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Three dimensional flow around Airfoil

 Three dimensional flow around Airfoil

When an aircraft is in flight, pressure is not only distributed in chord wise direction but also in span wise direction. Due to span wise distribution of pressure wingtip vortices are created. In atmospheric flight it is the tendency of fluid to move from high pressure area to low pressure area. The same scenario happens when an aircraft is in levelled flight.




Pressure of air is lower than atmospheric pressure at upper surface of the wing and higher than atmospheric pressure at the lower surface of the wing. Beyond the wing tips the pressure is normal. This causes the span wise flow of air away from the fuselage on lower surface and an inward flow towards fuselage on upper surface. Now the airflow is on both chord wise and span wise direction. Both meet at trailing edge of the wing, which imparts a twisting motion to the air and series of vortices are formed on the trailing edge. These are known as trailing edge vortices.



As the aircraft propels forward, at the wingtips the pressure gradient causes the air to flow upwards and large concentrated vortices are formed. These are called wing tip vortices. These vortices move in counter-rotating direction and become weaker as they move towards centre line of the aircraft.

The net effect of these vortices deflects the relative airflow downwards behind the trailing edge and within the wingspan which is known as induced downwash. In reality the amount of downwash is determined by the size of vortex, if the vortex is larger the greater the downwash.

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