F / A-18 aircraft
Su-57 at the MAKS-2015 air show
The Prandtl-Gloert effect is the condensation of atmospheric moisture behind an object moving at transonic speeds. Most often observed in aircraft . The effect is named after the German physicist Ludwig Prandtl and the English physicist Hermann Gloth .
There is a common misconception that the occurrence of a cloud due to the Prandtl-Gloert effect means that it is at this moment that the plane overcomes the “ sound barrier ”. In fact, the manifestation of this effect depends not only on the speed of the aircraft, but also on the relative humidity of the air . In conditions of normal or slightly high humidity, a cloud is formed only at speeds close to the speed of sound . In conditions of very high relative humidity, the effect can be observed at much lower speeds, for example, on the aerodynamic elements of cars during Formula One races in rainy weather.
Reasons to
The cause of the effect is that the aircraft flying at high speed creates an area of high air pressure ahead of itself and a low pressure area behind. After the flight of the plane, the area of reduced pressure begins to fill with ambient air. At the same time, due to the relatively high inertia of the air masses, first the entire low pressure area is filled with air from nearby areas adjacent to the low pressure area. This process is locally adiabatic , where the volume occupied by air increases and its temperature decreases. If the humidity is high enough, then the temperature may drop to such a value that will be below the dew point . Then the water vapor in the air condenses into tiny droplets that form a small cloud.
As the air pressure returns to normal, the temperature in it levels out and again becomes above the dew point, and the cloud quickly dissolves into the air. Usually his lifetime does not exceed seconds. Therefore, during the flight of the aircraft, it seems that the cloud follows it (due to the fact that the low pressure area is constantly formed behind the aircraft), and then disappears.
See also
- Sound barrier
- Condensation trail
Links
- Gallery of Prandtl-Gloert effect photos with links and other information.