A question about vortices 2

[Polypoker14]

Hi! I am starting to do research on aerodynamics of aircraft and I read that vortices are one of the main reasons for drag, and as vortices are caused by a sudden mix between 2 different pressures, if we managed to gradually introduce the higher pressure into the lower pressure via holes that gradually got more frequent so that at the end of the wing, the pressure would be similar, could we increase aircraft efficiency?

 

[LittleInch]

You might find that you lose quite a lot of lift....

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Compositepro]

The effect a vortex is similar to turbulence, which is just a bunch of micro-vortices. And it really is not the existence of the vortex that is absorbing energy, it is the continuous flow of air being accelerated into the vortex that is then left spinning in the wake.

It is similar to how a centrifugal pump creates a vortex with the impeller. If you close the outlet valve the pump consumes relatively little energy by spinning. When you open the valve, fluid with kinetic energy leaves the vortex, and entering fluid must be accelerated into the vortex (absorbing energy from the impeller).

 

[rb1957]

but then why to wing tip devices work ?

another day in paradise, or is paradise one day closer ?

 

[rb1957]

As I remember my aero (from Way more years ago than I care to remember !!??) lift is due to circulation around the airfoil.

And the wing tip vortex is a loss, so it can be improved (reduced). Thus we have many different wing tip devices "fences" to reduce the vortex with little impact on total lift.

They also have proposed circular wings, joining the wing tips together. This removes the wing tip but causes other losses and negative practical losses (I suspect it's a bit of a "disaster" when it comes to side slips and maybe gust response).

another day in paradise, or is paradise one day closer ?

 

[Compositepro]

I just saw a video of the newest 777 flying at an air show. No winglets. The wings taper to a very narrow tip and are swept back.

 

[rb1957]

yes, winglets were originally intended as cheap upgrade, to improve airplane efficiency. Then they started appearing on new clean sheet designs. Now Boeing are starting a clean sheet without them ... bet they'll get added some years from now.

another day in paradise, or is paradise one day closer ?

 

[3DDave]

The development of the vortex is inextricably tied to the production of lift with a wing of finite span. The wing is essentially shearing a width of air within the atmosphere and forcing that width down from within air that is not being forced down. The vortex is because of this difference. The vortex forms because of the energy put into the air to produce lift; want less vortex? Generate less lift.

The effect of winglets is to increase the apparent span by the length of the winglet without increasing the projected span. This is advantageous to passenger aircraft where gate spacing is a problem, but adds minor structural problems and some weight; it was seen as a cheap way to increase span but more as a fashion accessory as it gives aircraft owners an additional vertical area for decoration, much like tail fins did on 1950s cars.

There have been a number of collisions in ground handling that were made possible or made worse because of winglets striking or being struck by other aircraft when there was otherwise enough vertical separation for wing and tail surfaces to otherwise clear.

 

[WKTaylor]

PP14...

The subject You are engaged-in is not necessarily intuitive... drag all adds-up... differentially... throughout flight at various configurations and conditions... etc.

And never forget that drag elements due to propulsion [YES] has its own unique issues/characteristics... and can dramatically change aircraft performance.

Air vehicles NEVER fly solely at one design point... designs are often compromises with the devil [real world].

There are a few knowledge starting points You might find useful... as a foundation...

Fluid-Dynamic Lift: Practical Information on Aerodynamic and Hydrodynamic Lift (2-Ed) - S. F. Hoerner

Fluid Dynamic Drag: Practical Information on Aerodynamic Drag and Hydrodynamic Resistance - S. F. Hoerner

AGARD-CP-124 AGARD Conference Proceedings No 124 on Aerodynamic Drag

AGARD-AG-264 Aircraft Excrescence Drag

AGARD-R-786 Special Course on Skin Friction Drag Reduction

[RTO AGARDograph 300 … Flight Test Technique Series – [many volumes] AG-300-V**]

AFWAL-TR-84-203 Prediction of Aerodynamic Drag

Regards, Wil Taylor
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