Wake turbulence hitting the ground

twotwowoo

twotwowoo

New Member
Here's an interesting question for you guys:

Assuming zero wind conditions, what happens to wingtip vortices (wake turbulence) when they hit the ground? Logically, I would assume they would dissipate, considering that they are a form of induced drag and ground effect would cancel them out. There is nothing in the AIM or any of the pilot knowledge guides about this. Any thoughts?
 
Well....The parking lot I park at in Newark is directly against the airport and frequently arriving aircraft frequently pass right over. A minute later you hear the vortice, a swooshing ghostly sound....then it hits the ground, dust flies and then it's over.
 
twotwowoo said:
what happens to wingtip vortices (wake turbulence) when they hit the ground?
Click to expand...

When an airplane flies overhead, the downwash produced by the lifting wing could be measured on the ground if instruments of sufficient sensitivity were available....The final manifestation of the downwash produced by a lifting wing is a very small pressure rise over a very large area of the Earth. The net effect of this pressure rise integrated over the total affected area is a force applied to the surface of the Earth equal to the airplane's weight...The vortex model that we have used to describe the effects of downwash on a finite wing is based on inviscid flow....In reality, viscous effects in the air will eventually dissipate the wingtip vortices. However, the net downward momentum associated with these vortices does not change as a result of this viscous dissipation. No matter how large the viscosity, this downward momentum will eventually reach the ground, where it produces an aerodynamic force equal to the airplane's weight.
Mechanics of Flight, Warren Phillips, page 79.
​
 
Big whirls have little whirls
that feed on their velocity,

and little whirls have lesser whirls
and so on to viscosity.

--L.F. Richardson
 
Watched a 757 land over my head here one night, totally dead calm night... the plane flew over some 20 foot high maple trees on approach,about 15 seconds after it passed the trees started quite vigourously being tossed about for a few seconds, then calm, pretty much what you would expect?
 
I think they simply loose energy as they hit the ground/surface and die out within less than a minute or two.

If the winds are more or less calm in San Fran and you land behind a heavy on 28 left or right, you can sometimes see the wake hit the water just off the approach end. I've seen it churn up the water in two perpendicular lines and after a brief time the water calms down again. Pretty cool to see actually.
 
I went jogging in a park outside SAT with planes flying directly over at about 300'. You can hear the vorticies very clearly. I wonder what would happen if you were jogging and got hit by one.
 
Lee D said:
I think they simply loose energy as they hit the ground/surface and die out within less than a minute or two.

If the winds are more or less calm in San Fran and you land behind a heavy on 28 left or right, you can sometimes see the wake hit the water just off the approach end. I've seen it churn up the water in two perpendicular lines and after a brief time the water calms down again. Pretty cool to see actually.
Click to expand...

Whoops, I meant symetrical, not perpendicular.
 
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