluid dynamics conservation laws according to the assumption of a fluid continuum. The three conservation law of aerodynamics are:

The law of conservation of mass or principle of mass conservation specifies that the mass of the system has to remain constant over time for every system closed to any transfer of matter and energy, as the mass of that system cannot change, so no additional quantity or removal can be made. The amount of mass is therefore maintained over time. The law imposes, though the mass may be rearranged within space or the associated entities may change in form, that mass can be neither created nor destroyed.

In a closed system where no matter is exchanged and external forces do not act, the total momentum is constant. Newton’s laws of motion imply that fact, known as the law for the conservation of momentum. Newton’s Second Law can be considered to apply the mathematical formulation of this principle. Only external forces, such as viscous forces and weight, can change the momentum in a flow. This can include both surface forces. The principle of momentum conservation can be expressed as a vector equation or divided into three scalar equations (x,y,z components).

The law of conservation of energy states that the total energy of an isolated system remains constant over time. Energy is neither produced nor lost within a flow, according to the energy conservation equation, and any addition or subtraction of energy to a volume in the flow is induced by heat transfer or work into and out of the region of interest. The law of conservation of energy states that a perpetual motion machine of the first kind cannot exist; no device can provide an infinite amount of energy to its surroundings without an external energy supply.

Together, these three laws are the known basis for Navier-Stokes equations. The Navier-Stokes equations have no proven analytical solution and are solved using computational techniques in modern aerodynamics. Since high-speed computing methods were not previously available, and because the computational cost of solving these complex equations is high now that they are, simplifications of the Navier-Stokes equations have been and continue to be used. The Euler equations are a series of related conservation equations that ignore viscosity and can be used in situations where viscosity is assumed to have a minor impact. Bernoulli’s equation is also a one-dimensional approach of both momentum and energy conservation equations.

Branches of Aerodynamics

Classification of Aerodynamics Based on the Flow Environment or Properties of the Flow:

A flow is said to be compressible if its density varies along a streamline, according to aerodynamic theory. This implies that, unlike incompressible flow, density variations are taken into account.
In general, when the Mach number in part or all of the flow reaches 0.3, this is the case where compressible flow occurs.
Although the Mach 0.3 value is arbitrary, it is used since gas flows with a Mach number less than that show density changes of less than 5%.
Furthermore, the overall density shift of 5% occurs at the object’s stagnation point, while density changes across the rest of the object would be much smaller.

The density of an incompressible flow is constant in both time and space. Although all real fluids are compressible, a flow is often approximated as incompressible if the impact of density changes on the measured results is minimal.
When the flow rates are slightly smaller than the speed of sound, this is more likely to be the case of incompressible flow.
At speeds equal to or above the speed of sound, compressibility has a greater impact.
The Mach number is used to determine whether incompressibility can be assumed otherwise, compressibility effects must be taken into account.

Classification of Aerodynamics Based on the Flow Speed Is Below, Near or Above the Speed of Sound.

Subsonic Flow

Subsonic or low-speed aerodynamics is the study of fluid motion in flow with speeds much lower than the speed of sound in the flow.
There are many types of subsonic flow, but when the flow is inviscid, incompressible, and irrotational, a unique case occurs. This is known as potential flow, and it allows the differential equations that describe the flow to be a simpler version of the fluid dynamics equations, allowing the aerodynamicist to choose from a variety of fast and simple solutions.
One of the decisions an aerodynamicist must make when solving a subsonic problem is whether or not to have compressibility effects.
The amount of change in density in a flow is referred to as compressibility. When the effects of compressibility on the solution are minor, it is possible to make the statement that density is constant.
The issue then becomes one of incompressible low-speed aerodynamics. The flow is said to be compressible when the density is allowed to vary.
When the Mach number in the flow is less than 0.3, compressibility effects are generally overlooked. The problem flow should be defined using compressible aerodynamics above Mach 0.3.

Transonic Flow

The word “transonic” refers to a range of flow velocities just below and above the Mach 0.8–1.2 local speed of sound.
It is defined as the speed range between the critical Mach number, at which some parts of the airflow over an aircraft become supersonic, and a higher speed, typically near Mach 1.2, at which the entire airflow becomes supersonic.

Supersonic Flow

Flow speeds higher than the speed of sound are referred to as supersonic flow.
Subsonic and supersonic flow behave very differently. Pressure changes are how a fluid is told to respond to its environment.
As a result, since sound is an infinitesimal pressure difference propagating through a fluid, the speed of sound in that fluid can be considered the fastest rate at which information can propagate through the flow.
The fluid builds up a stagnation pressure in front of the object as it collides with it, bringing the moving fluid to a halt. < /span>
This pressure disruption will spread upstream in a subsonic fluid, altering the flow pattern ahead of the object and giving the impression that the fluid is aware of its presence by shifting its movement and flowing around it.
However, in a supersonic flow, the pressure disturbance cannot travel upstream. As a result, when the fluid approaches the object, it collides with it, forcing the fluid to change its properties such as temperature, density, pressure, and Mach number in a violent and irreversible manner known as a shock wave.
The central difference between the supersonic and subsonic aerodynamics regimes is the presence of shock waves, as well as the compressibility effects of high-flow velocity fluids.

Hypersonic Flow

Hypersonic speeds are extremely supersonic speeds in aerodynamics.
The term came to be used to describe speeds of Mach 5 and higher, which are 5 times the speed of sound.
A subset of the supersonic regime is the hypersonic regime.
High-temperature flow behind a shock wave, viscous interaction, and chemical dissociation of gas defines the hypersonic flow.

In this article, we have discussed what is aerodynamics, the history of aerodynamics, principles of aerodynamics, the law of aerodynamics and branches of aerodynamics.

Conclusion

Aerodynamics is a branch of physics that studies the motion of air and other gaseous fluids, as well as the forces that act on objects moving through them. Aerodynamics aims to clarify the concepts that control the flight of aircraft, rockets, and missiles in particular. It also involves the design of cars, high-speed trains, and ships, as well as the construction of structures such as bridges and tall buildings to assess their wind resistance.