How do Vortex Generators work?

Vortex Generators

Courtesy: - wikimedia

Vortex generators is small device used to improve stability of the aircraft and delay its stall. But how do they do it?

Before going ahead lets take a look at basics of fluid mechanics.
To understand vortex generators it is necessary to know about boundary layers.

What is boundary layer?

Consider an air is moving over any aerofoil. (Aerofoil is simply cross section of an Aerodynamic shape). If we take a look at microscopic level, velocity of the air just above the surface of the aerofoil will be zero. This is because of viscous & frictional forces between air and aerofoil surface. So due to viscous and frictional forces velocity of air just above aerofoil surface will be zero. Due to this stationary layer air above this layer will slow Down again due to viscous force. This forms region above surface of the aerofoil with gradually increasing velocity of air. At far distance from the surface of the aerofoil there will be a point where velocity of the air will be equal to velocity of incoming air. So the region from surface of an aerofoil where velocity of air is zero to this point is known as boundary layer.

Need of Vortex Generators

Formation of boundary layer with high energy keeps air flow in contact with wing surface.
But at slow speed and higher angle of attack this air flow seperates from the wing surface and some times aircraft stalls.
Also some times airflow seperates from the wing before reaching to control unit such as ailerons. And pilot looses controls!
So to overcome such problems, Vortex Generators are used. As name suggests vortex generators forms vortex and energize the boundary layer.

How Vortex Generators work?

At slow speed and higher angle of attack airflow cannot remain attached with wing due to its low energy. So here comes vortex generators. Vortex generators forms vortices. Vortices are just small tornados. Actually vortex generators brings high energy air above boundary layer near the surface of wing by forming vortices & energize boundary layer. This keeps airflow attached with wing and reduce the possibilities of aircraft stalling.

Other use of vortex generators

Vortex generators are used under wing of Airbus A320 family aircraft to reduce noise generated by airflow over circular pressure equalisation vents for the fuel tanks. Lufthansa claims a noise reduction of up to 2 dB can thus be achieved.

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