Passive augmentation from the world of biomimicry

[rotornuts]

Well, in my search for a way to provide functionality to a wing over a wider range of AoA's without a great deal of drag penalty I came across this little nugget.

http://www.appliedfluids.com/UUST01.pdf

Seems naval researchers have determined what the tubercles(lumps on the lead edge)on a humpback whales flippers are for and the results are impressive. The lumps at the leading edge of the flippers serve to concentrate flow in the valleys at high AoA's and shed vorticies up to the apex of the lumps generating significant lift with minor drag penalties. At lower AoA's there is no penalty at all and the flipper behaves as it would without them.

It's easy to see how this transitions to the world of wings so I cut a set for my 2 cylinder Vawt but I extended them all the way back to the trailing edge which is now also zigzag shaped and agian I have no quantifiable data but my impression is that of a   decrease in weather vaning at startup, increased rpm and higher torque(finger friction test).

I'm going crazy that I don't have the resourse right now to scale this up and attach it to an alt. but soon I hope.

I'm down a camera again so no pics but I'll doo some drawingss of the new comfiguration later.

Thought some of you may be interested.

Mike

[rotornuts]

I failed to also mention the researchers noted a respectable reduction of induced drag over the same wing without tubercles.

It's all in the pdf. This would also work well on Hawt's

Enjoy

Mike

[drdongle]

I believe that I recently read an article on large turbine manufactures employing this technique, they apparently got it from the aviation people who are using it on small planes.

[Ungrounded Lightning Rod]

I'd heard about it but wasn't sure if it would work for compressible air or only incompressable water.  Nice to hear it works for air, too.

Now how can I add this to a sailboat's sail?  Also the rudder, keel, and maybe the hull...

[rotornuts]

I think your thinking about vortex generators Dr.D. Very similar in what they do but the vortex generators do so at much more expense in terms of drag when they're doing their thing(Augmenting lift and delaying stall at high AoA's). Also vortex generators do not reduce induced drag like the tubercles do.

Mike

[windstuffnow]

  Hey, you didn't hurt the whale stealing his bumps did you?  Next time I'm out and I see a slow whale... I'll know who to blame! Seriously though, what did you make your bumps out of?  Sounds interesting, is there a pattern that works the best or simply random?

 

[electrondady1]

  those numbers are very interesting.but its curious that only humpbacks  have evolved these features

[electrondady1]

  those numbers are very interesting.but its curious that only humpbacks  have evolved these features

[rotornuts]

Good day Ed. What I did was a make$#|+ adaptation of the tubercles. I took a 2 1/2" diameter foam flotation thingie, commonly refered to as a noodle and I hope my kids don't wonder what happened to it, and I shaved a 1/4" thick strip off of it which made it around 1 1/4" wide. I had already cut a zigzag pattern on the trailing edge of my new two cylinder model(back to two) so there where four points on each trailing edge. Each point got a strip of the semi-circular foam from the trailing edge to the leading edge(around the front to the zero point of the cord line at which point the strip is blended into the leding edge in a circular fashion. This in effect mimics the wavy leading edge over the full rotation of the blade.

I have no idea what the best configuration is but I would like to build a two cylinder with the tubercles biult in and double the amount of waves for the same proportion. Unlike the tubercles on the model described in the pdf I would like to continue the wave to the trailing edge instead of the aerodynamic center but they will reduce in height and width as they travel towards the trailing edge blending in with the wing. I'll also continue to incorporate a zigzig trailing edge because I think it helps when the wing is showing it's top to the wind and as it passes across the back of the unit.

I'll attempt a keyboard drawing  (>

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Something like that.

[rotornuts]

P.S. No whales where hurt in the making of this post.

Also I'm making some assumptions here but I believe part of the effect is the production of vorticies that travel up the sides of the wave to the apex where they hunker down and produce lift and delay stall in a similar fashion to vortex generators, this is why I'm assuming that the effect can be exploited even after the leading edge has fallen out of the incident wind.

Mike

[rotornuts]

Actually it makes sense that humpbacks have developed these given thier enourmous mass. They require a high lift system to move there large mass in tight circles. Many other whales and fish have a much smaller mass and many have a low aspect ratio flipper which  performs better over a wide range of angles but doesn't have as favorable a L/D ratio. I think other aquatic mammals have developed other adaptations that have their own unique features such as a hammerhead shark, I mean where'd that come from.

I just really dig on the bio mimicry stuff. First a maple seed now a whale. I wonder if cows have any unique aerodynamic features(other than flatulence).

Mike

[drdongle]

Interesting, when can you post some pictures?

[electrondady1]

i beleave cows to have a very low tsr. but if they give you a lift, it can be a real drag!   your in a tough position, with out an accurate monioring system in place, its difficult to measure improvements . runing different configurations simultaniously (same wind conditions) and compareing rpm is about the only route you can go.

[wooferhound]

I tried using some cows for props last year

The problem was getting them mounted onto the Hub

and the tower need to be really strong

Sorry ,  no pictures, I did'nt have my camera that day . . .

[ghurd]

Are you milking out every last drop of power?

G-

[rotornuts]

Here's what the current version looks like.





My apologies for the gaudy colors.

I have a theory on the zigzag trailing edge but it's very hard to explain. It does different things at different points in the rotation.

The yellow is the tubercles and if I use this for a scaled up test unit I'd like to try and blend it all together nicer. Unlike the whale flipper my tubercles extend to the trailing edge so I don't know if I can really call them tubercles but I believe the effect is the same.

Some day I will build a 2'x4' version of one of these things for real testing but till then I'll continue to play around and make changes based on visual obsevations. I figure if I can see a difference then it must be good. Trying to optimise visually is useless but so are these small models as far as collecting performance data.

Anyhow, the above modifications have made the two blader perform like the three blader but I'm seeing higher rpm's from the two blader as you would expect(or I would hope).

Mike

[phil b]

Interesting reading on effects of leading edge roughness and vortex generators. There's enough info here to build a set. I'm thinking it may help get a few more watts in low wind conditions.

http://www.wind.nrel.gov/OSU_data/reports/7x10/L417_7x10.pdf

[DanG]

I've been admiring Enercon blades for awhile - some are very low speed (17 RPM) and gearbox-free designs that get up to 370 feet diameter. I thought they borrowed many aspects, esp the root area, from great whales. None of the images I surfed off the web have details high enough to see leading edge clearly but a few hint of tubercles. Some show hints of perpendicular grooving after the leading edge though.

Water is 800 thicker than air so I don't think they need to be massive, the open-ocean racing sailboats use 3M films that mimic shark skin to create micro-eddies that reduce friction, Also Speedo (http://tinyurl.com/7jcex) uses braille-like dots above a smooth surface simiarly. I think this could better manage turbulence behind the blades middle and outer 1/3rd..

I am slowly working up a low RPM blade design (1.5m) for a small HV DC motor conversion (12v gives 10rpm) from cedar laminates that will now include tubercles on the root areas - probably the inner 25% with smaller ones added to the next 10% of blade length - THANKS for posting the article!

I also found this article abstract here --> http://tinyurl.com/ex2v5

__Hydrodynamic design of the humpback whale flipper:__

The humpback whale (Megaptera novaeangliae) is reported to use its elongate pectoral flippers during swimming maneuvers. The morphology of the flipper from a 9.02-m whale was evaluated with regard to this hydrodynamic function. The flipper had a wing-like, high aspect ratio planform. Rounded tubercles were regularly interspersed along the flipper's leading edge. The flipper was cut into 71 2.5-cm cross-sections and photographed. Except for sections near the distal tip, flipper sections were symmetrical with no camber. Flipper sections had a blunt, rounded leading edge and a highly tapered trailing edge. Placement of the maximum thickness placement for each cross-section varied from 49% of chord at the tip to 19% at mid-span. Section thickness ratio averaged 0.23 with a range of 0.20-0.28. The humpback whale flipper had a cross-sectional design typical of manufactured aerodynamic foils for lift generation. The morphology and placement of leading edge tubercles suggest that they function as enhanced lift devices to control flow over the flipper and maintain lift at high angles of attack. The morphology of the humpback whale flipper suggests that it is adapted for high maneuverability associated with the whale's unique feeding behavior...