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F/A-18 demonstrating singularity effect
F/A-18 demonstrating singularity effect

The Prandtl-Glauert singularity (sometimes referred to as a "vapor cone"), is the point at which a sudden drop in air pressure occurs, and is generally accepted as the cause of the visible condensation cloud that often surrounds an aircraft traveling at transonic speeds, though there remains some debate. WikipediaWikiProject Aircraft. Please see WikipediaWikiProject Aircraft/page content for recommended layout Ludwig Prandtl ( 4 February 1875 &ndash 15 August 1953) was a German Physicist. Hermann Glauert, FRS (b 4 October 1892 in Sheffield, d 6 August 1934 in Aldershot) was a British Condensation is the change of the physical state of aggregation (or simply state of matter from gaseous phase into liquid phase Transonic is an Aeronautics term referring to a range of velocities just below and above the Speed of sound (about mach 0 It is an example of a mathematical singularity in aerodynamics. In Mathematics, a singularity is in general a point at which a given mathematical object is not defined or a point of an exceptional set where it fails to be

Singularity effect occurring at Max Q during launch of Apollo 11.
Singularity effect occurring at Max Q during launch of Apollo 11. In Aerospace engineering, max Q is the point of maximum Dynamic pressure, the point at which aerodynamic stress on a spacecraft in atmospheric flight is maximized

One view of this phenomenon is that it exhibits the effect of compressibility and the so-called "N-wave". In Thermodynamics and Fluid mechanics, compressibility is a measure of the relative volume change of a Fluid or Solid as a response The N-wave is the time variant pressure profile seen by a static observer as a sonic compression wave passes. The overall three-dimensional shock wave is in the form of a cone with its apex at the supersonic aircraft. This wave follows the aircraft. The pressure profile of the wave is composed of a leading compression component (the initial upward stroke of the "N"), followed by a pressure descent forming a rarefaction of the air (the downward diagonal of the "N"), followed by a return to the normal ambient pressure (the final upward stroke of the "N"). The rarefaction may be thought of as the "rebounding" of the compression due to inertial effects. [1]

Singularity effect seen in the BAKER shot of Operation Crossroads
Singularity effect seen in the BAKER shot of Operation Crossroads

These condensation clouds, also known as "shock-collars" or "shock eggs," are frequently seen during Space Shuttle launches around 25 to 33 seconds after launch when the vehicle is traveling at transonic speeds. Operation Crossroads was a series of Nuclear weapon tests conducted by the United States in the summer of 1946 NASA 's Space Shuttle, officially called the Space Transportation System ( STS) is the Spacecraft currently used by the United States These effects are also visible in archival footage of some nuclear tests. Nuclear weapons tests are experiments carried out to determine the effectiveness yield and explosive capability of Nuclear weapons Throughout the twentieth century most nations The condensation marks the approximate location of the shock wave.

Since heat does not leave the affected air mass, this change of pressure is adiabatic, with an associated change of temperature. This article covers adiabatic processes in Thermodynamics. For adiabatic processes in Quantum mechanics, see Adiabatic process (quantum mechanics In humid air, the drop in temperature in the most rarefied portion of the shock wave (close to the aircraft) can bring the air temperature below its dew point, at which moisture condenses to form a visible cloud of microscopic water droplets. The dew point (sometimes spelled dewpoint) is the Temperature to which a given parcel of Air must be cooled at constant Barometric pressure, Since the pressure effect of the wave is reduced by its expansion (the same pressure effect is spread over a larger radius), the vapor effect also has a limited radius. Such vapor can also be seen in low pressure regions during high–g subsonic maneuvers in humid conditions.

Prandtl-Glauert singularity effects can be readily observed on a humid day by successfully cracking a whip. The word whip describes two basic types of tools A long stick-like device usually slightly flexible with a small bit of leather or cord called a "popper" on the A visible cloud is produced at the point where the tip of the whip goes transonic.

Notes

  1. ^ It is important to recognize that the pressure profile rise-drop-rise is only figuratively described by an "N" and, indeed, it is better described as a "stylized-N" since the profile takes place within an ambient pressure context with pressure starting from, and returning to, the same ambient point afterward. Therefore, the "free-tips" on the end of the "N", relative to the center of the diagonal do not begin as low, nor end as high, as is implied by the normal shape of the letter N.

See also

External links

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