Aerodynamics is a branch of fluid dynamics concerned with the study of gas flows, first analysed by George Cayley in the 1800's. The solution of an aerodynamic problem normally involves calculating for various properties of the flow, such as velocity, pressure, density, and temperature, as a function of space and time. Understanding the flow pattern makes it possible to calculate or approximate the forces and moments acting on bodies in the flow. This mathematical analysis and empirical approximation form the scientific basis for heavier-than-air flight. This article or section should be merged with Fluid mechanics Fluid dynamics is the study of fluids (liquids and gases) in motion, and the effect of the fluid motion on fluid boundaries, such as solid containers or other fluids. ... Sir George Cayley (27 December 1773 - 15 December 1857) was an exuberant polymath from Brompton-by-Sawdon, near Scarborough in Yorkshire. ... Velocity (symbol: v) is a vector measurement of the rate and direction of motion. ... Pressure is the application of force to a surface, and the concentration of that force in a given area. ... Density (symbol: ρ - Greek: rho) is a measure of mass per unit of volume. ... Temperature is the physical property of a system which underlies the common notions of hot and cold; the material with the higher temperature is said to be hotter. ... In physics, as defined by Asimov, a force is that which can impose a change of velocity on a material body. ... In physics, the moment of force (often just moment, though there are other quantities of that name such as moment of inertia) is a quantity that represents the magnitude of force applied to a rotational system at a distance from the axis of rotation. ... This article refers to the tool of travel. ...

Aerodynamic problems can be classified 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. Lift consists of the negative product of all the aerodynamic forces normal to the direction of the external airflow. ... For a solid object moving through a fluid or gas, drag is the sum of all the aerodynamic or hydrodynamic forces in the direction of the external fluid flow. ... Fixed-wing aircraft is a term used to refer to what are more commonly known as aeroplanes in Commonwealth English (excluding Canada) or airplanes in North American English. ... In fluid dynamics, a shock wave is a nonlinear pressure wave. ... A Redstone rocket, part of the Mercury program A rocket is a vehicle, missile or aircraft which obtains thrust by the reaction to the ejection of fast moving exhaust gas from within a rocket engine. ... A Pratt and Whitney turbofan engine for the F-15 Eagle is tested at Robins Air Force Base, Georgia, USA. The tunnel behind the engine muffles noise and allows exhaust to escape. ... Note: in the broadest sense, air conditioning can refer to any form of heating, ventilation, and air-conditioning. ...

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 speed of sound c (from Latin celeritas, velocity) varies depending on the medium through which the sound waves pass. ... Subsonic has two possible meanings: A speed lower than the speed of sound is called subsonic. ... Transonic is an aeronautics term referring to a range of velocities just below and above the speed of sound. ... Any speed over the speed of sound, which is approximately 343 m/s, 1,087 ft/s, 761 mph or 1,225 km/h in air at sea level, is said to be supersonic. ... This article is about hypersonic speeds in aerodynamics. ... Mach number (Ma) is defined as a ratio of speed to the speed of sound in the medium in case. ...

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. The Pitch Drop Experiment at the University of Queensland. ...

Aerodynamic forces on aircraft

Forces on an aircraft (airfoil pictured)

One of the major goals of aerodynamics is to predict the aerodynamic forces on aircraft. The four forces on an aircraft: lift, weight, drag and thrust. ... The four forces on an aircraft: lift, weight, drag and thrust. ... An airfoil (in American English, or aerofoil in British English) is the shape of a wing or blade (of a propeller or ships screw) as seen in cross-section. ...

The four basic forces that act on a powered aircraft are lift, weight, thrust, and drag. Lift consists of the negative product of all the aerodynamic forces normal to the direction of the external airflow. ... Weight is the force exerted upon an object by virtue of its position in a gravitational field. ... For the land-speed record breaking car, see ThrustSSC and Thrust2 For the computer game, see Thrust (computer game) Thrust is a reaction force described quantitatively by Newtons Second Law when a system expels or accelerates mass in one direction to propel a vehicle in the opposite direction. ... For a solid object moving through a fluid or gas, drag is the sum of all the aerodynamic or hydrodynamic forces in the direction of the external fluid flow. ...

Weight is the force due to gravity and thrust is the force generated by the engine. Lift and drag are aerodynamic forces. Lift is defined as the aerodynamic force acting perpendicular to the relative airflow and drag is defined as the aerodynamic force acting parallel to the relative airflow. Lift is positive upwards and drag is positive rearwards.

Aerodynamics in other fields

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 small components such as hard drive heads. Civil engineers also use aerodynamics, and particularly aeroelasticity, to calculate wind loads in the design of large buildings and bridges. A small variety of cars, the most popular kind of automobile. ... Wooden sailing boat Sailing is motion across a body of water in a sailing ship, or smaller boat, powered by wind. ... Typical hard drives of the mid-1990s. ... In modern usage, civil engineering is a broad field of engineering that deals with the planning, construction, and maintenance of fixed structures as they related to earth, water, or civilization and their processes. ... No aircraft structure is completely rigid, so when it is subjected to aerodynamic forces it will normally deflect by a small amount. ... Wind is the quasi-horizontal movement of air (as opposed to an air current) caused by a horizontal pressure gradient force. ...

Continuity assumption

Gases are composed of molecules which collide with one another and solid objects. In aerodynamics, however, gases are considered to have continuous quantities. That is, properties such as density, pressure, temperature, 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. In science, a molecule is the smallest particle of a pure chemical substance that still retains its chemical composition and properties. ...

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. Statistical mechanics is the application of statistics, which includes mathematical tools for dealing with large populations, to the field of mechanics, which is concerned with the motion of particles or objects when subjected to a force. ...

Conservation laws

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.
• Conservation of momentum: Also called Newton's second law of motion
• Conservation of energy: Although it can be converted from one form to another, the total energy in a given system remains constant.

All aerodynamic problems are therefore solved by the same set of equations. However, they differ by the assumptions made in each problem. The equations become simpler as assumptions are made. Newtons laws of motion are the three scientific laws which Isaac Newton discovered concerning the behaviour of moving bodies. ...

Note that these laws are based on Newtonian Mechanics, they are not applicable in Einsteinian Mechanics (the latter taking into account Einstein's theory of relativity). Classical mechanics is a model of the physics of forces acting upon bodies. ... A simple introduction to this subject is provided in Special relativity for beginners Special relativity (SR) or the special theory of relativity is the physical theory published in 1905 by Albert Einstein. ... For other topics related to Einstein see Einstein (disambiguation). ... Albert Einsteins theory of relativity is a set of two scientific theories in physics: special relativity and general relativity. ...

Subsonic aerodynamics

In a subsonic aerodynamic problem, all of the flow speeds are less than the speed of sound. This class of problems encompasses nearly all internal aerodynamic problems, as well as external aerodynamics for general aviation aircraft, model aircraft, and automobiles. Subsonic has two possible meanings: A speed lower than the speed of sound is called subsonic. ...

In solving a subsonic problem, one decision to be made by the aerodynamicist is whether or not 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 problem. When the density is allowed to vary, the problem is called a compressible problem. In air, compressibility effects can be ignored when the Mach number in the flow does not exceed 0.3. Above 0.3, the problem should be solved using compressible aerodynamics.

Transonic aerodynamics

Transonic aerodynamic problems are defined as problems in which both supersonic and subsonic flow exist. Normally the term is reserved for problems in which the characteristic Mach number is very close to one.

Transonic flows are characterized by shock waves and expansion waves. A shock wave or expansion wave is a region of very large changes in the flow properties. In fact, the properties change so quickly they are nearly discontinuous across the waves. In fluid dynamics, a shock wave is a nonlinear pressure wave. ...

Transonic problems are arguably the most difficult to solve. Flows behave very differently at subsonic and supersonic speeds, therefore a problem involving both types is more complex than one in which the flow is either purely subsonic or purely supersonic.

Supersonic aerodynamics

Supersonic aerodynamic problems are those involving flow speeds greater than the speed of sound. Calculating the lift on the Concorde can be an example of a supersonic aerodynamic problem. Any speed over the speed of sound, which is approximately 343 m/s, 1,087 ft/s, 761 mph or 1,225 km/h in air at sea level, is said to be supersonic. ... The Aérospatiale-BAC Concorde supersonic transport (SST) was one of only two models of supersonic passenger airliners to have seen commercial service. ...

Supersonic flow behaves very differently from subsonic flow. The speed of sound can be considered the fastest speed that "information" can travel in the flow. Gas travelling at subsonic speed diverts around a body before striking it, it can be said to "know" that the body is there. Air cannot divert around a body when it is travelling at supersonic speeds. It continues to travel in a straight line until it reaches a shock wave and decelerates to subsonic speeds. Mathematically, supersonic flow is described by a hyperbolic partial differential equation while subsonic flow is described by an elliptic partial differential equation. A hyperbolic partial differential equation is usually a second-order partial differential equation of the form with . The wave equation: is such a hyperbolic equation. ... In mathematics, an Elliptic operator is a major type of differential operator P defined on spaces of complex-valued functions, or some more general function-like objects, such that the coefficients of the highest-order derivatives satisfy a positivity condition. ...

Another example of the difference between supersonic and subsonic flow is the behaviour in a convergent duct (known as a nozzle in subsonic flow and a diffuser in supersonic flow). Subsonic flow in a convergent duct accelerates and supersonic flow decelerates. Rocket Nozzle A nozzle is a mechanical device designed to control the characteristics of a fluid flow as it exits from an enclosed chamber into some medium. ... Diffuser is a pop punk band from the Long Island area that formed in 1994. ...

Hypersonic aerodynamics

Hypersonic aerodynamics are characterized by viscous interaction phenomena, that is, the viscosity of the flow significantly affects the external flow, including shock waves. The curved shock waves chemically alter the surrounding air or gas, creating a partially ionized plasma with their high temperatures (caused in part by significant aerodynamic heating of the body). "Hypersonic" is typically considered to refer to the Mach 5 and faster region of aircraft speed; however, some hypersonic phenomena can exist at speeds as low as Mach 3 (depending on the aircraft and the environment). The Pitch Drop Experiment at the University of Queensland. ... In fluid dynamics, a shock wave is a nonlinear pressure wave. ... This article is about plasma in the sense of an ionized gas. ... Aerodynamic heating is the heating of a solid body produced by passage of air or other gases over the body. ...

See also

• Aeronautics
• Fluid dynamics
• Bernoulli's equation
• Navier-Stokes equations
• Center of pressure