PDA

View Full Version : vortex generator



gazz
12-04-2009, 10:48 PM
Has anyone fitted or know of one that would fit the Legnum? Would it even look any good!! Just curious to know if it had been done before.

bigoxo
12-04-2009, 11:22 PM
what do you mean by a vortex generator? do you mean the air intakes like the pipercross viper or the type used on aircraft to reduce airflow separation?

gazz
12-04-2009, 11:37 PM
like they fit to the roof on the evo's

bigoxo
13-04-2009, 09:50 AM
I suppose looks is is up to the individual, functionality probably couldn't be proven without a wind tunnel! Good luck tho, i'd like to see the result.

rees
13-04-2009, 03:24 PM
i know what hes on about , its been mentioned before , one of them miracle cures that increase bhp and feul economy , u see em on ebay

a proven gimmick that do naff all


dont bother with em

Roberto
13-04-2009, 03:40 PM
If you really want to:

http://www.k2motor.com/spl-vort7-abs.html

But would suggest it a cosmetic mod rather than anything else.

rees
13-04-2009, 03:52 PM
ah right i thought u meant the air intake thinng , ignore me lol

gazz
13-04-2009, 11:06 PM
Yes the funny spikey things that fit along the roof, cant make up my mind if they would look good or not. I'll look out for a universal kit thats local to me and see what I think.

Turbo_Steve
14-04-2009, 11:50 AM
Nah, not on a Leggie: that's just trying too hard to be an Evo!

Confused
14-04-2009, 12:12 PM
I seem to remember something vaguely about them being there to break up the air that flows along the top of the car, which aids with downforce when you've got a fairly large rear spoiler (something about ensuring the airflow carries on somewhat towards the spoiler, rather than following the lines of the car.

You might get away with it on a saloon with a large spoiler, but it'll be worthless on anything else - especially a Leggie with no rear spoiler after the spike doofer thingies!


Of course I could well be wrong - I just remember something about that when the Evo FQ-400 came out with them on the roof!

I-S
14-04-2009, 01:47 PM
Mitsubishi wrote an excellent white paper on the subject:

http://www.mitsubishi-motors.com/corporate/about_us/technology/review/e/pdf/2004/16E_03.pdf

From research I've done on them from other forums, etc, they can be effective at the back of the roof on a saloon, reducing flow separation down the rear window. However, on an estate you have too big of a discontinuity at the top of the tailgate, so you get flow separation regardless of whether you have vortex generators or not. Note that mitsubishi themselves did not fit vortex generators to the evo IX wagon, while the IX saloon came so equipped.

Also remember that vortex generators do themselves increase drag. It is their nature of reducing flow separation that causes a net reduction in drag. If you fit DIY vortex generators without doing CFD analysis and wind tunnel testing, chances are that you will not reduce flow separation, but rather you will increase the drag of the vehicle for no benefit.

If you want to improve aerodynamics simply, look into underbody smoothing as there's gains to be made there without the same level of analysis and testing required.

Ghost_2008
14-04-2009, 01:55 PM
This was taken from Wiki, but in short if fitted to the front of the roof of a leggie they may maintain a more constant flow of air accross the roof, therefore ensuring that you keep a constant down force.

I spoke with a friend of mine regarding drag racing, we kind of came to the conclusion that a leggie with the large flat roof would probably produce more down force than the salloon....... all theoretical of course........ but i wouldnt have thought that they would make any difference, if you buy an aftermarket set you would have to calculate the geometry of each "fin" to make the most of them..........

Vortex generators are likely to be found on the external surfaces of vehicles where flow separation is a potential problem because vortex generators delay flow separation. [3] On aircraft they are installed on the leading edge of a wing in order to maintain steady airflow over the control surfaces at the rear of the wing.[2] They are typically rectangular or triangular, tall enough to protrude above the boundary layer, and run in spanwise lines near the thickest part of the wing.[1] They can be seen on the wings and vertical tails of many airliners. Vortex generators are positioned in such a way that they have an angle of attack with respect to the local airflow.[1]

A vortex generator creates a tip vortex which draws energetic, rapidly-moving air from outside the slow-moving boundary layer into contact with the aircraft skin. The boundary layer normally thickens as it moves along the aircraft surface, reducing the effectiveness of trailing-edge control surfaces; vortex generators can be used to remedy this problem, among others, by re-energizing the boundary layer.[1][2]

Vortex generators delay flow separation and aerodynamic stalling; they improve the effectiveness of control surfaces[2] (e.g Embraer 170 and Symphony SA-160); and, for swept-wing transonic designs, they alleviate potential shock-stall problems (e.g. Harrier, Blackburn Buccaneer, Gloster Javelin).

Roberto
14-04-2009, 03:22 PM
I spoke with a friend of mine regarding drag racing, we kind of came to the conclusion that a leggie with the large flat roof would probably produce more down force than the salloon........


Is that not why Volvo ran 850 Estates in the BTCC?

Ghost_2008
14-04-2009, 04:55 PM
Possibly, the theory is sound, especially given the legnum's stance, as the back does seem to be that bit higher than the front...... there's also an arguement that the weight distribution is closer to 50/50 in the legnum due to the extra weight at the back.......... I'm sure someone with more experience can confirm......