Aero dynamics
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Aero dynamics
Looking at those great photos of an F15 going round the Mach loop replete with wingtip vortices, it occurred to me that despite knowing why the vortices are generated, airflow over upper surface tends to move outwards airflow underneath tends to move inwards thus creating vortex, I realise that I don't know why the airflow behaves in this way. Why does the airflow move outwards on the upper surface and inward on the lower? Not too many formulae please I'm a dumb blonde (at weekends) .
You have it backwards:
When a wing generates aerodynamic lift the air on the top surface has lower pressure relative to the bottom surface. Air flows from below the wing and out around the tip to the top of the wing in a circular fashion. An emergent circulatory flow pattern named vortex is observed, featuring a low-pressure core.
Dog Tired
As PDR says, Both. And neither. In simple terms, the pressure differences below and above the wing bend the airflow downwards ie throw air towards the ground. Think of what happens when you turn a fan on, you get a cooling breeze ie it's throwing air into your face. Stand beneath a hovering helicopter, once again throwing air at the ground. An aircraft propeller, throwing air backwards.
