# Dictionary Definition

aerodynamics n : the branch of mechanics that
deals with the motion of gases (especially air) and their effects
on bodies in the flow [syn: aeromechanics]

# User Contributed Dictionary

## English

### Noun

aerodynamics- The science of the dynamics of bodies moving relative to gases, especially the interaction of moving objects with the atmosphere

#### Translations

- Croatian: aerodinamika
- German: Aerodynamik
- Hebrew: אוירודינמיקה
- Italian: aerodinamica
- Spanish: aerodinamica

# Extensive Definition

Aerodynamics is a branch of dynamics
concerned with studying the motion of air, particularly when it
interacts with a moving object. Aerodynamics is closely related to
fluid
dynamics and gas
dynamics, with much theory shared between them. Aerodynamics is
often used synonymously with gas dynamics, with the difference
being that gas dynamics applies to all gases. Understanding the
motion of air (often called a flow field) around an object enables
the calculation of forces and moments acting on the object. Typical
properties calculated for a flow field include velocity, pressure, density and temperature as a function of
position and time. By defining a control
volume around the flow field, equations for the conservation of
mass, momentum, and energy can be defined and used to solve for the
properties. The use of aerodynamics through mathematical analysis,
empirical approximation and wind tunnel experimentation form the
scientific basis for heavier-than-air
flight.

Aerodynamic problems can be identified in a
number of ways. The flow environment defines the first
classification criterion. External aerodynamics is the study of
flow around solid objects of various shapes. Evaluating the
lift
and drag on an
airplane,
the shock
waves that form in front of the nose of a rocket or the flow of air over a
hard drive head are examples of external aerodynamics. Internal
aerodynamics is the study of flow through passages in solid
objects. For instance, internal aerodynamics encompasses the study
of the airflow through a jet engine or
through an air
conditioning pipe.

The ratio of the problem's characteristic flow
speed to the speed of
sound comprises a second classification of aerodynamic
problems. A problem is called subsonic if all the speeds in
the problem are less than the speed of sound, transonic if speeds both below
and above the speed of sound are present (normally when the
characteristic speed is approximately the speed of sound), supersonic when the
characteristic flow speed is greater than the speed of sound, and
hypersonic when the
flow speed is much greater than the speed of sound. Aerodynamicists
disagree over the precise definition of hypersonic flow; minimum
Mach
numbers for hypersonic flow range from 3 to 12. Most
aerodynamicists use numbers between 5 and 8.

The influence of viscosity in the flow dictates
a third classification. Some problems involve only negligible
viscous effects on the solution, in which case viscosity can be
considered to be nonexistent. The approximations to these problems
are called inviscid
flows. Flows for which viscosity cannot be neglected are called
viscous flows.

## History

## Continuity assumption

Gases are composed of molecules which collide with one another and solid objects. If density and velocity are taken to be well-defined at infinitely small points, and are assumed to vary continuously from one point to another, the discrete molecular nature of a gas is ignored.The continuity assumption becomes less valid as a
gas becomes more rarefied. In these cases, statistical
mechanics is a more valid method of solving the problem than
aerodynamics.

## Laws of Conservation

Aerodynamic problems are solved using the conservation laws, or equations derived from the conservation laws. In aerodynamics, three conservation laws are used:- Conservation of mass: Matter is not created or destroyed. If a certain mass of fluid enters a volume, it must either exit the volume or increase the mass inside the volume. In a steady-state process mass cannot accumulate inside the volume and this law is expressed in the continuity equation.
- Conservation of momentum: Also called Newton's third law of motion. The initial momentum (mass times velocity) of a system must equal the final momentum of the system.
- Conservation of energy: Although it can be converted from one form to another, the total energy in a given system remains constant.

## Incompressible aerodynamics

An incompressible flow is characterized by a constant density despite flowing over surfaces or inside ducts. A flow can be considered incompressible as long as its speed is low. For higher speeds, the flow will begin to compress as it comes into contact with surfaces. The Mach number is used to distinguish between incompressible and compressible flows.#### Subsonic flow

Subsonic (or low-speed) aerodynamics is the study of inviscid, incompressible and irrotational aerodynamics where the differential equations used are a simplified version of the governing equations of fluid dynamics.. It is a special case of Subsonic aerodynamics.In solving a subsonic problem, one decision to be
made by the aerodynamicist is whether to incorporate the effects of
compressibility. Compressibility is a description of the amount of
change of density in the
problem. When the effects of compressibility on the solution are
small, the aerodynamicist may choose to assume that density is
constant. The problem is then an incompressible low-speed
aerodynamics problem. When the density is allowed to vary, the
problem is called a compressible problem. In air, compressibility
effects are usually ignored when the Mach number
in the flow does not exceed 0.3 (about 335 feet per second or 228
miles per hour or 102 meters per second at 60oF). Above 0.3, the
problem should be solved using compressible aerodynamics.

## Compressible aerodynamics

According to the theory of aerodynamics, a flow is considered to be compressible if its change in density with respect to pressure is non-zero along a streamline. In short, this means that, unlike incompressible flow, changes in density must be considered. In general, this is the case where the Mach number in part or all of the flow exceeds 0.3. The Mach .3 value is rather arbitrary, but it is used because gas flows with a Mach number below that value demonstrate changes in density with respect to the change in pressure of less than 5%. Furthermore, that maximum 5% density change occurs at the stagnation point of an object immersed in the gas flow and the density changes around the rest of the object will be significantly lower. Transonic, supersonic, and hypersonic flows are all compressible.#### Transonic flow

The term Transonic refers to a range of velocities just below and above the local speed of sound (generally taken as Mach 0.8–1.2). It is defined as the range of speeds between the critical Mach number, when some parts of the airflow over an aircraft become supersonic, and a higher speed, typically near Mach 1.2, when all of the airflow is supersonic. Between these speeds some of the airflow is supersonic, and some is not.#### Supersonic flow

Supersonic aerodynamic problems are those involving flow speeds greater than the speed of sound. Calculating the lift on the Concorde during cruise can be an example of a supersonic aerodynamic problem.Supersonic flow behaves very differently from
subsonic flow. Fluids react to differences in pressure; pressure
changes are how a fluid is "told" to respond to its environment.
Therefore, since sound is
in fact an infinitesimal pressure difference propagating through a
fluid, the speed of
sound in that fluid can be considered the fastest speed that
"information" can travel in the flow. This difference most
obviously manifests itself in the case of a fluid striking an
object. In front of that object, the fluid builds up a stagnation
pressure as impact with the object brings the moving fluid to
rest. In fluid traveling at subsonic speed, this pressure
disturbance can propagate upstream, changing the flow pattern ahead
of the object and giving the impression that the fluid "knows" the
object is there and is avoiding it. However, in a supersonic flow,
the pressure disturbance cannot propagate upstream. Thus, when the
fluid finally does strike the object, it is forced to change its
properties -- temperature, density, pressure, and Mach number
-- in an extremely violent and
irreversible fashion called a shock wave.
The presence of shock waves, along with the compressibility effects
of high-velocity (see Reynolds
number) fluids, is the central difference between supersonic
and subsonic aerodynamics problems.

#### Hypersonic flow

In aerodynamics, hypersonic speeds are speeds that are highly supersonic. In the 1970s, the term generally came to refer to speeds of Mach 5 (5 times the speed of sound) and above. The hypersonic regime is a subset of the supersonic regime. Hypersonic flow is characterized by high temperature flow behind a shock wave, viscous interaction, and chemical dissociation of gas.## Associated terminology

The incompressible and compressible flow regimes produce many associated phenomena, such as boundary layers and turbulence.#### Boundary layers

The concept of a boundary layer is important in many aerodynamic problems. The viscosity and fluid friction in the air is approximated as being significant only in this thin layer. This principle makes aerodynamics much more tractable mathematically.#### Turbulence

In aerodynamics, turbulence is characterized by chaotic, stochastic property changes in the flow. This includes low momentum diffusion, high momentum convection, and rapid variation of pressure and velocity in space and time. Flow that is not turbulent is called laminar flow.## Aerodynamics in other fields

further Automotive aerodynamics Aerodynamics is important in a number of applications other than aerospace engineering. It is a significant factor in any type of vehicle design, including automobiles. It is important in the prediction of forces and moments in sailing. It is used in the design of large components such as hard drive heads. Structural engineers also use aerodynamics, and particularly aeroelasticity, to calculate wind loads in the design of large buildings and bridges. Urban aerodynamics seeks to help town planners and designers improve comfort in outdoor spaces, create urban microclimates and reduce the effects of urban pollution. The field of environmental aerodynamics studies the ways atmospheric circulation and flight mechanics affect ecosystems. The aerodynamics of internal passages is important in heating/ventilation, gas piping, and in automotive engines where detailed flow patterns strongly affect the performance of the engine.## See also

- List of aerospace engineering topics
- List of engineering topics
- Automotive aerodynamics
- Aeronautics
- Fluid dynamics
- Aerostatics
- Nose cone design
- Bernoulli's principle
- Navier-Stokes equations
- Center of pressure
- Computational Fluid Dynamics
- Transonic flows.
- Supersonic flows.
- Hypersonic flows.
- Sound barrier

## References

## Further reading

General Aerodynamics- Fundamentals of Aerodynamics
- Aerodynamics for Engineers
- Illustrated Guide to Aerodynamics
- Introduction to Aerodynamics

Subsonic Aerodynamics

- Low-Speed Aerodynamics

Transonic Aerodynamics

- Fundamentals of Transonic Flow
- Transonic Aerodynamics

Supersonic Aerodynamics

- Elements of Aerodynamics of Supersonic Flows
- The Dynamics and Thermodynamics of Compressible Fluid Flow, Volume 1
- Modern Compressible Flow
- Elements of Gasdynamics
- Mathematical Theory of Compressible Fluid Flow
- Compressible Fluid Dynamics with Personal Computer Applications

Hypersonic Aerodynamics

- Hypersonic and High Temperature Gas Dynamics
- Hypersonic Inviscid Flow

History of Aerodynamics

- Progress in Flying Machines
- Aerodynamics: Selected Topics in the Light of Their Historical Development
- A History of Aerodynamics: And Its Impact on Flying Machines

Aerodynamics Related to Engineering

Ground Vehicles

- Race Car Aerodynamics: Designing for Speed
- Road Vehicle Aerodynamic Design

Fixed-Wing Aircraft

- Aerodynamics of Wings and Bodies
- Theory of Wing Sections: Including a Summary of Airfoil Data

Helicopters

- Principles of Helicopter Aerodynamics
- Helicopter Performance, Stability, and Control
- Basic Helicopter Aerodynamics: An Account of First Principles in the Fluid Mechanics and Flight Dynamics of the Single Rotor Helicopter

Missiles

- Missile Aerodynamics

Model Aircraft

- Model Aircraft Aerodynamics

Related Branches of Aerodynamics

Aerothermodynamics

- Basics of Aerothermodynamics
- Hypersonic Aerothermodynamics

Aeroelasticity

- Aeroelasticity
- An Introduction to the Theory of Aeroelasticity

Boundary Layers

- Boundary Layers
- Laminar Boundary Layers

Turbulence

- A First Course in Turbulence
- Turbulent Flows

## External links

- NASA Beginner's Guide to Aerodynamics
- Aerodynamics for Students
- Applied Aerodynamics: A Digital Textbook
- Aerodynamics and Race Car Tuning
- Aerodynamic Related Projects
- Supersonic wing design
- eFluids Bicycle Aerodynamics
- Application of Aerodynamics in Formula One (F1)
- Aerodynamics in Car Racing
- Aerodynamics of Birds
- Aerodynamics and dragonfly wings

aerodynamics in Asturian: Aerodinámica

aerodynamics in Azerbaijani: Aerodinamika

aerodynamics in Bosnian: Aerodinamika

aerodynamics in Bulgarian: Аеродинамика

aerodynamics in Catalan: Aerodinàmica

aerodynamics in Czech: Aerodynamika

aerodynamics in Danish: Aerodynamik

aerodynamics in German: Aerodynamik

aerodynamics in Modern Greek (1453-):
Αεροδυναμική

aerodynamics in Spanish: Aerodinámica

aerodynamics in Esperanto: Aerodinamiko

aerodynamics in Basque: Aerodinamika

aerodynamics in Persian: آیرودینامیک

aerodynamics in French: Aérodynamique

aerodynamics in Galician: Aerodinámica

aerodynamics in Korean: 공기역학

aerodynamics in Croatian: Aerodinamika

aerodynamics in Indonesian: Aerodinamika

aerodynamics in Italian: Aerodinamica

aerodynamics in Hebrew: אווירודינמיקה

aerodynamics in Latvian: Aerodinamika

aerodynamics in Hungarian: Aerodinamika

aerodynamics in Malay (macrolanguage):
Aerodinamik

aerodynamics in Dutch: Aerodynamica

aerodynamics in Japanese: 空気力学

aerodynamics in Norwegian: Aerodynamikk

aerodynamics in Polish: Aerodynamika

aerodynamics in Portuguese: Aerodinâmica

aerodynamics in Romanian: Aerodinamică

aerodynamics in Russian: Аэрогазодинамика

aerodynamics in Albanian: Aerodinamika

aerodynamics in Slovak: Aerodynamika

aerodynamics in Slovenian: Aerodinamika

aerodynamics in Serbian: Аеродинамика

aerodynamics in Finnish: Aerodynamiikka

aerodynamics in Swedish: Aerodynamik

aerodynamics in Vietnamese: Khí động lực
học

aerodynamics in Turkish: Aerodinamik

aerodynamics in Ukrainian: Аеродинаміка

aerodynamics in Chinese: 空气动力学

# Synonyms, Antonyms and Related Words

aerial photography, aeroballistics, aerogeology, aerography, aerology, aeromechanics, aeromedicine, aerometry, aeronautical
meteorology, aerophotography,
aerophysics,
aeroscopy, aerospace
research, aerostatics, air, atmosphere, aviation
technology, avionics,
barodynamics,
biodynamics,
climatology,
dynamics, fluid, fluid dynamics, gas, geodynamics, halogen gas,
hydrodynamics,
hydrostatics, inert
gas, kinematics,
kinesiology,
kinetics, magnetohydrodynamics,
meteorology,
myodynamics,
photometry, pneumatics, rocketry, supersonics, thermodynamics, zoodynamics