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Encyclopedia > Aerodynamics

A profile of an aircraft wing.

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. Sound is a vibration that travels through an elastic medium as a wave. ... 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. ... A United States Navy F/A-18E/F Super Hornet in transonic flight. ... Boeing X-43 at Mach 7 In aerodynamics, hypersonic speeds are speeds that are highly supersonic. ... An F/A-18 Hornet breaking the sound barrier. ...

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. For other uses, see Viscosity (disambiguation). ... A fluid flow where viscous (friction) forces are small in comparison to inertial forces is said to be inviscid. ...

## Aerodynamics in other fields GA_googleFillSlot("encyclopedia_square");

Further information: Automotive aerodynamics

Aerodynamics is important in a number of applications other than aerospace engineering. Automotive aerodynamics is the study of the aerodynamics of road vehicles. ...

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. 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 affects 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. â€œCarâ€ and â€œCarsâ€ redirect here. ... For either of the songs named Sailing, see Sailing (song). ... Typical hard drives of the mid-1990s. ... Taipei 101, the worlds tallest building as of 2004. ... Aeroelasticity is the science which studies the interaction among inertial, elastic, and aerodynamic forces. ... For other uses, see Wind (disambiguation). ...

## Continuity assumption

Bernoulli's principle: Gases are composed of molecules which collide with one another and solid objects. If j 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. 3D (left and center) and 2D (right) representations of the terpenoid molecule atisane. ...

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 probability theory, 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.

Newtons laws of motion are the three scientific laws which Isaac Newton discovered concerning the behaviour of moving bodies. ...

## Boundary layer

The concept of boundary layer is important in most aerodynamic problems. The viscosity and fluid friction in the air is usually important only in this thin layer. This principle makes aerodynamics much more tractable mathematically and also intuitively. In physics and fluid mechanics, a boundary layer is that layer of fluid in the immediate vicinity of a bounding surface. ...

## Low-speed aerodynamics

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.[1]. It is a special case of Subsonic aerodynamics. Viscosity is a measure of the resistance of a fluid to deformation under shear stress. ... Fluid Dynamics Compressibility (physics) is a measure of the relative volume change of fluid or solid as a response to a pressure (or mean stress) change: . For a gas the magnitude of the compressibility depends strongly on whether the process is adiabatic or isothermal, while this difference is small in... In fluid mechanics, an irrotational vector field is a vector field whose curl is zero. ... In mathematics, a differential equation is an equation in which the derivatives of a function appear as variables. ... Fluid dynamics is the sub-discipline of fluid mechanics dealing with fluids (liquids and gases) in motion. ...

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 low-speed aerodynamics 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. For other uses, see Density (disambiguation). ... An F/A-18 Hornet breaking the sound barrier. ...

## 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 most unpowered and propeller driven aircraft, model aircraft, and automobiles. Notable exceptions are propellers and rotors whose tip speeds can become transonic or even supersonic. Sound is a vibration that travels through an elastic medium as a wave. ... For other uses, see Propeller (disambiguation). ... â€œFlying Machineâ€ redirects here. ... A Die Cast Boeing 747-800 static model. ... â€œCarâ€ and â€œCarsâ€ redirect here. ...

## Supersonic aerodynamics

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. A United States Navy F/A-18E/F Super Hornet in transonic flight. ... For other uses, see Concorde (disambiguation). ...

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 infinitesmal 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 Gas 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. Sound is a disturbance of mechanical energy that propagates through matter as a wave. ... Sound is a vibration that travels through an elastic medium as a wave. ... Total Pressure redirects here. ... For other uses, see Temperature (disambiguation). ... For other uses, see Density (disambiguation). ... This article is about pressure in the physical sciences. ... An F/A-18 Hornet breaking the sound barrier. ... In thermodynamics, a reversible process (or reversible cycle if the process is cyclic) is a process that can be reversed by means of infinitesimal changes in some property of the system. ... Introduction The shock wave is one of several different ways in which a gas in a supersonic flow can be compressed. ... In fluid mechanics, the Reynolds number is the ratio of inertial forces (vsÏ) to viscous forces (Î¼/L) and consequently it quantifies the relative importance of these two types of forces for given flow conditions. ...

## References

1. ^ Katz, Joseph (1991). Low-speed aerodynamics: from wing theory to panel methods, McGraw-Hill series in aeronautical and aerospace engineering. McGraw-Hill.

This page aims to list all articles related to the specific discipline of aerospace engineering. ... This page aims to list all topics related to the broad field of engineering. ... Automotive aerodynamics is the study of the aerodynamics of road vehicles. ... Six F-16 Fighting Falcons with the U.S. Air Force Thunderbirds aerial demonstration team fly in delta formation in front of the Empire State Building. ... Fluid dynamics is the sub-discipline of fluid mechanics dealing with fluids (liquids and gases) in motion. ... Aerostatics is the study of gases that are not in motion. ... Given the problem of the aerodynamic design of the nose cone section of any vehicle meant to travel through a compressible fluid medium (such as a rocket or aircraft), the main problem at hand is the determination of the nose cone geometrical shape. ... Bernoullis butt states that for an ideal [[pee] (low speed air is a good approximation), with no hard work being performed on the fluid, an increase in stream occurs simultaneously with decrease in pressure or a change in the fluids pee pee energy. ... The Navier-Stokes equations, named after Claude-Louis Navier and George Gabriel Stokes, are a set of equations which describe the motion of fluid substances such as liquids and gases. ... The Center of Pressure (or CoP) is the point on a body where the sum of the total pressure acts. ... A computer simulation of high velocity air flow around the Space Shuttle during re-entry. ... Transonic is an aeronautics term referring to a range of velocities just below and above the speed of sound. ... A United States Navy F/A-18E/F Super Hornet in transonic flight. ... Boeing X-43 at Mach 7 In aerodynamics, hypersonic speeds are speeds that are highly supersonic. ... U.S. Navy F/A-18 at transonic speed. ...

Results from FactBites:

 Beginner's Guide to Aerodynamics (456 words) Aerodynamics is the study of forces and the resulting motion of objects through the air. Aerodynamics affects the motion of a large airliner, a model rocket, a beach ball thrown near the shore, or a kite flying high overhead. Because aerodynamics involves both the motion of the object and the reaction of the air, there are several pages devoted to basic gas properties and how those properties change through the atmosphere.
 Science of Cycling: Aerodynamics: page 1 (767 words) While newer bicycles are being designed with better aerodynamics in mind, the human body is simply not well designed to slice through the air. Aerodynamic drag consists of two forces: air pressure drag and direct friction (also known as surface friction or skin friction). On a flat road, aerodynamic drag is by far the greatest barrier to a cyclist's speed, accounting for 70 to 90 percent of the resistance felt when pedaling.
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