When vortex are generated from the surface of wings just above the boundary layer, for a high lift co-efficient, they help to reduce drag and generate more lift whereas for low lift co-efficient, they generate more drag. I want to ask that how to differentiate between the point where this efficient wing will change to a non-efficient wing like what co-efficient will make a mid-point between efficient and not efficient wings. Please do answer it theoritically as by CFD analysis we may get the desired results but what would happen physically there?
Then perhaps your proposition doesn't exist, and there is no "point where this efficient wing will change to a non-efficient wing", unless you are talking about the stall point.....
DaveW wrote:Then perhaps your proposition doesn't exist, and there is no "point where this efficient wing will change to a non-efficient wing", unless you are talking about the stall point.....
I was talking about the stall point... I realized it's physical essence. Thank you, DaveW!
A vortex on the low pressure side of a wing will create a situation that allows the wing to work at a larger angle of attack (AoA) than without it. This increase in AoA creates an increase in maximum CL. While it does increase the maximum CL, it also does experience a fairly large drag increase.
What I mean by this is that if you require a certain amount of lift, it will generally be more efficient to go with a wing that has more surface area (lower wing loading) and a higher aspect ratio (a long and thin wing). However this introduces problems such as weight increases, stiffness issues and high speed drag characteristics.
It is not precisely the "stall point" of the wing where a vortex will make a wing more efficient. To get technical you have to introduce things like wing design. Wings don't stall all at once. They will stall at the point of highest pressure gradient first, the flow separates and starts to spread to other parts of the wing. Mounting pylons and objects ahead of a wing can create situations where part of a wing may be in a stall configuration while the rest of the wing is not. In this situation a vortex can help to keep that part of the wing working and on a whole make the wing more efficient, even at relatively low CL values.
As a general rule the point where a wing is stated to "stall" is a good point to use when working out if a vortex would be beneficial to increase CL.
P.s. Sorry it is really jumbled and probably doesn't make sense to many people. It is early, I am tired and didn't get enough sleep.
A wing has a number of vortices. But vortices in or adjacent the boundary layer, i.e. a turbulent boundary layer, can be useful in keeping the slipstream attached to the wing. These can function rather like roller bearings within the boundary shear layers, and/or between the boundary layer and the slipstream. Wing efficiency is binary between the attached and detached condition (stalled) so the turbulent boundary layer is marginally less efficient, it’s a major improvement over a stalled wing.
trinidefender, can you post an image of the wing where part of image is in stall configuration and the rest is not? I searched but relevant images won't show up
