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: . The willingness to question previously held truths and search for new answers resulted in a period of major scientific advancements, now known as the Scientific Revolution. ... A subset of the phases of matter, fluids include liquids, gases, plasmas and, to some extent, plastic solids. ... A solid is a state of matter, characterized by a definite volume and a definite shape (i. ... Pressure is the application of force to a surface, and the concentration of that force in a given area. ... Stress has different meanings in different fields: Stress (physics); see also tensile stress, shear stress and pressure. ...

For a gas the magnitude of the compressibility depends strongly on whether the process is adiabatic or isothermal, while this difference is small in a solid. This article covers adiabatic processes in thermodynamics. ... An isothermal process is a thermodynamic process in which the temperature of the system stays constant; ΔT = 0. ...

The inverse of the compressibility is called the bulk modulus, often denoted K. That page also contains some examples for different materials. The bulk modulus K of a fluid or solid is the inverse of the compressibility: where p is pressure and V is volume. ...

Compressibility is an important notion in aerodynamics. At low speeds, the compressibility of air is not important for aircraft design, but as the airflow nears and exceeds the speed of sound, a host of new aerodynamic effects become important in the design of aircraft. These effects, often several of them at a time, made it very difficult for World War II era aircraft to reach speeds much beyond 500mph. Aerodynamics is a branch of fluid dynamics concerned with the study of gas flows, first analysed by George Cayley in the 1800s. ... An aircraft is any machine capable of atmospheric flight. ... The speed of sound c (from Latin celeritas, velocity) varies depending on the medium through which the sound waves pass. ... World War II was a truly global conflict with many facets: immense human sacrifice, fierce indoctrinations, and the use of new, extremely devastating weapons—the atom bomb being the ultimate. ...

Some of the minor effects include changes to the airflow that lead to problems in control. For instance, the P-38 Lightning had a particular problem in high speed dives that led to a noce-heavy condition. Pilots would enter dives, and then find that they could no longer control the plane, which continued to nose over until it crashed. Adding a "dive flap" beneath the wing to upset the airflow cured the problem. P-38 may also refer to the P-38, an army-issue can opener, or to the Walther P38 handgun The Lockheed P-38 Lightning was one of the most important American fighters of the Second World War. ...

A similar problem effected some models of the Supermarine Spitfire. At high speeds the ailerons could apply more torque than the Spitfire's thin wings could handle, and the entire wing would twist in the opposite direction. This meant that the plane would roll in the direction opposite to what the pilot expected, and led to a number of accidents. This wasn't noticed until later model Spitfires like the Mk.IX started to appear, because earlier models weren't fast enough. This was solved by adding considerable strength to the wings, and was wholly cured when the Mk.XIV was introduced. The Supermarine Spitfire was a single seat fighter used by the RAF and many Allied countries in World War II. The Spitfires elliptical wings gave it a very distinctive look; their thin cross-section gave it speed; the brilliant design of Chief Designer R.J. Mitchell and his successors... Aileron location on a Piper PA-28. ...

The Messerschmitt Bf 109 and Mitsubishi Zero had the exact opposite problem, the controls were too weak. At higher speeds the pilot simply couldn't move the controls because there was too much airflow over the control surfaces. The planes would become difficult to manoeuvre, and at high enough speeds even less manoeuvrable aircraft could out-turn them. (Bf 109 was the official Reichsluftfahrtministerium designation, though some late-war aircraft actually carried the Me 109 designation stamped onto their aircraft type plates. ... Mitsubishi A6M5 Zero Model 52 The Mitsubishi A6M was a light-weight carrier-based fighter aircraft employed by the Imperial Japanese Navy from 1940 to 1945. ...

Finally, another common problem that fits into this category is flutter. At some speeds the airflow over the control surfaces will become turbulent, and the controls will start to flutter. If the speed of the fluttering is close to a harmonic of the control's movement, the resonance could break the control off completely. This was a serious problem on the Zero. When they first encountered problems with the poor control at high speed they addressed it with a new style of control surface with more power. However this introduced a new resonant mode, and a number of planes disappeared before this was discovered. Flutter: In electronics, rapid variation of signal parameters, such as amplitude, phase, and frequency. ... sdf f sdf sd ... In physics, resonance is the tendency of a system to absorb more oscillatory energy when the frequency of the oscillations matches the systems natural frequency of vibration (its resonant frequency) than it does at other frequencies. ...

All of the items above are often talked about when the term "compressibility" is used, but in a manner of speaking, they are all incorrectly used. From a strictly aerodynamic point of view, the term should refer only to those effects arising as a side effect of the changes in airflow from an incompressible fluid (similar in effect to water) to compressible fluid (acting as a gas) as you approach the speed of sound. There are two effects in particular, wave drag and critical mach. Wave drag is an aerodynamics term that refers to a sudden and very powerful form of drag that appears on aircraft flying at high-subsonic speeds. ... Critical mach is a aeronautics term that refers to the speed at which some of the airflow on a wing becomes supersonic. ...

Wave drag is a sudden rise in drag on the aircraft, caused by air building up in front of it. At lower speeds this air has time to "get out of the way", guided by the air in front of it that is in contact with the aircraft. But at the speed of sound this can no longer happen. Air which was previously following the streamline around the aircraft now hits it directly. The amount of power needed to overcome this effect is considerable. ok here it is for the simple folk streamlining is the shaping of an object so it has less air resistance. ...

At the speed of sound the way that lift is generated changes dramatically, from being dominated by Bernoulli's principle to forces generated by shock waves. Since the air on the top of the wing is travelling faster than on the bottom, due to Bernoulli effect, at speeds close to the speed of sound the air on the top of the wing will be accelerated to supersonic. When this happens the distribution of lift changes dramatically, typically causing a powerful nose-down trim. Since the aircraft normally approached these speeds only in a dive, pilots would report the aircraft attempting to nose over into the ground. ěūūÖÂÄËBernoullis principle states that in [[fluid]] flow, an increase in [[velocity]] occurs simultaneously with decrease in [[pressure]]. It is named for the [[Netherlands|Dutch]]/[[Switzerland|Swiss]] mathematician/scientist [[Daniel Bernoulli]], though it was previously understood by [[Leonhard DOGGIE!!!!!!]] relies upon the pressure differential above and below a wing. ... In fluid dynamics, a shock wave is a nonlinear pressure wave. ...

All of these effects have adverse effects on the control or performance of the plane. For this reason it's common to see references to aircraft that suffer from compressibility. The P-38 and Zero are particularly common examples, although in fact they are both bad ones.

Thermodynamics

The term "compressibility" is also used in thermodynamics to describe the deviance in the thermodynamic properties of a real gas from those expected from an ideal gas. The compressibility factor is defined as This article needs to be cleaned up to conform to a higher standard of quality. ... Here is a partial list of thermodynamic properties of fluids: temperature [K] density [kg/m3] specific heat at constant pressure [J/kg·K] specific heat at constant volume [J/kg·K] dynamic viscosity [N/m²s] kinematic viscosity [m²/s] thermal conductivity [W/m·K] thermal diffusivity [m²/s] volumetric... An ideal gas (also called a perfect gas) is a hypothetical fluid consisting of particles that are identical to each other, occupy negligible volume and undergo perfect elastic collisions with each other, with no intermolecular forces and no intramolecular storage of energy, as opposed to a real gas, a gas... An ideal gas or perfect gas is a hypothetical gas consisting of identical particles of negligible volume, undergoing perfectly elastic collisions, with no intermolecular forces and no intramolecular storage of energy. ...

where P is the pressure of the gas, T is its temperature, and is its molar volume. In the case of an ideal gas, the compressibility factor Z is equal to unity, and the familiar ideal gas law is recovered: Pressure is the application of force to a surface, and the concentration of that force in a given area. ... 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 chemistry, the molar volume of a substance is the ratio of the volume of a sample of that substance to the amount of substance (usually in mole) in the sample. ... The ideal gas law or equation is the equation of state of an ideal gas. ...

Z can, in general, be either greater or less than unity for a real gas.

The deviation from ideal gas behavior tends to become particularly significant (or, equivalently, the compressibility factor strays far from unity) near the critical point, or in the case of high pressure or low temperature. In these cases, an alternative equation of state better suited to the problem must be utilized to produce accurate results. Chemistry In chemistry, a critical point is the conditions ( temperature, pressure) at which the liquid state of the matter ceases to exist. ... In physics and thermodynamics, an equation of state is a constitutive equation describing the state of matter under a given set of physical conditions. ...