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
Discover more from Watts Up With That?
Subscribe to get the latest posts sent to your email.
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!
—…—
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.”