Wing aero

[flyboy2160]

presumably he was not speaking (in aviation) of tip vortices ?

It was many years ago, so my memory isn't exact, but I think he was creating a mid-wing vortex with a leading edge snag to stabilize the airflow departure on the outer wing panel.

[flyboy2160]

Just wanted to chime in to say that this thread is excellent, and that I look forward to more, more, more....Anyway. Thanks to all who are contributing to this discussion and teaching me. Carry on!

I agree. I wish we had mostly this type of discussion and not any of the fanboi stuff.

[SAEED]

From Wikipedia:

Helmholtz’s three theorems are as follows:

Helmholtz’s first theorem: The strength of a vortex filament is constant along its length.

Helmholtz’s second theorem: A vortex filament cannot end in a fluid; it must extend to the boundaries of the fluid or form a closed path.

Helmholtz’s third theorem: In the absence of rotational external forces, a fluid that is initially irrotational remains irrotational.

Helmholtz’s theorems apply to inviscid flows. In observations of vortices in real fluids the strength of the vortices always decays gradually due to the dissipative effect of viscous forces.

Alternative expressions of the three theorems are as follows:

1. The strength of a vortex tube does not vary with time.

2. Fluid elements lying on a vortex line at some instant continue to lie on that vortex line. More simply, vortex lines move with the fluid. Also vortex lines and tubes must appear as a closed loop, extend to infinity or start/end at solid boundaries.

3. Fluid elements initially free of vorticity remain free of vorticity.

[Kiril Varbanov]

I'd like to drop a few words about vortices direction: for example, F1-practically speaking, the two strong formations coming out of the diffuser's lateral channels are counter-rotating. The downforce produced over there, by the diffuser, correlates with the rake (ride height) where this is related to the strength of those vortices. Generally, the airflow over the diffuser is of great interest, as combined with proper gurney flaps design helps increasing the downforce to some good levels.
The gurney flap size cannot be increased indefinitely, however, as this will cause pressure increase due to vortex burst or stall, hence the use of the perforated gurney flaps - merely to create and keep those vortices strong. In fact, this is area where teams are often having different shapes and gaps of this wickerbill to align with the track specifics.

[shelly]

presumably he was not speaking (in aviation) of tip vortices ?

It was many years ago, so my memory isn't exact, but I think he was creating a mid-wing vortex with a leading edge snag to stabilize the airflow departure on the outer wing panel.

here is a good example of snag on the leading edge: f138 font wing pylons



(posted by forza on the f138 thread)
The change in section creates a vortex that is useful downstream (I think it interacts with the front turning vanes under the nose)

[Tommy Cookers]

presumably he was not speaking (in aviation) of tip vortices ?

It was many years ago, so my memory isn't exact, but I think he was creating a mid-wing vortex with a leading edge snag to stabilize the airflow departure on the outer wing panel.

50s fighters Mig etc often had part-span leading edge-straddling 'fences' for this reason
the modern LEX feature is related to the modern long noses ?
which will themselves shed vortices at high AoA, preventing weapon aiming (as in the F-4)
unless designed as a chisel nose with related LEXs as in the (trendsetting) F-5
fins/vertical stabilisers seem from the 30s to have often used the 'LEX/LERX' configuration, for higher useable AoA

tip vortices can all be seen as helping the attached flow on the outer wing (ie boosting the useable AoA) ? (but the price is high)
lower aspect ratios have bigger vortices but stand higher AoA
straight (untapered) wings likewise relative to tapered wings
in many (not all) situations the accompanying tip vortices are for that reason the pilot's friend IMO

the (elliptical) front wing of the March 711 ? at Monza would have a fraction of modern DF, and a fraction of a fraction of the drag
the DF was too pitch sensitive, ...... but the tip vortices were small

[timbo]

here is a good example of snag on the leading edge: f138 font wing pylons

[pitcure removed]

(posted by forza on the f138 thread)
The change in section creates a vortex that is useful downstream (I think it interacts with the front turning vanes under the nose)

In this case it is as much a design feature as it is a crutch to get around regulations.

[shelly]

This picture from beginning of 2009, with DDD, before EBD, shows the same arched shape we still see on every fw, onlt this time applied to the diffuser footplate. The idea is the same: to have the vortex roll aroud the outer edge, run under the footplate surface guided by the arch shape.
Helmoltz 2nd theorem probably gives us some ideas about the usage of vortices as "virtual walls" or virtual sideskirts
(Interesting to see that it has not been widely used since then, because of exhaust usage probably - only ferrari last year had something similar in the zone, but it merged with a full width diffuser at the end)

[Pierce89]

I think most here underestimate the amount of DF that comes from these various vortices. In Racecar Engineering, Simon Mcbeth removed the bargeboards(main bargeboards and smaller ones under the nose) from the '07 Honda and TOTAL DF dropped by 40%. Now some of that loss comes from the bargeboards functioning as flow control devices, but the vast majority of the DF loss comes from the loss of the bargebord vortices. Also, a large portion of front wing DF and diffuser DF comes from vortices underneath the outer corners of each device. LMP's also generate a large portion of their front DF from VG's in the front diffuser

[Pup]

Probably something to learn watching this. If not, well, who cares - still an amazing thing...

[youtube]http://www.youtube.com/watch?v=aM0JMoGABgk[/youtube]

[flyboy2160]

presumably he was not speaking (in aviation) of tip vortices ?

It was many years ago, so my memory isn't exact, but I think he was creating a mid-wing vortex with a leading edge snag to stabilize the airflow departure on the outer wing panel.

here is a good example of snag on the leading edge: f138 font wing pylons

http://imgur.com/WjYUPfC.jpg

(posted by forza on the f138 thread)
The change in section creates a vortex that is useful downstream (I think it interacts with the front turning vanes under the nose)

Sorry, but this is an aero-geek version of the" You call that a knife?" scene in Crocodile Dundee: you call those wussy little things snags? This is a snag

[flyboy2160]

..
This picture from beginning of 2009, with DDD, before EBD, shows the same arched shape we still see on every fw...

Shelly, to which exact surface are you referring????

[wesley123]

The inverted gutter you see in between the diffuser and wheels.

[shelly]

On this picture of fw35 posted by stefan the two arches for the inner and outer fw endplate vortices are visible.
The multi-element, endplate-less fw design is closely related to housing and feeding (via the slots) the inner vortex that goes up with the flap, where the corner edge between flap and endplate was.

[shelly]

@timbo, flyboy - in the ferrari picture what i was pointing at (calling it snag for lack of a better word) is the change of section in the pylons above the "ferrari world" tag