OT: perforated spoilers

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?

I wouldn't say that this was OT.

Does this not fall into the same kind of category as the CDW wing being proposed for F1? All to do with the turbulence created "in the hole". I am intrigued.

Rob.

Here you go, found this with very little googling.
I think these people know what they are talking about:

http://naca.larc.nasa.gov/digidoc/report/rm/10/NACA-RM-L51L10.PDF

Rob.

Actually it's about airplane wings....that's why I called it a OT!

Thank you for the link...but I've already been there and still can't find enough info!

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!

Is this going along the theme of Golf ball indentations,????? I know that someone used to make stick on plastic sheets with built in indentations for improving airflow.
Ian :) :)

I've very tempted to be flippant, mostly because I find it hard to take any question seriously from someone who chooses that as a user name.... but I won't be.... this time ;)

Not my field, but perhaps a series of small perforations of the correct size could allow just enough flow to produce tiny vorticies as the flow accelerates through the hole. These vorticies might then stick to the low pressure face promoting better adhesion of the flow and allow higher attack angles before the flow separates. Sort of like an alternative to using a multi element spoiler.

:offtopic:

it never ceases to amaze me how many students seem to do there research here on 10/10,

it strikes me its a bit like asking the audence on millionare, but without giving any of the answers first! ;)

Perforated spoiler is the question. So this should be what your after:
http://naca.larc.nasa.gov/reports/1941/naca-wr-l-445/

Perforated spoiler is the question. So this should be what your after:
http://naca.larc.nasa.gov/reports/1941/naca-wr-l-445/
I think that's the 'report' that goes with the research document that I linked to.

If you read through the naca/nasa document, it shows the effect of the perforations on drag, and therefore shows what you are looking for.

Rob.

I haven't had the time to read the NACA paper, but perforations in wing sections are intended to break up the boundary layer on the low pressure side and so reduce drag with no loss to lift or downforce (depending on application!) I doubt they are/were used to create turbulence or vortices for any other reason (for example to improve stall charateristics) as there are simpler and more predictable ways of achieving that.

Many years ago either the Oxford or the Cambridge boat had used this idea on the bow of the 8s boat to make it more 'slippery' - and it worked really well! But as the bow of a boat has a constant angle of attack to the water (in plan view) it only had to be made to work for this one angle, unlike a moveable wing on a car, in which case the angle of attack may be changed to give a desired level of downforce, or an aircraft wing which changes angle of attack because of the attitude of the aircraft (e.g. in a climb, in level flight and in a dive but also when the control surfaces are operated which also affect the angle of attack - extending flaps being one example).

The beneficial effect of the perforations almost certainly limited to angle of attack, size of holes and location of them on the wing surface and so I imagine it would be an enormous task to determine how and when to use them in a real world situation without having your own wind tunnel.

the most successful aeroplane wing results feature literally thousands of miniscule holes and an engine driven partial vacuum inside the wing . No commercially viable way of mass producing the array of holes was developed, although laser is mooted as a possibility.