Why Do Wind Turbines Have Three Blades?
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- čas přidán 5. 09. 2024
- There is a lot more to this subject than I have covered in this video, this is just the basics. I have used the Wind Turbine Handbook as my primary reference material, it covers pretty much everything you need to know about wind turbines. If you are studying this subject academically I highly recommend it. You buy it on amazon here: www.amazon.com/...
Follow Real Engineering on facebook at:
/ realengineering1
My Instagram: / brianjamesmcmanus
Thank you to / kristianpont
For allowing me to use his sound record of wind turbines
Stock footage sourced from videoblocks.com
Once again thanks to Bensound.com for the amazing royalty free music. This time I used Bensound - New Dawn
References
[1] Page 340 Wind Energy Handbook - Tony Burton
I plan to remake this video at some point. It's a really shallow explanation. I simply did not have the skill and experience to make a longer video when this was released. I could crank this video out in a single day now. The subject definitely deserves a more in-depth explanation.
Cool, would be really interesting if you did. Perhaps a few consideration on offshore vs. onshore could be included as well as a look at underwater turbines. just suggestions of course. cheers and keep up the good work!
This explanation is good. It's not misleading in any aspect. Some details are left away but mainly it's a cost, structure and noise issue.
also look into single blade turbines...
Efficiency is low and bearing loads are high.
But maybe for small WEAs they make sense.
Go for that univerlag.uni-goettingen.de/handle/3/isbn-978-3-941875-75-3 and here into the appendix.
Please do, your videos are usually so much better. This video feels like it amounts to "3 is just better".
The generic cost graph didn't even hint at the effect of blade count and the video basically ignored the engineering concerns. (like Robb Stark's comments below on boundary layer related wind speed/stress balancing making even blade counts problematic).
It would also be nice to hear something on VAWTS.
hey, engineering student of renewable energies here, the centrifugal force is not a major reason why the turbines usually have 3 instead of 2 blades. It is due to the fact that in different heights you have different wind speeds and having an even number of blades gives you periodic stress on the system, when the upper blade encouters the highest wind speeds the lower blade is receiving relatively slow winds additional to passing in front of the tower which disturbs additionally. this periodic torque stress will wear down the machine pretty quickly, thus we use 3. plus your notion about the the wrenches is entirely wrong, doubling the blades wont double the torque, adding more blades will decrease the speed needed to extract the energy from the wind. unbelievable you didn't caught that contradiction, those principal are mutually exclusive. be a good man of science and remake the video instead of just putting a half-arsed remark in the notes about it being just the "basics". It's not that you left out additional information it's that you are factually wrong about your explaination. your channel looks pretty promising if you are able to take constructive critizism seriously. pm me if you want some references or advice , cheers
Why 3 blade turbine doesn't generate periodic force? Would you explain that a little?
sure basically with any even number of blades 2, 4 ....etc you have the blades arranged opposite of each other this is a bad setting as exactly as one blade is at the 12 o'clock position and experiences the highest wind speed and thereby the highest force the blade exactly opposite of it expierences the lowest winds and thereby force so putting torque on the machine with a really long lever. research "Growian" a german 2 bladed prototype that had first cracks after 6 hours into it's testing. if you built it even worse you can have this periodic swing coincide with the tower swinging it up and loosening the foundation bit by bit .(research bouncing betty for a very visible showcase of what resonance can do to structures) that's why you generally choose Primenumbers in engineering to avoid resonace(yeah i know 2 is technically a prime but i think you get what i mean) two blades counter the torque of the top one with those two being at higher levels(and wind speeds) and away from the tower in a 3 blade setting. i hope that helps Dan
Oh! Gotcha, I really helps. Thanks a lot Robb!
your welcome
good comment, i clicked the video waiting to see some kind of fluid dynamics explanation to why 3 wings would be more efficient to harvest energy, and the only thing i got was bad analogies and cost analysis... i would like the video to be remade as well :)
quite shallow explaination why not 4 blades. did not explain why the additional power is small, you just stated it. but thats the important part no?
I thought it was pretty shallow too... Why not shorten the 2 blades so they exert less torque --> less speed on top of saving money on material? Adding a third blade just to slow down the angular speed sounds fucky
Yep, sure a fourth blade costs 33% more, but if it's output is more than 33% it makes it worth it. There is really no reasoning for dismissing 4 blades so quickly.
Less torque = less power generated. Take a computer fan and blow into it. It's 7 blades and is spinning more times per second than a wind turbine. Quieter too. But it's not going to power your city.
The guy in this video doesn't seem to have a lot of knowledge about the technical part of windpower... Well yes, they cost some more to produce a fourth blade, but when we are talking about the whole project, then the fourt or fifth blades additional price increase is just some few percent....
THE MAIN REASON WHY WE USE 3 BLADES IS: There is a aerodynamical phenomena which is reason and it is someway hard to explain, but I'll try.. If you would have let's say 6 blades, then the wind speed would decrease significantly after the turbine. So imagine what would happen if the air behind the propellers stood still. Yes, the pressure in front of the turbine would also be higher, so the wind would "go around" the turbine. Because it would be almost the same thing as an unidentified physical obstacle would stay straight out in the wind. SO you want to get the wind to go through the turbine as fast as possible, but still take as much kinetic energy as you can from it. So there is this perfect ratio AKA Betz's law (en.wikipedia.org/wiki/Betz%27s_law) which says you can take maximun 59% of the energy from the wind, today we're at about 40-45% in the best cases... Then there is also the question, why three blades? Why not two? Or one? That's a different question... :D
Thank you for clearing that up, I really found the video explanation rather meager. By the way, I've seen a two-blade wind turbine somewhere, so there's probably a lot more going on behind the question "how many blades should a wind-turbine have?".
Ok, here's some real info for you - note I live in one of the world's largest wind turbine producing cities in China and do consultancy engineering for a few of the companies associated.
A one bladed WT is actually the most efficient, this is due to the air having time to recover by the time the next sweep comes around, having done some aircraft wing turbulence stories you may be able to visualize that. Problem for one blade is balance and harmonics, but that's another story.
2 blade is still more efficient than 3 for exactly the same reason, But in the real world, 2 blades are also hard to balance and align exactly opposing each other and a big harmonic problem when they "shade" - shading is when the lower blade sweeps past the tower where there is no air flow. The loss of pressure when shading makes the blade flick forwards as the wind pressure on the blade stops momentarily.
So simply put, one more blade, 3, is the minimal suitable for these factors. They are less disturbed by balance and shading issues which also helps to control harmonics.
Note that 4 would suffer shading issues like 2 does, so 5 would be the next choice, and note that many car radiator cooling fans have 5 so they can mass produce thousands with larger tolerances.
Well this is a better explanation than the damn video
I got that part of your explanation thanks, but I have got another one for you: blades as they are produced are long and thin, what would happen if you would make them shorter and more wide?
Ummmm .... Balance IS the story..
Also, I would think 3 blades provides MORE TORQUE... usable work, vs. velocity factor. I should think 4 may be even better, but I would wory of the air flow recovery factor. And, with 4 blades, the units probably have to be spaced even farther apart with great study of optimal placement based on prevailing winds being most important along with ability to anchor the beasies in stable ground.
That's a good answer. Also take a look at Robb Stark's answer above. Both of you are saying the same - it's the balance problem (related to the top blade receiving more wind). Seems that zero-blades rotor would totally eliminate vibrations :)
This is a very good explanation. Thanks.
Great video. Looking forward to the next!
+Wendoverproductions It's gonna be a good one ;)
Hey it's Wendover
@@RealEngineering you will?
Knew this schmuck would advertise his channel on growing ones.
@@colin-campbell both make really good videos
I passed one of these blades on the highway once. It took a long time to pass it. These things are so huge; when you are right next to it, it is unbelievable.
Dad once got to go up one and he still has the photos framed, it looks like he's atop a small skyscraper
@@cumguzzler8537 He went inside up the ladder, or outside. There is no way I would climb up an outside ladder. Even with a harness. No. Way. lol.
@@VidarrKerr inside ladder, the bigger ones almost always have integrated inside ladders
I like your channel a lot, but this video misses the spot way too far. I have the strong impression sure you just read the english wikipedia page, which, for whatever reason, does not cover the root of the problem in comparsion to other wikipedia languages and masses of other articles on the web about the topic.
Do you remember how three-phase electricity works and why it's magic? If the load is identical on all phases the fourth wire has zero current the other three equal out completely.
The same principle applies to a three-blade turbine similarly: There is zero unbalance and much less vibration. The forces on the central axis are always straight and therefore three-blade turbines last longer both in the gearing as well as in the tower construction, are less noisy and have a smaller tendency to soar into big fatal movements like in the crash you show in the video (they're not fully resistant either as you video shows :-) )
PS: Initial construction cost-wise a two-blade design seems to be the real sweet spot and if you research a bit int cheap turbines for underdeveloped rural regions you will find a lot of two-blade designs. But in the long run three-blade designs are more cost-efficient due to the fundamental mathematical priciple (and not because of the sheer cost structure)
I agree with you, it's lacking. I used a college text book for reference, but I left out most of the information because I was trying to keep videos below 3 minutes at the time. I will probably remake this video further down the line.
+Real Engineering wow, that was a quick reply. The cost factors are very dominant and it looks like two - blade designs seem to be reconsidered for offshore parks. But the math of the forces just fits the topic and tone of your channel much better ☺
I'd like to know the text title. Glad to see you notice it is a little over simplified. I know enough to see this myself, but have not read much on this subject. In particular the arm of the leaver related to torque on the system. The "Lift" in the radial component differs with the distance from the spin access. Obvious, but it needs to be taken in to consideration in the comparisons of designs of varying blade numbers. I think a good Aeronautical background helps and I have a little.
The only constraint on the blade spinning speed is the seped of sound. The tips of the blades are travelling close to the spped of sound, it is the main criteria when engineers optimize the design. Also gyroscopic forces are wild on two blade designs - they cause wery unpleasand type of vibrations - this is why three blades are preferrable even on very small household turbines.
I thought he was going to talk about primary and secondary balance, instead he basically just did a cost-benefit analysis.
I would have preferred to have a more Technical Explanation of what the Advantages would be on 4 or even 6 Blade Turbine rather than just writing it off with Cost... i know Costs count, but the Technical aspect should be the primary aspect of the video.
That said: will you be doing a Video on the "Vertical Axis Wind Turbines" soon?
because in theory, they are a lot more efficient and cost effective than the classic Horizontal Axis Turbines, yet you don't see too many around yet... WHY???
+CrazySteTV
He explained it: when adding more blades, the drag and the cost become a problem. It is not worth adding more than 3.
vertical axis rotors are not more cost effective, no clue where you got that from. they are also hard to built in big scale and because of their small form factor always closer to the ground thous slower and less steady wind to work with
+Robb Stark they are Simpler to Construct, they have a big advantage as they can take wind from multiple directions without need to rotate the mechanism in the Wind direction, which means a lot more efficiency even if the Wind blows in contrasting directions; they rely on 2 bearings, of which the most stressed is close to the ground and of easy maintenance not to mention the actual GearBox and Generator are at ground level, making maintenance a breeze.
cleantechnica.com/2011/07/14/caltech-vertical-axis-wind-turbines-boost-wind-farm-power-efficiency-10x/
at ground level there is less wind, why do you think nobody is building them on a meaning full scale when you claim it's more efficient design? it's absolutely fringe and unimportant
the authors are talking about efficiency in terms of space claiming that the area efficiancy is 2-3 W/m² which i assume they came up with using some kind of abitrary circle around the machine that is , the efficiancy of a horizontal turbine based on the vertical plane the blades cross is about 250-450 W/m². so yeah the article is grossly missleading to create a hype around a technology that was used since the persian empire like it's a game changer :)
More blades mean more "Solidity" (a factor of wind turbines). It is the area of the inscribed circle of the blades length divided by the frontal area of the blades as experienced from the axis of rotation. More blades would mean more solidity and this would block a large part of the airflow, lowering the effectiveness of the next turbine in the row. Also the effectiveness is more affected by the length of each wing as there is little to no torque at the base of each wing, while adding an extra wing would increase the rotational mass, the cost of the construction when a similar increase in weight and cost invested in wing length would have better performance!
PS: Two blades have balancing issues as the height of the turbine oscillates, so will the torque from the wind and to make matter worst when one blade of a two blade turbine is at the top position the other blade is in front of the mast having no air flow at all, so both the rotating assembly would have a knock like imbalance when a blade passes the mast, AND the whole turbine would have a great oscillation from the oscillation of the torque transmitted to the mast!
You're welcome!
Actualy that isn't the case. Two bladed turbines have problems with vibrations when pivoting when wind is changing course.
On top of a couple other things offered in the comments... ^^this^^ too. The rotational inertia of the whole nacelle yawing (to direct the turbine into the wind) will shoot up and down as the blades spin. It's at its maximum when the blades are horizontal and at its minimum when the blades are vertical. Thus, the system will shutter as you try to yaw the nacelle.
sjoormen1 hhh
a nice simple video, but you eliminated a 4-blade design based on "will only provide marginally more performance"
any reference for that?
also, if sound is the issue, does a 2-blade design make sense in off-shore wind farms?
+MS4E All the information is sourced from the Number of Blades section (page 340) in my referenced book. Another video by Learn Engineering stated it improved performace by 0.5%. I couldn't find a reference for that anywhere, so I didn't want to repeat it, but the idea is correct.
Sound is just one issue, like I said higher speeds means higher loads. There is also a problem with teetering, for 2 bladed turbines. The hub needs to be able to tilt on it's rotational axis, because the 2 blade loads vary as the blades pass in front of the tower. 3 blades don't have this problem.
Right now I can't afford to make these videos too long, but as time goes on I hope to be able to hire animators and writers to make real documentary style videos to cover as much as possible. Thanks for the questions, I will always try to answer any questions like this in the comments.
+Real Engineering my understanding was also that a higher number of blades reduces the efficiency per blade. Every blade is travelling the wake of the blade in front of it, and so the most efficient is the single blade. However, a one blade turbine is less effective, for the reasons explained in your video. So it's a trade off between efficiency per blade and the number of blades that makes 3 the sweet spot.
Gohan6 2 blade design can’t pivot in wind direction
I don't get why people complain so much about engineering videos on internet, taking everything down to the "wrong" details. This is not a college lesson, it's meant for people with no background to take some interest, and to actually learn something in an easy way. I think the way he explains the basics in 3 minutes is perfect.
I really like your channel but was rather disappointed about this particular video. When you change the number of blades many other variables can also be changed to compensate for a fixed say energy output. You only gave one argument each but didn't properly argue why everything else stays the same. For the four blade you say the cost increases at a marginal increase in the performance, but you could also make each blade smaller and in particular all your arguments for the two blade variant apply (less speed and less noise) which would even make the four blade variant look better.
Holger Brandsmeier definitely not my best, far to complicated a subject to explain in 3 mins. Will probably revisit it somewhere down the line.
Also forgot to add in harmonic balance at higher rotation speeds
This all makes sense but you could make the exact same argument comparing 3, 4, and 5 blade designs and conclude that 4 is the best.
Not when talking about absolute numbers. If a 3-bladed configuration is better than a 4-bladed one because of the cost versus power-generation, then why would you even compare it to a 5-bladed configuration still? More so, you can't make the same argument by your logic when comparing 1, 2 and 3 blade design, can you?
I agree but the video didn't mention absolute numbers. I was just trying to say that the reasoning in this video is reasonable in a relative sense but it needs some numbers to justify centering the argument at 2, 3, 4 blades.
Curiosity says:Theoretically, a one-bladed turbine is the most aerodynamically efficient configuration. However, it is not very practical because of stability problems. Turbines with two blades offer the next best design, but are affected by a wobbling phenomenon similar to gyroscopic precession.
Since a wind turbine must always face into the wind, the blades will have to change their direction vertically when there is a shift in wind direction. This is referred to as yawing. In the case of a two-bladed system, when the blades are vertical (i.e., in line with the tower and the axis of rotation) there is very little resistance to the yawing motion.
But when the two blades are in the horizontal position, the blades span a greater distance from the axis of rotation and so experience maximum resistance to yawing (notice how a spinning figure skater slows down when they bring their arms away from their body. As a result, the yawing motion starts and stops twice per revolution, and this leads to stress on the turbine due to blade chattering.
On the other hand, a turbine with three blades has very little vibration or chatter. This is because when one blade is in the horizontal position, its resistance to the yaw force is counter-balanced by the two other blades. So, a three-bladed turbine represents the best combination of high rotational speed and minimum stress.
because it looks like the Mercedes logo and it looks cool
ayyyyy lmao
Haha
3 for the Trinity...... The Father, Son and Holy Spirit..... pray that it does not fall apart.
YouSurf lol😂
And four blades looks like nazi
At least the comment section was informative, so the video wasn't a complete waste of time.
jerk
+Ariel Sproul don't call him a jerk, ya douche
aguyandhiscomputer : / really your saying that I'm mean when he was hating on the video
you don't know how this works, do you?
aguyandhiscomputer =_= fuck you
I don't care at all why do they have three blades, but Real Engineering videos are so interesting so I will watch it anyway. There is always a lot of interesting peculiarities described in detail but very understandable.
Wonderful, as always.
+exurb1a - The same goes for you. Love your videos.
+exurb1a Thanks bud, loved your most recent video....even though I am the complete opposite
+exurb1a Please, the main reason has not even been mentionned! It's essentialy dynamic balance, the odd number of blade is limiting vibrations
Nice video but please don't use Centrifugal force as an explanation for something. It is a fictitious force and therefore has no effect on anything really. What you more likely meant was Centripetal force which causes the feeling of Centrifugal force. Just bringing it to your attention.
You managed to get that backwards.
When was kid, I used to build blades (from wood) and get them in garden for fun. Was aiming for ~80 (early)-100 (later) cm long (4,5-5 cm x 1,5 cm dimension, used knife to cut wood from both sides to get better wind pick-up for front side and reduce weight for back side - felt fragile but was sturdy enough for many months) blade with some 105-110 g weight each + central wood piece to hold that all.
3-blade version was lightest but also not great at picking up slow wind (since at ground level difference between up and down can be big with all turbulence etc.). 5-blade version I found perfect combination (for that size) - it picked up speed quickly and turned smooth (and looked more cool when was not spinning, hahaha). And same time at strong winds auto-turned sideways to slow down (design by accident). (still had to take down when storms were coming). Good memories.
Are you sure it wouldn't be better to have 3.14... blades ? How, I don't care...
Funniest comment yet, thank you.
You are being pious and your argument is circular.
omg nice one👌😂
I love your name!!
+Humble Evidence Accepter I thought it was pretty rad.
This is a great video. I think it adequately explains why a three-bladed wind turbine is preferable over a four-bladed one. The primary reason that two-bladed wind turbines are not common, however, is that the rotation of a two-bladed rotor is unstable.Any three-dimensional object, with three different moments of inertia, has one unstable axis of rotation. If you're not familiar with moments of inertia, think of it as mass distribution. A cube is identical in all dimensions, and therefore, has three identical mass distributions in all directions. As a result, a cube does not have an unstable axis of rotation.Your smartphone, however, has three different dimensions; the largest is the height, the shortest is the thickness, and the intermediate dimension is the width. Try throwing your phone into the air three times while giving it a spin. Each time, get it to rotate about a different axis. You will notice that it rotates without any surprises when spinning about its height axis and its thickness axis.However, you will also notice that it is impossible to actually spin your phone such that it will maintain its rotation about its width axis. No matter how precise your throw is, the phone will start out by rotating about its width axis, but the rotation will soon become unstable and the phone will begin rotating about the remaining two axes.This phenomenon is call the "intermediate axis theorem", and it is difficult to explain verbally. Those that are interested can lookup Euler's equations of motion for a mathematical explanation. See the following video for a visual explanation:czcams.com/video/-Si6iRL5Fj8H/video.htmlow does this relate to a two-bladed wind turbine? The rotating components in a wind turbine are the rotor (which includes the blades and the hub) and the main driveshaft. If you draw a bounding box around a two-bladed rotor and its shaft, such that the box captures the outermost dimensions of this subsystem, you will notice that the shape of the bounding box is identical to the shape of your smartphone. It has a large height, a small thickness, and an intermediate width. In other words, the mass of the two-bladed subsystem is distributed differently in all three dimensions.Adding a third blade (or more) eliminates this instability problem, since the additional blades make the mass distribution identical in two out of three dimensions. Imagine taking your iPhone and reshaping it such that its width is now equal to its height. This change in geometry will eliminate the intermediate axis, and therefore, will eliminate the effect of the "intermediate axis theorem".
You forgot to mention that two blades results in mechanical fatigue ant the hub due to standing waves produced when one blade passes into the shadow of the tower. Three blades cancel any standing waves by splitting the energy to the opposite two blades thereby canceling any resonance.
Shadow of the tower? Aren't these contraptions facing the wind so the tower is behind??
@@tomkarlsborn2384 Yes, the tower is down-wind of the blade, but lower blade suddenly becomes 'unloaded' as soon as it passes in front of the tower while the loading on the upper blade remains unaffected (and is much greater). Throughout, there is a general wind shear affect across the rotor with the wind speed being higher with height (although this is constant). The result is a continuous eccentric loading 'blip' each time a blade passes the tower (in a two bladed design) that has to be accommodated by by some means , typically some sort of teetering/hinged hub design to absorb the forces.
Why the hell there is a lot of hating comments on this channel? ,what is wrong with you people ? ,this guy tries to educate the public with an interesting and easy way if you don't like this kind of subjects just don't watch the videos it's that simple ,hey man don't listen to them and keep the good work ,best regards from Palestine
What is the marginal increase in performance by adding a 4th blade? How do you know it's marginal?
fluid dynamics. 3 bladed designs are quite near the maximum theoretical efficency possible for a turbine rotor. The effect of adding a 4th blade would be marginal
Correct, for blade sizes such as we use on wind turbines, operating in air at about 1 atmosphere of pressure.
But the poster of this video knows NOTHING about this, and uses a silly null argument to dismiss 4 blades summarily.
I don't need you guys to reiterate the video. I need you to tell me WHY
Economics being a null argument? Ha.
It is, if all you say is "it's uneconomical". That's not an explanation. You might as well just say "because".
Regardless of what you think about the video, it does raise the question of "why." That is always good!
So does having more blades mean the turbine will perform better? Ignoring costs for a moment, I just want to make sure I understood this properly.
yes
no it will not. for highest efficiency, the blades need to have airflow that's undisturbed. adding more blades causes surrounding air to get more and more turbulent. this is why planes only have one pair of long narrow wing instead of a couple of short ones
+w8stral2 Soo... why don't we use 2 blade turbines then, does that not address frequency problems?
+w8stral2 Thanks for your response, these are the answers that should be in the video.
The example used to show what happens when there is a brake failure, is actually from my country, I lived not far from that turbine when it exploded.
0:19 Was one of those just photoshopped in? XD
Perhaps
That's weird...
There must be some serious experiment going on...
😂😂
The major explanation for this fact isn't shown in the video nor the comments here. The point is that three-bladed turbines may achieve the best power coefficient (Cp) which is above 0.5 and below the Betz Limit (maximum efficiency ANY device may reach when converting wind energy -- 59.3%). The thing about balance and mechanical stress is also true, although not the main reasons for the widespread use of three-bladed turbines. For further info just google: Curve Cp vs. blade number.
How about which is better: a straight propeller design that has to turn to face into the wind OR a spiral design that always has a portion of it always facing into the wind?
Fantastically interesting. My mum worked for the old wind energy group in the UK way back. They made 2 blade turbines. Mum left before they became obselete but the point abt long term stress on the structure from yawing is super interesting to note!
Q: Why Do Wind Turbines Have Three Blades ?
A: They all love Mercedes Benz cars.
*****
:-)
Edward Griffin funny
Abirami Shankar
T Y :-)
There's some important aerodynamic reasons missing from here. There's a tradeoff between maximum power that can be generated throughout a range of wind speeds. As the number of blades goes up, the max power increases, but the range of wind speeds over which you can achieve that drops. Three blades is ideal because a wind turbine needs to be efficient for a range of speeds.
Great video thank you. Always wondered why they did not have more blades.
I just happened to stumble across this channel while looking at videos of the engine swap I'm doing in my car. I love it!!!! Very informational without being crazy long. You, sir, just got another subscriber!
Aaaand another video where the question isn't answered.
And physics
Very awesome to see that the first scene of this video is at the Zaanse Schans in the Netherlands, an area where I grew up nearby. I biked past this view daily for nearly 6 years.
Just look and learn much more about it from Avasva .
I don't mind the noise, it's kind of metronomic and soothing.
The speed regulation also helps maintain the cycles of power generated to comply with the national grid.
Good video dude, keep up the great work.
Loved your Eddystone light house video.
please make a video explaining why centrifugal force doesn't actually exist. Interesting topic.
I made the exact opposite video! czcams.com/video/im-JM0f_J7s/video.html
In that video you state misconceptions as facts and it would be better to not advertise that video any longer.
MaxMental_17 - from a physics perspective, it's pretty straightforward. It is generally defined as the conservation of angular momentum.
Birdman needs a slap.
Real Engineering r
Another aspect of the explanation is 3 blades counteract EACH OTHER during changes in yaw (yaw = directional aim for the entire rotor), whereas 2 blades transmit the forces resulting from changing directions to the bearings, tower, etc. A two-bladed rotor changes direction easily when vertical, and hard when horizontal. Old-timers call the resulting percussive hammering "yaw judders" or "chopping around the corner". That's why 3 blades run smooth, while 2 blades will shake the machine apart. And the reason you only need a few slender blades, rather than filling the whole circle with blades, is they go so fast that it doesn't take very much blade to extract all the available power from the airstream.. Many attempts at two-bladed turbines use teetering hubs with the rotor downwind of the tower, to decouple the yaw judders from the bearings, have been tried, but few, if any, have proven to be a good solution. As the video points out, two-bladers go just a bit too fast for effective noise control. Because two-bladers go too fast AND shake themselves apart, the extra speed makes the shaking that much worse. When you want machinery to last many years, smooth operation is key.
What about no blades?
Like a Dyson!
No blades is indeed optimal! None of these bird-slicers will ever produce enough electricity to pay for their cost of production, maintenance, and use of land.
You mean aside from wind power having, last I cared, the lowest lifetime cost per watt-hour of any form of power plant?
Actually there is a wind turbine with no blades, it's system is a bit different but it exists!
The power output is so miniscule as to be irrelevant.... for now. The technology is advancing so quickly, that maybe in 10 years or so it may become a practical reality.
I teach economics, and am thinking of using this video in class. You stumble on a bunch of economic concepts that I can point to and say "Here it is in real life."
The economic question I have (that perhaps engineering can answer) is:
Once the initial manufacturing cost is sunk (irretrievable), won't the 4-bladed turbine last longer due to less wear-and-tear? (The reverse of your argument against the 2-blade)
Downside:
The total cost to build 4-blade will be "hundreds of thousands of dollars" more.
There will be additional costs to make the structure sturdy enough to carry the additional weight load.
There will also be the cost to re-design, re-engineer, and build the 4-blade unit.
Upside:
There is an increase in efficiency... small, but measurable.
There will be a longer product life due to less wear-and-tear.
There will be reduced maintenance costs due to slower moving mechanical parts.
So, there will be a greater initial (sunk) cost. However, there will be a greater long-term output, lower maintenance costs, and a longer overall life... leading to potentially greater profit. Longer term to be sure, but Turbines are not get-rich-quick operations. All this assumes that the 4-blade will have a longer productive life than a 3 blade.
With this in mind, does the engineering match the economics? Will the 4-blade unit as I describe it last significantly longer? Or am I mis-stating the assumption about "wear-and-tear?"
Thanks mucho!!
+Michael Torguson Not sure if this will answer the question, but with a 4-Blade unit you will have a higher initial cost with slightly higher revenue (think cash flow over a period of time) and it seems that you have an overall higher cash flow with the 3 blade systems. I don't see 4 blades having lower maintenance costs either. Blades will be less efficient due to traveling too close to the wake of the previous blades. Also think about weight and rotational inertia. Less efficient will mean high speeds and more wear on bearings and shafts. This will lead to more over hauls (again think cash flow diagrams) or higher initial cost to strengthen supporting components. More robust bearings and shafting will also cause a drop in efficiency.
Overall this would mainly be two scenarios where you have 1. high initial cost, higher maintenance, higher profit and 2. lower initial cost, lower maintenance and lower profit. The economic lesson would be in choosing which is the most feasible. Hope this helps! I'm not an economist by any sort, but I am an engineer/project manager and enjoy thought experiments.
+Tyler Scrivner I had not even thought of the leading blade's "wake" being a factor... but it makes sense! That would cause buffeting and drag, and wear the bearings?
I was thinking about the rotation of the hub: 3 blades move faster, wearing more; 4 blades move slower, wearing less. But, that would bring another economics term into play: Ceteris Paribus: All Else Being Equal. Economists love to make one change to a model, presuming all other factors will stay the same. (We should know better, as no change can be done without effecting other systems).
Thanks!!
This is the noise a wind turbine makes "Shows us a clip that shows how quiet they are*
look, that whoosing noise is very very annoying, if you had a wind turbine in your back garden, then you would get rather annoyed within 1 hour.
@@56independent42 I'd be a lot more annoyed by smoke of coal or dangers of nuclear tbh.
@@sh4dy832 nucular power is actually extremely safe. only 3 large accidents have occured, wich is a lot better then any other form of eneg=rgy production.
In the early 70's in the infantsy of large wind turbines: One of the factors that led to 3 bladed propellers was the fact the 2 and 4 bladed propellers were exceedingly hard on main shaft bearings. This was because the wind velocity differential between 100 feet (the propeller tip at the low end of the swing) and 300 feet (the propeller tip at the high end of the swing) would create enormous lateral stress on the main shaft bearing. The use of a three bladed propeller effectively neutralized this effect. All other factors aside, the three bladed propeller was the only configuration that would provide any degree of mechanical reliability in windmills that were large enough to be affected by (altitude) wind velocity differential.
This one is very incomplete.
matekochkoch yeah, but he said in the comment section that he will remake is someday because of that reason
A girl once asked me this question now I can answer her. Thanks man. Keep up the great work.
Dude, you didn't explain anything. Saying "4 blades is less cost effective." just begs the question. Obviously, the answer to the original question is "other numbers are less cost effective". The REAL question is WHY N ≠ 3 (e.g. N = 4) is less cost effective than 3.
Best CZcams channel ever...
every single argument you state that advantages 3-blade vs. 2-blade, can also be used *as is* for the 4-blade vs. 3-blade argument.
Yet you discard the 4-blade design with a quick handwave blurb that contains NO quantitative data.
i.e. You actually do NOT state why turbines have three blades.
I am glad you feel the need to talk about renewables, but PLEASE know your subject before telling the world how it is. I hope you can learn more about the subject and come back with better reasoning.
All the best
BUT WHAT ABOUT 100 BLADES AT 500 METERS LONG EACH BLADE
+BoomBrush ill try that in my garage next week should work ;)
If you aren't being sarcastic, there are no materials currently known to science that supports 500m long blades that spins and it would be too heavy for the wind to even turn it
+Kai beyond that, the tips of the blades would probably break the speed of sound
Real Engineering breaking the speed of sound wouldn't be a problem because I'll be building it in my vacuum chamber
+Pieter Schreurs Hahahaha a, brilliant. Let me know how it goes
A video that explains Good Engineering ... The best solution considering time and cost
Wasn't very informative, I expected some physics of airflows and such
you are legitimately my favorite channel.
your info is far too generalist and you are throwing in your own assumptions. this my friend is what you call a token effort.
Please elaborate in a follow-up video. We are spoiled now with your more recent videos and have come to expect real meaty explanations. We will, of course, be very appreciative of your efforts and continue to provide vast praise for your efforts. I have recently subscribed, just after watching several videos because I love engineering topics.
There are also one-bladed designs available!
precisely my thought
Well that'd be an extrapolation of the 2 bladed design which has already been shown to be less cost effective than the 3 blade. Some smaller wind turbines are 2 bladed, as I understand it that's because the construction is easier and only needs 1 crane for assembly so they win in cases where the capital cost is critical.
It's also about reducing vibration. With an even number of blades, as in the 2-bladed design, when the lower blade passes by the tower it is masked from the wind. This is at the exact time that the upper blade is receiving its full amount of wind. This effect will set up vibration in the tower. With an odd number of blades, as with the 3-bladed design, there is not the same vibration effect as when the lower blade is masked by the tower there are still 2 more in the airflow to smooth out the effect.
not happy with this explanation
The biggest benefit to the three blades is the reduction in vibrations when the wind quickly changes direction (as it usually does). When the two blade design is vertical it can change direction very quickly and easily. When both blades are horizontal it changes direction very reluctantly. Thus you have a vibration problem when the blades quickly go from the horizontal position to the vertical position. With the three blade system the blades are never exactly opposite each other and this helps to minimize the vibrations. I have had a 3 blade wind generator up for almost 18 years now and I watch it in high wind conditions. I also fly smaller aircrafts with only one or two seats and there again the three blade system is better.
Awesome, subscribed!
+wrenthereaper wo, wrenthereaper.....love your work. Only just started learning after effects, but hope to kick it up a notch as time goes on. I need 3DS Max in my life
Real Engineering Yeah dude! It's just a matter of trying to do shots you don't really know how to do, and figuring it out. It's a lot like engineering, actually!
Hi,
i took a class in modern wind turbine physics for a semester (about five years ago) and a another factor for three wings vs. two wings I remember is, that the tower is messing with the down stream wind speed.
Basically, on a two winged wind turbine, the load forced on the upper wing will be much* higher compared to the lower wing when that one is in front of the tower.
It is also higher compared to the sum of the two upper wings of a three winged turbine
The effect of this would be a higher rocking of the turbine for a two winged turbine than a three winged turbine.
Which can cause higher wear and tear for a two winged wind turbine.
3 blades look better. That's why. the end.
And the designer only had three fingers left after playing with models of them.
yep, two blades looks just plain wrong and, well, disconcerting when they are turning.
+Andrew Holdaway I thought this was the main reason 2-blade turbines fell out of fashion. The unsettling moment the blades align with the mast, or something.
Love your user name!!!
Out of world
Cool we have dozens of these in a small island off the coast of Anchorage and they are beautiful!
Q: Why Do Wind Turbines Have Three Blades?
A: It's better than other numbers of blades, thanks for watching
Good video. I'm a Brazilian and I live in Brazil.
Those dont sound too noisy.
They don't make a lot of noise, I lived near to a bunch of them and never heard it. Noise is just used as an argument for people who hate renewable energy for some other reason. Try living near to a busy road intersection and you know what noise means.
I do live near a busy intersection. It's shit.
I'd rather live near a soft, constant dronning then that.
madcat789
If they do make a noise it's not much different than the wind blowing the trees or the sea and mostly people can live with that.
Then thats something I can get used too.
Most of a HAWT comes from the converter assembly. But get 30 yards away, and you hardly hear anything. On most sites, if a turbine is making noise due to a problem (deteriorated blade, a bad bearing in the generator) and a landowner complains, it will be shut down until the problem is assessed.
0.59 “Fewer” not “Less” Sorry to be a pedant on your otherwise excellent videos! You are worth it !
it felt as if I should be getting smarter, and yet i haven't learned a thing... =/
I learned a lot about this interesting subject from your video and from the many technical comments it spawned. Thanks.
And that is how the wind destroys a wind turbine.
That is the old tech from old footage. He got this one point wrong. I commented about it under his comment. Including that footage misrepresents current safety standards and state-of-the-art technology.
Marcellus Jacobs is the engineer who figured out the three bladed propeller system for wind generators back in the 1930s. Look it up. His successful basic design is the still the one that exists today in the many patented improvements. No one needs to reinvent the wheel. It's still the gold standard for ANYTHING wind generated.
Your explanation of the problem with a 4 blade design 'adding a 4th blade provides such a marginal increase in performance' completely fudges the point. the answer to the question you pose about why turbines have 3 blades hangs on the question of why the increase is marginal and how marginal.
Why does such as a steam turbine have 100's of blades. why is the goldilocks zone completely different in that scenario?
The graph at 1:18 shows absolutely nothing.
The turbine you showed failing, failed because the blade hit the stand. which is probably the most important factor, together with height in limiting the blade length, which in turn is why we use 3 blades not 2.
Your videos are normally quite informative. But this is just, well nice looking garbage.
I think it's mostly because of turbulence : the more you ad blades, the closer they are to each other thus more influenced by the turbulence behind the previous blade, causing it to be less effective (unstable airflow) and it could even cause them to vibrate more. Even thought those are just suppositions I think it could explain the differences between steam turbines and wind turbines (you have so much power to deal with in a steam turbine that you are more likely to see the basic equation more blades = more power to actually work)
Close but what is missing? I am surprised that no one mentioned the Betz limit. The mechanical forces answers were only partially correct, you can always make things stronger/stiffer and avoid natural frequencies. But the Betz limit is the physical limitation of getting mechanical force from wind and it is limited to 0.6 or 60%. Three blades gets you to 55+/- and four only adds a few percent, so the limitation is better looked at from this physics limitation which is optimal for cost and design.
One little thing is forgotten:
The more blades the lower the induced drag. Ref.: Prandtl, Betz. 1926. It's "hidden" in the tip loss.
But mainly- absolute correct, it's a cost and optimization issue.
0:22 When you get lost as a white boy in da hood.
A table with 3 legs are always stable.
Table with 4 legs, legs need to be the same hight (exactly) so it wont wobble.
Apart from the blueprint background that gives the impression of an engineer, which they stopped using by the way.
Nice animations and thats about it.
I liked this video, until he wished us happy earth day.
HAAAAAAPPY EARTH DAY!
+Real Engineering Earth day was invented by a Philthydelphia HIPPY by the name of Ira Einhorn. He was known to be abusive to women. One day his girlfriend went missing at the same time he flew in a kerosene smoke belching jet to Europe. A month later the tenants of the apartment below him started to complain about a fowl smelling liquid dripping from the ceiling. Upon investigation, police found Einhorn's liquefied decomposing girlfriend rotting in a trunk in his closet. Einhorn, a good example of the average Inviromentalist LIBTARD HIPPY.
FUCK EARTHDAY BURN TIRES ALL DAY!
Einhorn claims to be the creator of Earth Day. Many organizers deny it and credit Gaylord Nelson as the founder. Even if it really was Einhorn's idea, using his crimes as an excuse to shit on Earth Day is fuckin stupid.
How about laughing at Earth day because of the morons in plastic kayaks protesting oil tankers?
Those kayaks were made using oil, dumbasses.
@Викентий Мадзин
Basically we should damage the earth because the alleged inventor of an arbitrary earth day was an asshole.
More like a good example of the average ignorant RIGHT-WING FANATIC.
Yes, another smart channel found on the ocean of videos.
Come on. You can do better than this video
+Daniel Björkman Absolutely, the videos are getting better I hope. This video taught me a lot.
What I ment to say that is that I much more appreciated the other videos you've made. The concept of basic efficency is too simple for a video like this. If you could explain in a graph or make intuetive comparisons then the video would get better scientific depth. Keep on the good work!
Andrew Gerrad the president of the European Wind Energy Association, said in one conference speech that 3 bladed wind turbines are the result of human preference. 2 blade wind turbine would be way cheaper to move from one place to another. You could put it together in a factory and ship it to the site in one piece. When with 3 blade system you need to install the blades on site and that is really hard and expensive. But for some strange reason people hate how 2 blade turbine look like. Gerrad also said that now that offshore wind turbines are getting more common, wind turbine engineers don't need to think so much about the looks of the turbine.
Sorry for my english I'm from Finland.
There is no such thing as centrifugal force - there is only a centripetal force. Get it right "real" engineering.
Go ahead and watch my artificial gravity video please. Your understanding of the term is off.
xkcd.com/123/
The first thing they teach you when you learn about 'fictitious' forces in the Classical Mechanics module of a good Physics or Engineering course is that they aren't really all that fictitious. Hop in a 20 G centrifuge and you will believe in centrifugal force.
Areo Hotah "Centrifugal" force is simply centripetal force exterted on the body from the reference plane of the body being moved. It's a mis-use of the word. It's redundant, and for this to be an "engineering" channel it needs to be more accurate, that's all. Centripetal forces tear this windmill apart, not "centrifugal"
Dominic centrifugal force is a reaction force to centripetal. A force without a reaction force causes an acceleration, not a stress. One cannot exist without the other. Centrifugal is the correct term to use. This is why I made my artificial gravity video. The idea is being taught very poorly in schools.
I really appreciate your videos, very interesting stuff! Currently studying for my bachelor's in mechanical engineering.
+John Tyrrell Fantastic. It's a tough course, keep working hard. My bachelors is in biomedical engineering, basically the same course, just with some medicine classes thrown in. Feel free to send me any suggestions for videos you would like to see
we gonna talk about how centrifugal force is not a real thing or?
Really authentic content. This is just the kind of channel I will want to browse.
Can you guys make a quick video of how does a quadcopter works? The physics behind the stabilization, turns etc.
CENTRIFUGAL FORCE ISN'T A REAL FORCE, pickup a physics book mr "Real Engineering".
xkcd.com/123/
+Krieger heh, thank you for that humor sir
It is to engineers. Go and hold on to one of those blade tips while they're spinning at full speed and after your arms give way after 0.2 seconds, do you fly inwards or outwards?
By the way Krieger was pointing out that you're wrong.
It depends on what reference frame you're in. The centrifugal force can be real of fake; it all depends on the reference frame.
Its never a "fake force". In my experience that explanation is usually offered by those with little understanding in physics who are simply regurgitating the words of their high school physics teacher (who was also wrong) in an attempt to seem knowledgeable.
Centrifugal force can be thought as the tenancy of an object confined to a circular path to continue in its instantaneous tangential direction, in accordance with Newtons first law. It can also be thought of as the reaction force exerted by a body in circular motion in response to the centripetal force, which is the force confining the body to its circular path. Regardless of how you think of it these two behaviors don't change depending on your reference frame, that's a fairly dim witted explanation in my opinion.
Thanks for sharing this...it really continues the great universal phenomenon, "less is more''!
I have just seen your (airplane) videos and now I can't stop to see your videos. They are very good researched!
I live near the SoCal beach rail. At night there is a freight train that transports a lot of these blades. They are huge and are set onto special rigs that cover 2 train cars.
This is gives a complete answer without any questions left behind. ☺️
Curtiss-Wright figured this out late in the war, when incredibly large high performance piston engines were being built, just before the Jet Age. Too many blades, and you have a flywheel, with blades getting in the way...this isn't too bad for a low RPM water pumping mill. But at the other end? Even very small differences in weight will cause a two bladed design to tear itself right out of its motor mounts. This is why they went to three blades. And the old "Jacobs" windmills that were common in Rural USA before the grid also used the far superior three blade design.
Very good video. Will use this in future projects.
There would also be the incremental cost of blades and generating equipment vs. the cost of tower and other infrastructure.
I'm sure that some review of why aeroplanes largely settled on 3-bladed propellers would be revealing.
I would go for the 2.5 blade option
It just occurred to me, that there is something distinctly off with that theory that 3 blades would help reduce the stresses that occur from one blade getting no wind when it passes the pole, or mast or tower or whatever it is and its name is, at the lowest point of the circle these blades describe, and that the idea that a 3-bladed design would involve a reduction in the distortion of balance (and with that extra vibrations and extra stresses that play onto several parts) simply can't be right. When you think about it, with a 3-blade setup, there are TWO blades getting full wind whilst one gets none each time, so now 2 put up full force against that one blade that produces less our none for a short while, instead of the one active blade that is oriented oppositive of the one that momentarily is inacive each time as it happens in the 2-blade design. The relative stresses are theoretically up to twice as big! I think it would be fair to conclude: 1 it may have got more to do with other variations and effects that might cause vibration, trembling and lack of balance, such as the fact that even over a distance of dozens of meters the force/speed of the wind might vary; 2 it might have got more to do with the actual surface of the blades (seems that although too long blades come with the problem of too high tip speed in up to several hundred kilometers/hour, blades that are constructed in a wider fashion like was done with the old (old-fashioned) wooden windmills, for some reason ALSO again is not favored by designers); 3 to overcome or at least significantly reduce the stress caused by the unbalance coming from one blade putting up no counter force for a short while each time, you would at least need 5 blades, and preferably even seven. In a setup that sports 5 blades, the blade that momentarily stops producing force (and therewith counterweight relative to the other blade or blades) is always accompanied by TWO other blades that ARE ACTIVE AT ITS OWN SIDE (halve if you will) of the axis so a construction like this puts up most of the oppositive forces that out takes to balance the two remaining active blades that are on the other side of the central point of rotation. As opposed to there being two active blades OPPOSITE to it on the axis and NONE on its own side in the 3-blade setup. This however gradually becomes much more difficult to mount to the central axis of the thing, supposedly might be pricier as there is some loss simply related to the scaling difference versus the effective surface created. And, ALL blades have a small part, near where they are mounted, where they catch little or no wind anyway, as the generator housing also blocks the wind
You should also mention aesthetics in the remake. Egg-beater style wind turbines are considered "ugly" even though they are more efficient. They're also noted for being deadlier for birds.
Thx for this video cos I love wind turbines
Recently discovered the channel and I like your videos but I would love to understand the concepts that contribute to these phenomenons better otherwise by the end of the video, for example, I still don't really know why the three blade turbine is the best option. I'm not asking for full blown lessons but enough so we can better see the relationship between concept, application, and the specific example. Thanks!
you should add the more immidiate info for 2 bladed turbines which is the wobbling phenomenon which leads to stress on the turbines Tower / gears due to blade chattering while yawing into the wind. A turbine with three blades has very little vibration or chatter. This is because when one blade is in the horizontal position, its resistance to the yaw force is counter-balanced by the two other blades. So, a three-bladed turbine represents the best combination of high rotational speed and minimum stress.