Aerodynamics and Its Application

AERODYNAMICS

Aerodynamics is the branch of physics dealing with the flow of air or other gases around a body in motion relative to it. Examples include the airflow around a bodies moving at speeds in the atmosphere (such as land vehicles, bullets, rockets and aircrafts) of gas in engines and furnaces, air conditioning of buildings, the decomposition of snow, the operation of air cushion vehicles such as hovercraft, wind loads on buildings and bridges, bird and insect flight, musical wind instruments and meteorology.

Air flowing past an aeroplane, or any other body, must be diverted from its original path, and such deflections lead to changes in the speed of the air. Aerodynamic forces depend on the body size, shape, velocity, density, compressibility, viscosity, temperature and pressure of the gas. At low speeds, flow around the body is streamlined or laminar and causes less drag. At higher velocities turbulence occurs, with fluctuating eddies and drag is much greater. For maximum efficiency, the aim is usually to design the shape of an object to produce a streamline flow with a minimum of turbulence in the moving air.

Pressure impulses radiate at the speed of sound ahead of the moving body. At supersonic velocities these impulses pile up producing a shock wave: the sonic boom. The behavior of aerosols or the pollution of the atmosphere by foreign particles is another aspect of aerodynamics.

Air has a density of 1.283Kg/m3 at sea level. This falls off with increasing altitude to about one-tenth at 64,000m, one-hundredth at 1,46,000m and one-millionth at 293,000m. Air is also viscous so that a solid body moving through it experiences drag not only from the direct displacement of the air molecules but also from the sheer resistance from the molecules slide over each other.

Speed is another factor considered in aerodynamics (subsonic supersonic and hypersonic speeds). At subsonic speeds aerodynamic drag force are proportional to the local air density, the dimensions of the surface on which air acts and the square of the velocity difference between the air and the surface, At supersonic speeds air passing through a pipe of varying cross-sections behaves in the reverse manner: a reduction in the duct diameter shows the down and increases its pressure. The waveform of a shockwave is unlike an ordinary wave that is not sinusoidal but flat fronted so that it instantly reaches its maximum amplitude. Above MACH 5(five times the speed of sound) these effects become so extreme that the gas molecules them selves may dissociate into atoms in an ionized state. The laws of a perfect gas no longer apply at that speeds and such flow is termed hypersonic.

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