spoilers

Monstrobolaxa · Post 10 Dec 2005, 03:34

Hi Guys

Well my aerodynamics teacher the other day talked about perforated spoilers and mentioned that in some conditions they can have a higher Cd then non-perforated ones....well I asked at the end of the classe how they worked and he said he didn't know!

So he asked me to do a paper on the subject....and it would give me an extra point on my classification....

so those anyone know any links of sites that explain this situation? or have any concrete info on it?

Guest · Post 10 Dec 2005, 08:54

Shouldn't Race Car Aerodynamics by Simon McBeath help?

I'm not an aerodynamacist, but I'm thinking that with the perforations (assuming a serrated Gurney) that more air is going to be trapped at the stagnation point.

Or if you are talking about something like "dimples on the golf ball" it should be the same thing.

West

P.S. Tomba I dont think i can log in since I changed my email.

manchild · Post 10 Dec 2005, 14:35

To me perforations seams to have similar effect as counter flap - it makes more downfoce but also more drag than non-perforated wing.

West,
You must reactivate access to this site by confirming via link in e-mail that was automatically sent to your new address (I think so)

Scuderia_Russ · Post 10 Dec 2005, 14:39

Do you mean saw toothed rear wings? My understanding is that they produce a number of small vorticies instead of one big one.

Monstrobolaxa · Post 10 Dec 2005, 14:51

My question is about airplane wing spoilers....LOLOL

Well perforating them I've previously that in determined circumstances can reduce drag...it all has to do with the size of the holes and their inner surface!

In my opinion the holes (if small enough) will work as a venturi and speed up the flow, which in conjunction with the inner surface of the hole with raise slightly the surface drag of the flow going through the hole! Also drag is proporcional to the square of the speed...so if the flow in the hole speeds up depending on the way the hole is made it can increase the drag!

It also depends on the speed of the outer airflow!

manchild · Post 10 Dec 2005, 19:15

http://naca.larc.nasa.gov/digidoc/repor ... L51L10.PDF

Monstrobolaxa · Post 10 Dec 2005, 20:06

Thanks....but already have that one...and nothing spectacular! I really can't find info I can use!

guest · Post 11 Dec 2005, 13:57

I am not an aerodynamic specialist, but have heard a few things, maybe these can help:
At the surface of the wings at a thin layer the airspeed relative to the wing is zero, ruining the desired airflow and causing more drag.

-To remove this layer, Nasa has done investiogatons with an f16 having a special wing. On a small section of this wing were many thousand small holes, and inside the wing they were creaing depresion, drawing this layer.
-Using rough surface instead of flat polished, makes many small turbulences, breaking this layer. I think this is the reason why poilishing the whole intake ports makes volumetric efficiency worse.

DaveKillens · Post 11 Dec 2005, 17:14

That test F-16 with the thousands of microscopic holes was tested, but one serious flaw was that the slightest dirt or obstruction hampered the airflow through those holes. The are just too easy to plug up. Alll those holes had suction, so that the boundary layer was sucked out.
As far as the original holes in spoilers concept goes, I think its because all those holes caused a lot of vortices and eddy currents. Of course, that added tremendous drag.
One good example of such an application was the US Navy Douglas SBD Dauntless, with flaps/dive brakes with holes. It was designed to attack from directly over the target, going into a near vertical dive before releasing the bomb. During the attack/dive phase, it was desirable to keep airspeed as low as possible, hence the application of high drag spoilers.
http://www.warbirdalley.com/sbd.htm