Transonic


Transonic

Transonic is an aeronautics term referring to a range of velocities just below and above the speed of sound (about mach 0.8–1.2). It is defined as the range of speeds between the critical mach number, when some parts of the airflow over an aircraft become supersonic, and a higher speed, typically near Mach 1.2, when all of the airflow is supersonic. Between these speeds some of the airflow is supersonic, and some is not.

Most modern jet powered aircraft spend a considerable amount of time in the transonic state. This is particularly important due to an effect known as wave drag, which is prevalent in these speed ranges. Attempts to combat wave drag can be seen on all high-speed aircraft; most notable is the use of swept wings, but another common form is a wasp-waist fuselage as a side effect of the Whitcomb area rule.

Severe instability can occur at transonic speeds. Shock waves move through the air at the speed of sound. When an object such as an aircraft also moves at the speed of sound, these shock waves build up in front of it to form a single, very large shock wave. During transonic flight, the plane must pass through this large shock wave, as well as contending with the instability caused by air moving faster than sound over parts of the wing and slower in other parts. The difference in speed is due to Bernoulli's principle.

Transonic speeds can also occur at the tips of rotor blades of helicopters and aircraft. However, as this puts severe, unequal stresses on the rotor blade, it is avoided and may lead to dangerous accidents if it occurs. It is one of the limiting factors to the size of rotors, and also to the forward speeds of helicopters (as this speed is added to the forward-sweeping (leading) side of the rotor, thus possibly causing localized transonics).

Interesting facts

* At transonic speeds intense low-pressure areas form at various points around an aircraft. If conditions are right (i.e. high humidity) visible clouds will form in these low-pressure areas as shown in the illustration; these are called Prandtl-Glauert singularities. These clouds remain with the aircraft as it travels. It is not necessary for the aircraft as a whole to reach supersonic speeds for these clouds to form.

Transonic Flows in Astronomy and Astrophysics

In Astrophysics where ever there are evidences of shocks (standing, propagating or oscillating) theflow close by must be transonic as only supersonic flows form shocks. Interestingly all the black hole accretions are transonic (S.K. Chakrabarti, ApJ, 1996, v. 471, p. 237), many of the flows also have shocks very close to the black holes.

The outflows or jets from young stellar objects or disks around black holes can also be transonic since they start subsonically and at a far distance they are invariably supersonic. Supernovae explosion is accompanied by super sonic flows and shock waves. Bow shocks formed in solar winds around the earth is a direct result of transonic wind from the sun.

ee also

* Critical Mach number
* Speed of sound
* Sound barrier
* Prandtl-Glauert singularity
* Anti-shock body

Other Flow Regimes

* Subsonic flows
* Supersonic flows
* Hypersonic flows

References

Theory of transonic astrophysical flows: Sandip K. Chakrabarti, World Scientific Publishers , Singapore (1990)


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Look at other dictionaries:

  • transonic — [tran sän′ik] adj. [ TRAN(S) + SONIC] designating, of, or moving at a speed within the range of change from subsonic to supersonic speed …   English World dictionary

  • transonic — also transsonic adjective Etymology: trans + supersonic Date: 1945 1. being or relating to speeds near that of sound in air or about 741 miles (1185 kilometers) per hour at sea level and especially to speeds slightly below the speed of sound at… …   New Collegiate Dictionary

  • transonic — An aircraft flight at speed ranges in which the airflow over some parts is subsonic and in other places supersonic. The transonic speed region lies between 0.8 and 1.2 Mach. This is the region in which an aircraft transitions from subsonic speeds …   Aviation dictionary

  • transonic — artimas garso greičiui statusas T sritis Gynyba apibrėžtis Greitis, kai santykinis greitis kartais mažesnis už garso greitį, o kartais didesnis negu garso greitis. Taip atsitinka pereinant nuo mažesnio už garsą greičio į viršgarsinį greitį ir… …   NATO terminų aiškinamasis žodynas

  • transonic — Of or pertaining to the speed of a body in a surrounding fluid when the relative speed of the fluid is subsonic in some places and supersonic in others. This is encountered when passing from subsonic to supersonic speed and vice versa. See also… …   Military dictionary

  • transonic — /tran son ik/, adj. Chiefly Aeron. close to the speed of propagation of sound; moving at 700 780 mph (1127 1255 km/h) at sea level. Also, transsonic. [1940 45; TRANS + SONIC] * * * …   Universalium

  • transonic — adjective a) just below, or just above the speed of sound b) passing from subsonic to supersonic, or vice versa See Also: plasmason …   Wiktionary

  • transonic — In ultrasound, describes a region of a relatively unattenuating medium. A distinction should be made between a t. region and an acoustic echo. [trans + sonic] …   Medical dictionary

  • transonic — tran·son·ic || træn sÉ‘nɪk / sÉ’n adj. close to the speed of sound …   English contemporary dictionary

  • transonic — [tran sɒnɪk, trα:n ] (also trans sonic) adjective denoting or relating to speeds close to that of sound …   English new terms dictionary