Also, you needn't appeal to a heuristic argument to explain the existence of trailing vortices. Inviscid vortex dynamics requires that a vortex cannot simply end in free space, and so the bound vortex responsible for the lift NASA Aerodynamicist Craig Streett wrote: of the wing must go somewhere at the wing tip; this is the so-called Lighthill horseshoe Trailing vortices do in fact sink by their mutual vortex system, which also explains the cause interaction, but they also move together, until of induced drag. they become unstable and pinch off into connected rings - the so-called Crow instability. There are literally thousands of pictures and studies documenting this Finally, while the popular press calls behavior. Only when the tip vortices are in encounters under the generic term of ground effect, when they are interacting with "turbulence", they are classified formally in their below-ground images, do they travel flight sciences as "gust" encounters, to away from each other. distinguish from true atmospheric turbulence resulting from meteorological mechanisms. Atmospheric Turbulence By Tom Irvine Figure 1. Jet Streams Jet streams flow from west to east in the upper portion of the troposphere. They are caused by the temperature difference between the warm equator and cold poles. High pressure air from the warm tropics flows toward the low pressure at the cold poles, but the Coriolis force from the Earth's spin deflects these winds to the east so that they make an eastward circle around the globe. Introduction Jet Stream are numerous sources of atmospheric The main jet streams are located near the turbulence, including mountain waves, tropopause, the transition between the instabilities, thunderstorms, jet troposphere (where temperature decreases stream, as well as thermal updrafts and with altitude) and the stratosphere (where downdrafts. temperature increases with altitude). Clear Air Turbulence Jet streams are caused by a combination of the rotation about its axis and The turbulence may be clear air turbulence atmospheric heating. (CAT) if there are no clouds or other visible signs. This turbulence can cause "air The Jet Stream is formed as a result of pockets." An air pocket is a downward air the temperature gradient between the cold current that causes an aircraft to undergo a polar air mass and the warmer sub-tropical air sudden decrease in altitude. mass.
NASA Aerodynamicist Craig Streett wrote: Trailing vortices do in fact sink by their mutual interaction, but they also move together, until they become unstable and pinch off into connected rings - the so-called Crow instability. There are literally thousands of pictures and studies documenting this behavior. Only when the tip vortices are in ground effect, when they are interacting with their below-ground images, do they travel away from each other. Also, you needn't appeal to a heuristic argument to explain the existence of trailing vortices. Inviscid vortex dynamics requires that a vortex cannot simply end in free space, and so the bound vortex responsible for the lift of the wing must go somewhere at the wing tip; this is the so-called Lighthill horseshoe vortex system, which also explains the cause of induced drag. Finally, while the popular press calls encounters under the generic term of "turbulence", they are classified formally in flight sciences as "gust" encounters, to distinguish from true atmospheric turbulence resulting from meteorological mechanisms. Atmospheric Turbulence By Tom Irvine Figure 1. Jet Streams Jet streams flow from west to east in the upper portion of the troposphere. They are caused by the temperature difference between the warm equator and cold poles. High pressure air from the warm tropics flows toward the low pressure at the cold poles, but the Coriolis force from the Earth's spin deflects these winds to the east so that they make an eastward circle around the globe. Introduction are numerous sources of atmospheric turbulence, including mountain waves, instabilities, thunderstorms, jet stream, as well as thermal updrafts and downdrafts. Clear Air Turbulence The turbulence may be clear air turbulence (CAT) if there are no clouds or other visible signs. This turbulence can cause "air pockets." An air pocket is a downward air current that causes an aircraft to undergo a sudden decrease in altitude. Jet Stream The main jet streams are located near the tropopause, the transition between the troposphere (where temperature decreases with altitude) and the stratosphere (where temperature increases with altitude). Jet streams are caused by a combination of the rotation about its axis and atmospheric heating. The Jet Stream is formed as a result of the temperature gradient between the cold polar air mass and the warmer sub-tropical air mass.
September2011_NL.docx