Via the Wakey Wakey thread, I got wind of this photo (seen below the continue reading line) which is a real world effect of the model at left.
It seemed worthwhile to share for the sheer uniqueness of it. The turbulence caused by the turbines is a catalyst for cloud formation. See photo:
h/t to WUWT reader “Betapug”
UPDATE: In comments reader Mike G located the original photo as being from an offshore wind project by Aeolus called Horns Rev1. I’ve updated the caption and the photo as a result. Wikipedia has an entry with a map here
– Anthony
Don’t clouds trap heat way more effectively than CO2 ?
Stephen Salter, 2002:
“SPRAY TURBINES TO INCREASE RAIN BY ENHANCED
EVAPORATION FROM THE SEA”
http://www.mech.ed.ac.uk/research/wavepower/rain%20making/shs%20rain%20paper%20Feb.pdf
He wants to increase rain in arid regions by using a wind turbine and spray sea water into its wake.
Wow! What a picture!
Add this to the clouds made by ships and high altitude airplanes and you will find that the humanity is actually driving the earth into an ice age.
Contrail to popular belief…
So they are useful after all! They create clouds which cool us down and reduce HICC-UP. And, as a fortuitous by-product, generate meagre amounts of electricity.
Nice visualization of the turbulence created by these things. I fly regularly from an airport that has numerous turbines in the area and with the correct wind direction and descending below the top level I can feel the turbulence and it spoils my nice approach to the runway. It might even become dangerous for a pilot if he/she is not prepared for these effects.
Just got to love the way that the turbines are neatly arranged to fall in the wind shadow of the first row. Another day when “rated capacity” fails to materialise…..
Looks the same as the condensation cones from wing tip vortices from aircraft wings in fact exactly the same.
Wind turbines cause climate change ?? As if ….. !!!!!
Not that they’re a blight on the landscape or anything, but it’s OK though. If the albedo effects plunge us prematurely into the next ice age, I’m sure we can count on our elected politicians to help us muddle through it.
Do these reflect sunlight back, or intercept the outgoing?
So, – now more funding is really needed as this shows that more research is needed to establish “once and for all” whether clouds have negative or positive effects on Climate Change (CC). My plea to scientists is: “please form an orderly queue!”
I think that’s not a real photograph, rather a photo-shopped image.
Semi-relevant:
Here’s a NASA propaganda film from 1980 pushing the benefits of wind power. NASA started working on wind in 1973.
http://www.archive.org/details/those_magnificent_wind_machines
A few points:
1. NASA determined at that time that two blades were ideal, not three or more. Wonder why they changed to three?
2. It appears that the gov’t pushed the spread of cable TV across America to clear the way for wind power, because the blades created near-total interference with broadcast TV.
3. “We’ve found that the diesel generators used for backup have to be run at part-throttle when the wind turbine is producing, so we haven’t saved as much fuel as we thought.” Hmm. Seems that they still haven’t solved this one.
3. “The cost should drop to 5 cents per KWH.” That would be 13 cents after inflation today.
I can’t find a conclusive figure for real cost of wind power online, but a couple sources indicate that tax breaks amount to 23 cents, and the actual cost of operation and maintenance (not counting capital cost or the backup power) is 27 cents.
http://www.wind-watch.org/documents/true-cost-of-electricity-from-wind-is-always-underestimated-and-its-value-is-always-overestimated/
http://social.windenergyupdate.com/pr/new-report-explores-true-cost-wind-turbine-operations-maintenance
Wow is that photo real? Anyone know why the cloud trails are wider to the right? is it an optical illusion or something to do with wind direction? Inquiring minds pls
Wow, maybe Martha’s Vineyard is about to undergo a ‘sea change’ in its cloud patterns?
I have yet to get a handle on how a driven blade generates turbulence, my experience having been entirely on driving blades. All the turbines above are in the wake of the front row, probably reducing output and definitely putting more stress on the hubs and those long blades.
Neat, long rows may look tidy, but when the wind is just right, you lose efficiency. A pair of staggered placement grids would have been better, angled the way halftone screens are angled in color printing.
Interesting. So what albedo effect do the low clouds (assuming they are low clouds) have? Do they raise temps or lower them?
Very interesting photo. Where was it taken?
Wow. It also clearly shows that most of the windmills are in the turbulent wake of the front ones, so their already dismal efficiency is even worse.
Heh, I’ve been saying for years that the energy from a windmill is less than the energy taken out of the atmosphere, energy that is no longer available for those downwind. Efficiency losses mandate that the cure for such a tort is not available.
===================
That is an amazing photo. I have observed the same sort of effect trailing behind a fast boat with a complex mast like a Destroyer. Albeit to a much lesser degree.
And speaking of fresh snow, we awoke to an inch or so this morning. Latest accumulation I have ever seen.
Commentators on the previous “Wakey-wakey” thread seemed to have missed the obvious that this turbulence equates to noise. Wind turbines would be noisy even if the incoming airstream was laminar and all at the same velocity. Add in wind shear when velocity at the top of the blades is greater than at the bottom of the sweep and inflow turbulence either from natural changes in wind speed and direction or fixed structures such as trees, hills and buildings or other upwind turbines then the noise becomes much worse with a thumping quality that travels long distances and ruins sleep.
The wakey wakey tag is thus highly appropriate as that is what they do, wreck sleep patterns. As some other commentators have pointed out, much of this work was done by NASA in the 1980s and is conveniently ignored by today’s wind industry.
Wind turbines generate three things, subsidies, enriching the developers and pushing the poor into fuel poverty, noise, ruining the sleep and health of those unfortunate enough to live nearby and electricity, in small varying quantities that gives the grid operator endless headaches.
I share the concerns about what will happen to these giant symbols to political gullibility when the penny finally drops and the subsidies are axed. The developers will simply walk away, leaving them to desecrate our skylines for decades to come.
That is is clear evidence of anthropogenic warming by increasing the climate greenhouse effect by “trapping” long wave radiation.
OR
That is clear evidence of anthropogenic cooling by increasing earth’s albedo.
Calling climate modelers and experimentalists to rescue us from our plight!
Beautiful picture, but I would not like to live ‘down wind’ of these monstrosities. You would never see the sun.
OK I don’t like windmills which are for me, expensive 17th century technology in a new form.
Yeah! And they cause rotation of air. Fueling tornados! Sorry, couldn’t resist after yesterday tornado outbreak.
It wouldn’t surprise me at all if some of today’s climate scientists would suggest such connections given current standard in the climatic research community.
We saw that picture of the Horn’s Reef wind farm before but it was not greatly noted for it’s influence on cloud formation……
I speculate this is not a unique event for that site…..
Murray Grainger says:
April 28, 2011 at 4:18 am
I completely agree–now all they need to do is paint the turbine blades in fantastical colors and patterns so we can enjoy them like the toy pinwheels we all had as children.
The original for this appears to be at http://ict-aeolus.eu/about.html
The home page of the Aeolus website says:
“Aeolus is an European research project funded by the European Commission under the IST framework programme 7 for Information and Communication Technology, ICT.”
The site describes the conditions present at the time of the photo:
“Horns Rev 1 wake effects. Photographer Christian Steiness. The above photograph shows the turbulence field behind the Horns Rev 1 offshore wind turbines. Unique meteorological conditions on 12 February 2008 at 1300 hours resulted in the wind turbines creating condensation (i.e. clouds) of the very humid air, thus making it possible to see the turbulence pattern behind the wind turbines. “
Polistra wrote-
“1. NASA determined at that time that two blades were ideal, not three or more. Wonder why they changed to three?”
I heard that with three blades, you have asymmetry, so the wind mill will always start turning even in low wind conditions. With 2 or 4, the symmetry can stall rotation in low wind speed conditions.
That’s the explanation I read.
-Jay
Whether these clouds trap or reflect heat is complicated and depends on where they are as well as the prevailing weather conditions at the time.
To whoever asked about the switch to three blades instead of two as NASA recommended, in most wind conditions three blades transmit more consistent stress to their mounts, making the total turbine more reliable. Two blade designs are preferable in some wind conditions, but three are preferable in most.
I will be very surprised if anyone ever gets a good model on the effects of clouds on the heat transfer problem. Years ago, I was flying over western Kansas when I noticed that the clouds formed a reasonably precise checkerboard. I finally noticed that the farmland below had been plowed on a checkerboard pattern. I suppose that the farmers had some kind of pattern where alternate sections were used on alternate years with the remaining sections allowed to rest for a year, but the result was a set of clouds that exactly indicated the plowed/not plowed surface beneath them. It would be very difficult to convince me that enough data could be gathered to input to a model so that something like this could be accounted for in computations. To suggest that models could effectively utilize that vast amount of data would only serve to reduce (if possible) my estimation of your credibility.
Jay
3 also gives more uniform moment of inertia about the vertical axis – less jerk when changing orientation.
Anyone check out the poll from the page with the original graphic of the wind turbine aerodynamic modeling??
http://www.ssdl.uvic.ca/index.php/component/poll/16-do-energy-costs-need-to-rise-to-avoid-climate-change
Looks like drastically higher energy prices are the solution to climate change!!
Are we sure ths pic is real? I saved it thinking it would make a great desktop background but enlarged the windmills look kinda “funny”
#
Dermot O’Logical says:
April 28, 2011 at 4:22 am
Just got to love the way that the turbines are neatly arranged to fall in the wind shadow of the first row. Another day when “rated capacity” fails to materialise…..
###
That was my first thought too. Must just be a coincidence, but maybe not. I have seen a company who likes to put up Press Release generating solar panels up on their campuses. At one the panels are tilted towards the east, at another they are tilted towards the west. Not only did they get it wrong, but they were not even consistent in their wrongness which means they were built just for show. But they sure are photogenic and look all cool and s**t over the parking lots they now cover.
Chris H wrote-
“Commentators on the previous “Wakey-wakey” thread seemed to have missed the obvious that this turbulence equates to noise. Wind turbines would be noisy even if the incoming airstream was laminar and all at the same velocity.”
So where do I go to hear this noise? I have been in the wake of a windmill and not noticed it, though I wasn’t listening or trying to discern the source of noises around me.
After reading previous reports of the noise from windmills I have driven to near the base of a windmill only to have the noise of the machine drowned out by the noise of the birds in the bushes nearby. I returned later and could hear the machine: it sounded similar to my neighbor’s air conditioner, but not nearly as loud as the AC. It was more the same level of noise as the tires of the traffic on the interstate a half mile away over the hill. The generator sounded like a bearing was failing.
I’m guessing I was probably too close to hear noise of turbulence. (about 300 ft from the base of the windmill)
Where in the wake, at ground level, do you have to be to hear the noise of the turbulence, and where do you have to be to not hear it for a comparison?
Regarding the drying effects, in Iowa and the corn belt there are at least some observers have noticed fewer high temperatures in the summer and fewer droughts. This they attribute to the effects of the increased density of planting corn shielding the ground from the sun. In the last 20 years the average density has gone from mid-20’s thousand plants per acre to mid-30’s thousand plants per acre. That increased crop density should also protect the ground from the turbulence of a windmill.
yes it is real seen the same effect with our local “Nowhere Oregon” wind farm.
Vestas has been revealed as the true owner. BTW. That gives me even less confidence.
Being an old Fire Dog (Wildland, Aerial) i keep wonering what these thing would do to a fast moving wind driven fire? Especially the big ones….
This is the only picture I’ve seen of a wind farm with the contrails. My conclusion is: it’s a rare phenomenon.
Andy G55 says: April 28, 2011 at 4:06 am
quote
Don’t clouds trap heat way more effectively than CO2 ?
unquote
No. Not low level cloud. Low level clouds reflect sunlight (albedo around 60 to 70 compared with calm ocean albedo of effectively zero). Those who doubt that low level clouds are a cooling phenomenon should book an open-ended holiday on the north-east coast of England and wait for the haar. This is a drift of low level fog/stratus/stratocumulus cloud from the sea onto the land. Sit on the beach on a summer’s day under the haar and you will learn about albedo. Bring a fur coat.
JF
Everyone is asking whether clouds trap heat or cool the surface. I asked it too, once. One analysis we received in a recent post was that it all depends on yata, yata, yata. In other words, no one really knows the overall result of clouds on temperature. Sometimes warmer and sometimes cooler. The when and where of each does not seem to be very predictable.
This is an example of turbine cooling primarily causing human-induced climate change.
This could mean that current IPCC model predictions for the next century are wrong, and there will be cooling in the North Sea.
ewj. 300ft is too close to really get the thumping swooshing noise that is so annoying.
All turbines produce this noise pattern but in some it is worse than others. The problem is that the industry doesn’t seem to have a clue what causes it or how to prevent it. Factors that seem to be important are turbine size, blade length in relation to tower height (long blades and short towers), blade design, hilly terrain, high wind shear, multiple turbines in lines and too close, ridgeline arrays.
The lack of studies of the human effects rather than abstract calculations is disgraceful.
That is an amazing photograph. One could certainly claim that it proves that extracting energy from the wind, results in a Temperature drop. I’ve observed the same auto cloud production around cars on the freeway; often when going over the Grapevine to SoCal. With the cars moving through the saturated air, just the Bernoulli pressure drop is enough to cause condensation.
And since these turbo-clouds are low level we know from climatism 101 that they cool the earth; unlike those high noctilucent clouds that warm the earth because they are so high, and don’t block much sunlight. Well we do know that the noctis do block some sunlight, because that is why they light up, since they are in daylight.
How did this nonsense gain traction, that those white puffy clouds heat the earth surface, by “reflecting” sunlight off their sides down to the earth.
Draw a picture of the sun earth illumination system. If you are in daylight, and lets say not within 20 minutes of sunrise or sunset, then the sun is likely of the order of five degrees above the horizon or more.
And you see a nice white puffy cloud above you raining down excess sunlight on you to warm you up.
Now disappear that very cloud; and what happens ?
Well the sunlight that was raining down on you from that cloud, now goes whizzing right on by you and slams full force and unscattered (largely) into the ground, just a little bit closer to the sunset horizon.
So you now get all of it on the surface, whereas, with the cloud there, the sunlight scattered off the cloud side, goes about half up, and half down, since the scattering is essentially isotropic, so about half of the sunlight that hits that cloud can hit the earth, and the other half must exit to space. Remember it is solar spectrum sunlight; and not cloud sourced LWIR thermal radiation.
The very fact that clouds increase the earth albedo; by ANY amount, is proof positive, that they ALWAYS reduce the amount of solar energy that strikes the earth surface, to be (mostly) stored in the deep oceans.
So can we please stop saying that extra sunlight off the side of white puffy (ok, cumulus) clouds, increases the Temperature.
Now that’s one weird negative feedback.
Increased temperatures causes greenies to panic and start blaming enhanced CO2
To replace the CO2, greenies start planting wind turbines.
Wind turbines cause an increase in low level clouds which start cooling the earth.
polistra: I remember reading somewhere that one blade was even better. The article had a picture of a single bladed turbine with a small counterweight on the other side.
Though from a purely economics standpoint, a zero bladed turbine would be even more efficient.
“The developers will simply walk away, leaving them to desecrate our skylines for decades to come.”
Dynamite is your friend.
jorgekafkazar: I suspect you need air that’s pretty close to the saturation point. On the other hand, I’ve read that oceans are the new prefered places for putting wind farms.
“”””” jorgekafkazar says:
April 28, 2011 at 8:35 am
This is the only picture I’ve seen of a wind farm with the contrails. My conclusion is: it’s a rare phenomenon. “””””
Well those particular turbines aren’t going to go anywhere any time soon, so I imagine that they are going to sit there in that ocean proximity nearly saturated air , and when the wind blows, I imagine that you could see this on a regular basis.
Let me put it this way; I believe I could make more money running sightseeing tourists out to watch this phenomenon; than I could running whale watching trips out to the same place.
The wind farm, in California’s Pacheco Pass, has the same phenomenon, because of the close proximity to the San Luis Reservois.
If you go out in Monterey Bay in the summertime, you will often encounter low level fog offshore; and as you drive through it, you will notice one other thing; it is virtually always blowing underneath that fog. The wind over the surface carries off the water vapor, leaving an H2O deficit, and normal evaporation proceeds apace, putting a lot more water vapor into the air. I can’t say that I have ever encountered offshore fog without it being windy; and it has always been in summertime; which is not to say we don’t get offshore fog at other times, I’ve just never been out in it at other times.
That picture is genuine. There’s a detailed investigation into efficiency losses due to wake vortices effecting downstream turbines here:
http://www.dongenergy.com/SiteCollectionDocuments/NEW%20Corporate/PDF/Engineering/40.pdf
Is this a belated revenge (for 1066) by the Danes (that’s where these windmills are located), on the English (that’s the direction these clouds will be going), then?
Thanks for the Wikipedia Horns Rev link. It has a revealing bit about how well thought out the project was:
Regardless of sea conditions? I’m sure Willis or someone will correct me, but AFAIK when sea conditions are bad there’s a lot of fast-moving winds. So when sea conditions are bad, they can lower workers out of a helicopter, on a long-enough cable to avoid the wind turbine blades, with strong winds, dangling said worker next to the (rotating?) turbine blades, until depositing them on the small platform.
I hope they have good health and death benefits, with long-term disability and rehabilitation provisions.
Horns Rev 2 is somewhat different.
For only 91 wind turbines, they need a fully-equipped dormitory, 24 rooms, with TV, internet, and a gym. That must do wonders for the economic viability of the wind farm.
Gee, they have all that free wind energy. Maybe they could add a greenhouse and/or pursue oceanic aquaculture, do some fishing, and declare it a self-sufficient colony. You know the Greens won’t be happy until Evil Mankind is driven from the land it so willfully despoils. This could be a good start!
Peter Dunford says:
April 28, 2011 at 4:35 am
Do these reflect sunlight back, or intercept the outgoing?
Yes.
“”””” Chris H says:
April 28, 2011 at 9:54 am
ewj. 300ft is too close to really get the thumping swooshing noise that is so annoying.
All turbines produce this noise pattern but in some it is worse than others. The problem is that the industry doesn’t seem to have a clue what causes it or how to prevent it. Factors that seem to be important are turbine size, blade length in relation to tower height (long blades and short towers), blade design, hilly terrain, high wind shear, multiple turbines in lines and too close, ridgeline arrays.
The lack of studies of the human effects rather than abstract calculations is disgraceful. “””””
Well all they need to do is to talk to some bass fishermen; or even fly fishermen, who routinely use electric trolling motors to get around relatively quietly in fishy waters.
The guy just got through testing out his electric while the boat was sitting on the trailer, and everything was hunky dory, just a quiet whrirr from those small blades.
But he no sooner get out to his fishing spot, which is always on the other side of the lake from the launch ramp so he has to go seventy MPH to get there; and he drops his electric into the water to move silently in that shallow fishy spot, and the damn electric has developed a wobble something fierce, and is shaking sometimes quite violently; yet it was fine on the trailer.
Maybe he had it down while running and hit a branch and bent the motor shaft. Trouble is that it still was nice and quiet when he got the boat back on the trailer ashore.
Well it’s the water equivalent of wind shear. The blade at the bottom is in deeper higher pressure water, and can get a better bite on the water, with less slippage, so it creates a greater thrust. But the blade at the top of the rotation, is in very shallow water, sometimes just inches from the surface, and the water can more easily flow over the top of or around the blade; it is easier to move out of the way, than to put up with that pesky blade.
As a result, the propeller blades experience a cyclic thrust variation that is synchronized to the rotation rate, and it is significant enough to shake the whole assembly quite violently.
Same goes for wind turbines, the blade passing over the tower, is in stronger winds, developing higher torque, and also higher axial thrust, but when the blade is closer to the ground, in lower speed wind, the left and the drag drop per the square of the wind speed, so the blade undergoes both an axial, and a circumferential oscillation that is synchronized to the rotation rate, and keeps flexing the blade, until it fails from fatigue stress.
If you build the tower taller, for a given propeller diameter, the wind speed differential drops, so it gets less shaky; but now the taller tower, has to endure more bending stresses, so the tower has to be made much stronger, so that it doesn’t fail; because the tower too experiences the cyclic axial thrusts that each propeller blade exerts, as it rotates from top to bottom; and because of the blade axial flexibility, the three propeller tip thrust do not simply average out. Each blade tip, can only talk to its two companions after discussing the matter with the tower at the hub of the rotor.
So the solution is to simply stop the blades from rotating, or perhaps go back to a vertical turbine, which is a lot less efficient, but not so noisy.
Chris H wrote:
“ewj. 300ft is too close to really get the thumping swooshing noise that is so annoying.”
I think I acknowledged as much when I wrote the question. When I did my previous observation I was not looking for that effect, and was not located to observe it. When I have been near windmills previously I have not noticed the effect, but I was not looking and was not in the vicinity long enough to notice. So my question remains as before, where should I be to observe the phenomenon at ground level (since I do not have access to very tall ladders and cannot carry them in my small car)?
Presumably downwind but how far downwind should I be?
Roy says:
Wow. It also clearly shows that most of the windmills are in the turbulent wake of the front ones, so their already dismal efficiency is even worse.
Does this also mean more stress on the mechanical components of those further back?
This sort of effect is quite common.
You can see it in airplanes: take off on a clear morning and you can see clouds
form over the tops of the wings. You can see static waves become visible as
clouds in front of the jet engines.
You can see it in cars: look at a carburetor in a running car, or behind a
Gurney lip on a car that is moving
You can see it with firearms: watch a .76 cal Brown Bess fire on a cool morning,
or a .58 cal Hawken.
You can see it in the mountains in the right conditions. Sit on the summit and
watch clouds form from your fingertips. A variant of this is St. Elmo’s Fire.
http://cdn-www.airliners.net/aviation-photos/photos/5/0/1/1091105.jpg
I seem to recall this image being discussed here back when it first appeared. It may have been in a comment thread rather than a post. Though the photo caption indicates the phenomenon is the result of unique conditions, I seem to recall coming across several reports that suggested that while it is not common neither is it that infrequent.
The image is also interesting in light of this comment from the Wakey Wakey thread
Bill McCarter says:
April 26, 2011 at 8:43 pm
I was on the periphery of a study of this at the Boundary Layer wind tunnel at UWO in 1977. The results were that wind turbines should not be spaced closer downwind from another turbine at less than 28 diameters of the turbine size. Turbines in a line perpendicular to the prevailing winds, no problem, in a matrix, big problem.
It’s hard to say what the spacing is between turbines from one image, but it seems like they’re not even in the ballpark for 28 diameters at this installation.
Offshore wind power. I may have a …mini-scoop.
I blogged the Telegraph article, mentioned by James Delingpole, about a risk that whales get disoriented and stranded because of offshore turbines. Soon there’s a blog comment that the article is removed, replaced by a message that the scientists says they were misunderstood.
I didn’t answer the comment, but the traffic log says it was from the board room of Vattenfall, Sweden’s largest energy company. According to an article they have the largest plans ever to build offshore wind power in Britain. Was this a coincidence, or was it greed behind the removal of information from researchers and media? Only the suspicion that the latter is correct is …scary. “Mini-Russia style”?
Btw, I oppose conspiracy theories (but we know there are interests in the society, of course also when it comes to politically driven large state subsidized projects).
The thumping noise is merely the pressure variation as a blade passes. This is the same in a small airplane where a large part of the noise in the cockpit is from the prop blades passing the windshield. It is common nowadays to have active noise canceling in your headphones which generates anti phase pressure variations to reduce this noise greatly.
So there we were just turning on to crosswind at 500 feet after takeoff with the active noise canceling off when my wife reached up and turned the ANC on. I was looking to the inside of the left turn and didn’t see this. She was impressed by my immediate push to lower the nose thinking we’d had an engine failure. She tells me now before she turns it on.
Also around 20 years ago we built some equipment for a RAAF test project which involved flying the aircraft at about 100 feet AGL over a sensitive altimeter on the ground. The pressure increase from the aircraft (Pilatus PC9)passing overhead was equivalent to 1-2 feet of altitude quite repeatably.
It just so happens that I have a short video clip of Meridian Energy’s wind turbine, in Wellington New Zealand, that I took especially to demonstrate the noise. I would offer it to Anthoney to put here for everyone to hear, except that when I took it I forgot that my editing software doesn’t allow me to rotate video, only still shots, so the wind turbine appear horizontal. If you would like to hear the whine, the thump anf the apparent griding noises from a 250 kW turbine just let me know where to send to clip (20 MB so I’ll have to zip it).
A Wing tip device can reduce drag, diameter,noise and improve efficiency, at least according to Wikipedia.
Wonder why they are not seen?
Jantar says:
“I have a short video clip of Meridian Energy’s wind turbine, in Wellington New Zealand, that I took especially to demonstrate the noise.”
How far away from the turbine were you? I’d be interested to know how much noise there would be in the dead of night at say half a kilometre away. The power company should compensate anybody living within that distance, i.e. hundreds of thousands of dollars for each house involved. They can just factor that into their original costings.
Keith Minto
April 29, 2011 at 12:56 am
Wing tip devices (winglets) are on just about every modern sailplane. They aren’t going to help a wind turbine all that much. The rule of thumb seems to be that the height of the winglet is equivalent to an increase in span of about half that much. The winglet doesn’t increase the bending moment at the wing root by all that much , unlike the span increase which does.
How about counter rotating the blades of different windmills. this might recapture some of the turbulence.
jaymam: “I’d be interested to know how much noise there would be in the dead of night at say half a kilometre away”
I’m not involved in your discussion (so I may misunderstand something), but I’ve got a little knowledge from what I’ve read. Dr Nina Pierpont [1] says wind turbines may harm human health as far as 2 miles (about 3 kilometers), and one problem is also the low frequent infrasound. In France the took the decision to ban turbines within 1500 meters from any house where people lives [2].
[1] http://www.windturbinesyndrome.com
[2] http://www.windaction.org/news/2218
(I have actually a blog (in Swedish) with…
…these post has relevant info (with English video(s)) on harm to health:
http://klimathot-gameover.blogspot.com/2009/08/studie-om-vindkraft-och-halsa.html
http://klimathot-gameover.blogspot.com/2009/08/lite-kamp-mot-vindkraftidiotin.html
…and these post share experience (with English video(s)) on harm to health:
http://klimathot-gameover.blogspot.com/2010/10/wisconsinbor-om-vindkraftspark.html
http://klimathot-gameover.blogspot.com/2010/07/berattar-om-erfarenheter-av-vindkraft.html
http://klimathot-gameover.blogspot.com/2009/09/renewable-misery-ett-reportage-om.html )
Hope it can be useful…
I can’t specifically address the trade-off’s of winglet tips on (electric-generation) windmills, but they do appear to be a logical way to add “effective length” to a turbine’s rotor diameter.
Problems: The winglets increase frontal area (drag) and tip weight. Compared to the “front air flow” of an airplane or – more accurately – a sailplane’s wing, the centrifugal force of the spinning windmilll blade adds tremenddous tip loads because of that extra tip weight. Worse, the winglet is (by definition) at right angles to the blade. Thus, the bending force of the winglet’s weight – plus the aero force of the winglet’s “lift” back against the airflow rushing outward – is not only outwards from the rotor, but will be trying “bend-off” the winglet from the rotor blade – right where the winglet and blade are already most highly stressed. A sailplane – not facing any centrifugal force bending the winglet off – is less likely to break off the wing tip.
The aero-specialists who do rotor designs may have found that winglet-rotor tip breakage (at that rotor tip/winglet root joint) causes too much problems to be worth the extra lift from the winglet.
Counter-rotating props are exactly what they are trying to avoid. But the wind-turbine people are trying to exactly opposite what the airplane propeller engineers are achieving – so their opposition to counter-rotating props is expected. A propeller designer is trying force as much energy as possible into the (relatively static) air coming into his prop as his prop advances into the air at a very high rate of speed.
Airplane = 150 – 450 knots, air speed essentially zero, propeller very small (3 meter max) spinning very fast. Any rotating energy “left” in the air after it leaves the first prop can theoretically be used by the second prop spinning in the opposite direction. Note that only ONE airplane of all the tens of thousand designs built really is successful at counter-rotating props – the Russia Tu long-range bomber. All others in every nation have had severe bearing and engine failures.
A windmill has winds coming in between 10 and 36 knots, 100 meter diameter props turning only a few rpm. The aero flow across the prop lifting surface is very, very different. Any “left over” wind energy after the blade passes any single finite element of the air flow can’t be regained because it has already lost most of the energy it can give up. A second blade hitting that stagnant air stalls out – as you can see from the first picture.
Classically, I was taught you needed ten blade diameters behind the first turbine to recover the air stream for the next turbine – which appears to be about the distance in the RV photo. Haven’t seen 28 blade diameters before. Note that this by itself means that “neighborhood” windmill ranches can’t be used – first guy to make a windmill – using his neighbor’s subsidy tax money to save his own electric bill! – prevents his neighbor’s around him from building windmills to save money on THEIR electric bills!
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Haven’t read anybody’s question about the major differences between the old-style “farmer’s” multi-blade closely-spaced water pumps and today’s three-bladed electric generators. Difference is in the loads. The water pumping windmills – universally given up as soon as electric power was available to each farm! – are used to lift a heavy iron pump rod and water column “up” about 6 inches on each stroke. That sudden heavy load ( a rod could be lifting itself and the water column 200 ft to 500 feet deep) is applied as soon as the gear is engaged, so the water pump windmill needs tremendous static thrust, but low high speed thrust.
An electric-generator windmill needs to turn very fast against a very, very low torque when starting. In the generator (when starting the windmill) there is no current. With no current flowing, there is no counter-electromotive force (emf) is created in the stator, and that counter emf can’t be present until the loads are turned on when the switch is shut. So, with no starting torque to oppose, high speed blades with a large rotor are best. Little short squatty blades right next to each are not useless, just not effective.
My memory of ‘winglets’ is that they reduced wing tip vortex turbulence on heavy commercial aircraft, a good example is given by ‘clipe’ above….. http://cdn-www.airliners.net/aviation-photos/photos/5/0/1/1091105.jpg . That turbulence represents wasted energy.
I recall that light aircraft landing were flipped over by the rotating air currents, so the winglets were installed to prevent this happening and, of course as money is always involved, reduce aircraft spacing at landing and take off. The efficiency to me at least, seemed a secondary benefit.
I agree, I cannot see any benefit for turbine blades
1. I’ve no idea why the world obsesses over wind-power and very little attention is given to solar dishes equipped with sterling engines or thermoelectric generators (let alone Laser-ICF). Boggles the mind, I guess wind power is the popular trendy mainstream crap.
2. I’m amazed how many of you have no idea how increased albedo affects mean temperature. Come on guys this is basic high-school stuff. It reflects solar radiation for the same reason people in the middle-east prefer to wear white. If you can’t even figure that out then I suggest you drop by high-school and apologize to your teachers for falling asleep in class and wasting everyone’s time.
Excuse me while I cut my d!@& off and ensure I don’t subject offspring to this idiotic species.
“click the link to see image in the same size.”