Homemade Wind Tunnel?

[Sumner]

This question I guess would be for Dan Warner.  Would this tape be considered a vortex generator?  Thanx, Bob

I can find some info on the web about it, but can't find it.

its this stuff ya can get from aircraft spruce that looks like thick scotch tape

I've looked on their site and even called them with no luck.  They directed me to products they had designed to walk on a wing and not fall off.

I see where 3M has made it and it was even used on the hull of the boat that won the America's cup (name right?).  JackD probably has this stuff all over his boats below the water line so he doesn't get caught by the inspectors .

I can't find it on the 3M site.  It is also called riblet film.

If someone can find more info and a site that sells it please let me know.

c ya, Sum

[tomsmith]

http://www.wingsandwheels.com/page29.htm

Here is a site with an assortment of tapes.  Notice that on full size airliners just before the high point of the wing they sometimes have little metal blades a few inches long and an inch or so high set at alternating left/right angles.  These are the "real" vortex generators.  There are sites that sell these for private aircraft, but they look a little dangerous to bump up against, something like the inside of a food processor.  The tapes look a lot safer.

[Reverend Hedgash]

I was reading up on sailplane turbulators (thanks to piquing my interest by reading stuff posted here) and found this site:

http://www.sinhatech.com/auto.asp

The deturbulator is claimed to work by reducing the drag caused by the big void travelling behind a hatchback or 4wd type profile car. It does this by creating some turbulence at the top rear edge of the roof which breaks the connection between the air being dragged behind the car and that flowing over the roof. This means the air behind the car is pulled along behind the car acting as a kind of virtual tail and not spending valuable energy dragging and mixing in a big way the air travelling over the top of the car.

Renault or Citroen were  trialling versions for production vehicles last year with good results.

Obviously it is not perfect (It doesn't affect the turbulence caused by the sides or air coming from underneath) and a better solution is not to be landspeed racing a car with this boxy profile. It is a stop gap solution to an existing profile and not necessarily a method for designing a better lakester or bellytank.

Dirty Dave mentioned paint roughness.
To best maintain laminer flow at the front the smoother the surface the better. As the boundary layer thickens and flow separation occurs the surface roughness becomes less critical.

It makes sense that surface roughness could help slipperiness in the same way that the tapes do (or vortex generators) as all a tape is is a rough surface. What order of magnitude and what pattern of roughness is the big question.

If you have ever patted a shark you would know they are rough as all getout, not squeaky clean like a dolphin and it is one of nature's way of sliperriness (that has inspired Thorpe's swimsuit.)

When you get to this level of detail though there probably are far greater advances that could be made elsewhere on the vehicle for the same amount of research and effort.

If you are reaching for that last 1 mph for the record then it just might come in handy...

Rev. H+

[PJQ]

One of the Hyabussa riders tried disrupters at Speed Week 05. His thingos are shaped like miniature surfboard fins stuck around the faring (about 3cm long, sticking up about 4mm, only about 2mm thick). Not sure whether it worked.

The bike didn't run in 06, but will be back with a vengeance next year - now that Joe's Bussa came over and moved the bar up a notch.

Does the humble golf ball add any value to this conversation? Or does the dimpled skin idea apply to flight pattern rather than efficient pushing through air.

Regs,
PJQ
Velocity Science Laboratories

[Reverend Hedgash]

A lot of a golf ball's lift concerns that it is a spinning object with the top travelling backward to the direction of travel. This means the air over the ball is travelling faster than that under the ball and then there is lift and the ball stays in the air longer.

What the dimples do is increase the surface friction and so the air stays closer to the surface of the ball as it goes around the ball and is dragged behind it helping fill in the void behind the ball.

The reduction of the original pressure drag behind the ball outweighs the extra drag of increasing the surface friction of the ball therefore it performs better than a ball without the surface bumps.

But a ball shaped like an aerofoil and no dimples would go even better. Not good for putting however.

So the dimples are again an attempt to improve the drag due to a poor aero shape by spending less energy elsewhere, so yes it is similar Pete.

Nothing beats getting the shape right in the first place though.

Rev. H+

[Flaircraft]

One of the do-it-yourself science books I bought several years ago has a section on home wind tunnels.  One of the tunnel designs submitted used cigarettes to generate smoke; the cigarette was placed inside a holder, kind of like a fuse in a fusible link.  The holder had a tube on either end which allowed air to be passed through the holder. The "exhaust" side of the holder was sealed to the cigarette butt so that the air passing through the chamber was forced to go through the cigarette and into the tube.  The smoke coming out of the cigarette was routed into a manifold which had several outlets which pointed downstream in the wind tunnel.

The tunnel we have at home has been useful in our model airplane aerodynamic studies and it was fairly simple to build.  We took a model airplane prop and mounted it to a motor we scored out of a discarded vacuum cleaner, and used it to suck air through the tunnel.   We decided on suck-through instead of blow-through to minimize the swirl effects that occur when using a propeller to move air through a tunnel.  We also have flow straighteners (basically a plastic grate) at the rear of the tunnel, right in front of the prop, to help maintain a smooth flow through the tunnel.

[jimmy six]

If I see any "dimple tade" on a car in impounds which doesn't not allow streamlining ahead of the cowl you will probably asked to leave and watch from the end of the road for a year or 2...

You won't want the "label" which the use of it will cause if your car cannot be streamlined.

2006 Rulebook page 40, 4.CC..Definition of Streamlining..

Just to let you all know it's been arround for a long time, and I look in impounds...Good luck...J.D.

[jimmy six]

OPPS Dimple TAPE !!!!

[hawkwind]

One of the Hyabussa riders tried disrupters at Speed Week 05. His thingos are shaped like miniature surfboard fins stuck around the faring (about 3cm long, sticking up about 4mm, only about 2mm thick). Not sure whether it worked.

The bike didn't run in 06, but will be back with a vengeance next year - now that Joe's Bussa came over and moved the bar up a notch.

Does the humble golf ball add any value to this conversation? Or does the dimpled skin idea apply to flight pattern rather than efficient pushing through air.

Regs,
PJQ
Velocity Science Laboratories

That was my bike , made my own vortex generators , and used some zig-zag tape and dimple tape  ( purchased from wings and wheels in the USA ) unfortunatly  was not able to gather any data as the bike had ignition problems all week ,was hoping to do some coast down tests ,the basic principle is to energise the thin layer of stagnant air (boundry layer )and make it turbulent , which pushes back and delays boundry layer seperation ,which decreases form drag , the problem for amatures like myself is to know where to place such devices ,as they can create more drag, than they help in drag reduction, a wind tunnel and some good CFD programes would help to know where to locate these type of devices
Gary