DIY Wind tunnel to study Split Tips ?

Discussion in 'Hydrodynamics and Aerodynamics' started by Erwan, Dec 21, 2018.

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ErwanSenior Member

Hi Everybody,
The split tips is one option, among others which aims to reduce the induced drag of lifting surfaces.
You can find a lot of research by googlelizing these 2 keywords.

Unfortunatly any workpaper addressing this issue is based on fixed winglets or "feathers"
But according to how these feather tips work on a birds, variable bending and variable twist seems to be the way to go, and the reason why it it improves the induced drag.

I don't know to which extend it is possible to use OpenFOAM to achieve a model to study this arrangement, but I am afraid the learning curve is likely to be steeper than real world experience on the beach. That is why I bring to the forum the following question:

As I have no access to a wind tunnel I was wondering if it was not possible to create a box in plywood
which could be put on the beach when there is enought wind speed to mimics sailing condition's apparent wind velocity. (Conditions would be with the wind coming from the sea, on a flat beach with minimum waves).

The wing tips geometry is based on 3 staggered "feathers" which would hold in a 1m x 1 m area.
So each of them would be around 33 cm maximum chord and 1 meter span for the longest.

Each of these staggered wing-tips would be made like a "nano-windsurf rig" (1m span & 33 cm wishbone length, using a 5 mm diameter pultruded carbon rod tappered for the nano mast.

The idea is to settle the box at some height above the beach in order to minimize the impact of the big turbulences which might be bigger the lower you are from the beach.

In order to avoid a wind tunnel box as long as the rig height (6 meters for a Moth and 9 meters for an A-Cat) I would like to know if anybody has any idea on how to make a shorter box than the rig height
while being able to account the upper/lower airflow divergence*

*The upper side (low pressure side of a wing/ extrados) sees its air flow tilted by a tiny angle of a few degree at most , towards the center of the wing.
While the lower side (hight pressure side of the wing / intrados) sees the air flow tilted towards the wing tips.

So if I have not the full span to mimic the actual air flow on all the wing. I wonder how to address this issue before to start anything.

What seems appealing to me with this idea is :
1-The low cost of the experience, but time.
2-The possibility to use plexiglass in order to make movies of the flow around the tips
using fog and or telltales + others usefull devices I don't know yet.
3-The size of these 3 staggered winglets would more or less actual size for application on Moth & A-Cat
4-The weight of this top part of a rig would be much lighter than any other last meter of any classic rig (a 5 mm carbon rod in T 300, after tappering would be less than 30 g / meter).

Any idea or suggestion are welcome.

Merry Xmas and fair winds

Erwan

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Merry Christmas and Happy New Year! Experimental foil tips for the Wasp foiler:

3. Joined: May 2009
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Location: Cocoa, Florida

If you haven't seen this ,you might find it interesting:

Attached Files:

• Wingtip Feathers.pdf
File size:
106 KB
Views:
413
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ErwanSenior Member

Tkx, It is a patent. But I will focuse on how to mimic apparent wind conditions in a DIY windtunnel.

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DolfimanSenior Member

Hi Erwan,

Interesting but IMO very hazardous to have consistent results without the context of state of the art wind tests in a full equipped wind tunnel.
- The box itself should be rigid enough and not vibrating/oscillating in the wind.
- How to measure drag consistent difference which should range in few % from one test to another.

On the other hand wind tunnel specialized on wings may not necessary, cheaper experiences in atmospheric wind tunnel specialized for buildings and bridges may be sufficient >>> you can contact their experts to better define your experience, e.g. from CSTB :Les souffleries atmosphériques http://www.cstb.fr/fr/plateformes-essais/souffleries-atmospheriques/

Joyeux Noel,

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Doug HalseySenior Member

If you are only using the natural wind to create the flow over the model, of what use is the box? Wouldn't you be better off just setting the model on the beach?

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ErwanSenior Member

Yes you are perfectly right.
You prompt me to consider that an appropriate end plate could make the job, instead of a full box, and in addition, it would cheaper.
I d like to put it horizontal in order to make movies of the split tips at work.

As I d like to have the last 2 meters only, I just need to suss out a solution on how to reproduce the titling of the flow inboard for the low pressure side and ouboard for the high pressure one, equivalent of the full rig with only 2 meters span.