Transonic (or transsonic) flow is air flowing around an object at a speed that generates regions of both subsonic and supersonic airflow around that object.
The issue of transonic speed (or transonic region) first appeared during World War II. Pilots found as they approached the sound barrier the airflow caused aircraft to become unsteady. Research has been done into weakening shock waves in transonic flight through the use of anti-shock bodies and supercritical airfoils. Transonic airspeeds see a rapid increase in drag from about Mach 0.8, and it is the fuel cost of the drag that typically limits the airspeed. Attempts to reduce wave drag can be seen on all high-speed aircraft. Most notable is the use of swept wings.
History
Discovering transonic airflow
In the 40s, Kelly Johnson became one of the first engineers to investigate the effect of compressibility on aircraft. However,wind tunnels did not have the capability to create wind speeds close to Mach 1 to test the effects of transonic speeds. Not long after, the term "transonic" was defined to mean "across the speed of sound" and was invented by NACA director Hugh Dryden and Theodore von Kármán of the California Institute of Technology. The slotted-wall transonic tunnel was designed by NASA and allowed researchers to test wings and different airfoils in transonic airflow to find the best wingtip shape for sonic speeds. Later on, Richard Whitcomb designed the first supercritical airfoil using similar principles. Aerodynamicists struggled during the earlier studies of transonic flow because the then-current theory implied that these disturbances– and thus drag– approached infinity as local Mach number approached 1, an obviously unrealistic result which could not be remedied using known methods. Many such 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 explosions are accompanied by supersonic flows and shock waves. Bow shocks formed in solar winds are a direct result of transonic winds from a star. It had been long thought that a bow shock was present around the heliosphere of the Solar System, but this was found not to be the case according to IBEX data published in 2012.
See also
- Anti-shock body
- Subsonic flows <!-- Change this link to subsonic flows if that article is created. As of 20th Dec 2006, the subsonic takes the reader to disambiguation page. -->
- Supersonic flows
- Hypersonic flows
- Supersonic expansion fans
References
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