Vortex Generators - How do they work
Would anyone out there like to have a shot at explaining to me EXACTLY how vortex generators work?
Yeah sure, they delay boundary layer separation (i think) and due to this, they give you an increase in MTOW, they redcuce stall speed and Vmca, blah blah blah........................ But how do they do what they do. I need an in-depth and logical explanation please. :bored: |
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Separation occurs when the boundary layer losses energy, basically it slows down and separates.
Vortex generators mix the less energetic air with more energetic air just above the boundary layer. |
Originally Posted by cessnaman172
(Post 2989210)
Yeah sure, they delay boundary layer separation (i think) and due to this, they give you an increase in MTOW, they redcuce stall speed and Vmca, blah blah blah........................
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At high angles of attack the boundry layer will become 'unstuck' and the aircraft will stall. If you can imagine a large curlover of air, departing the top wing surface such that the curlover causes airflow at the trailing edge to be reverse in direction to flight, along the top surface. The vortex generators, being proud of the surface, cause a similar but smaller curlover in a lateral sence. If you wind a bit of paper around a stick then pull the ends apart you get a coil of paper like the coil of a spring, this is what the vortex might look like if you could see it. The airflow of the vortex has the effect of reaching up and grabbing the departed air and returning it to the wing and thus re-establishing a boundry layer, even though it is a turbulant one. This allows the wing to continue to fly when otherwise it would have stalled. When you fit high lift devices to the leading edge, the the wing will still fly but be uncontrollerble because the reverse flow at the trailing edge is in the wrong direction for the alerons to work. Vortex generators are thus normally place ahead of the alerons in this case so that the alerons will still function in the correct sense even into the stall, thus making the aircraft safer to fly at low speeds.
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If you've ever opened up the stopper in a sink full of water and watched the water swirl down the drain, you know what a vortex is. Simply put, it is an energetic swirling mass of fluid. Vortices are quite common in aerodynamics. Probably the most well-known and significant of these are the trailing vortices that are seen coming off the tips of wings in flight. These vortices are not desirable because they create a type of drag known as induced drag, or that drag induced by a surface generating lift (like a wing). Aerodynamicists often spend considerable effort trying to reduce the adverse effects of such vortices. However, vortices very similar to trailing vortices can also be used to produce beneficial effects, and one of the methods used to create beneficial vortices is the vortex generator.
When an aircraft flies at high angles of attack, the airflow over the wing can become detached, or it stops following the shape of the wing. When this happens, the lift produced by the wing will suddenly and rapidly decrease, and the wing stalls. When the flow separates from the wing, it usually means the air is moving too slowly, or there isn't enough energy in the flow to keep it moving. Since vortices are energetic, they can be used to put energy back into the flow to keep it moving in the desired direction. This is what vortex generators are designed to do. Vortex generators are simply small rectangular plates that jut above the wing surface. They look like tiny little wings jutting up perpendicular to the wing itself. As air moves past them, vortices are created off the tips of the generators just like the trailing vortices mentioned earlier. These vortices interact with the rest of the air moving over the wing to speed it up and help reduce the possibility of separation. Vortex generators are typically used in the following applications:
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