Rosie, I have just stumbled upon this video of yours and I'll come right out and say it. It has tbe best thumbnail a video on TH-cam can have. It poses a great question, It gives the "Tldr" answer, and has your smiley face there so we all know its not more AI created bot content. Love your work mate!
Hi, Rosie! Just want you to know, this is the 3rd or 4th video I've watched from your channel, and all have been nothing short of phenomenal. Thank you so much for taking the time to share your wealth of information and knowledge. Keep up the good work - I'm looking forward for more!
... i find it very hard to explain things to people who aren't on the same level ... You do such a wonderful job explaining complex problems so that i can understand them effortlessly . Thx so much 👍🏼❤️🖖🏼
The reduction gear and generator shape and size (unless stupidly large in diameter) has neglible impacto on the turbine rotors ability to extract power from the wind, however the design of the reduction gear and generator will have great impact on how much of the power extracted by the turbine rotor that can be turned into electrical power.
Gearless elevator machine efficiency ~90% Geared worm/gear-ring elevator machine efficiency ~50% Just from memory because I'm not digging out my notes from boxes (I'm a retired engineering consultant now specializing in sleeping & long walks). There's a formula for geared elevator machine efficiency though and it depends on the sheave diameter so the ~50% varies. Also, these are all worm/gear-ring machines and helical machines are more efficient (I never studied those because they're only used for winding-drum lifts). Electrical efficiency likely depends on the air gap because air has 5,000x the magnetic reluctance of soft iron. Big old D.C. motors had a huge 0.100" air gap. Small modern A.C. PM motors have tiny air gaps like maybe 0.003" but I don't really know exactly. An installer complained that problems with a new one were because the manufacturer told them 0.0005" less steel shim than required so the rotor was touching the stator pole faces, so obviously nothing like the old huge 0.100" air gap. I suppose generators are the same because electric motors and electric generators are the same thing, electric motors also generate electricity during "overhauling" (a situation where the load starts mechanically-pulling or electrically-pushing the electric motor round & round instead of the electric motor mechanically-pulling or electrically-pushing the load).
From the comments I guess that over the last week or so the almighty algorithm has decided to push this channel very hard. I too belong to those people...
I;'ve been for a couple decades trying/sometimes succeeding at building small wind turbines up to 24' diameter but usually smaller. Largely based on ideas and education from Hugh Piggot and others. These days I'm bombarded with questions and bad ideas/designs from folks on the internet. It'd be pretty neat if you could get Hugh on your show. I still build the occasional machine here in the US but only after carefully screening the potential client. Lo've your channel, you're doing it right.
hi, i love the way you brief the whole concept ,its really very helpful. I'm research scholar from India working on the optimization of wind energy as part of my research work.so here i request you to pls give some ideas and technologies regarding to improve the power efficiency at lower wind speeds or variable wind speeds of wind turbines.
Nice vid on Betz! You say "stream tube" I say "cross section". The cross section is the area within the perimeter outline of the turbine as seen from the wind. Flanges, ducting etc, as you said are all part of this cross section (important, not "swept area" as that assumes horizontal perpendicular blades to the wind). In another video I believe (could be faulty memory) you mentioned that Betz didn't apply to vertical axis turbines? I'd be interested to understand your thought process behind that. To me, it's all the same. Cross section, energy in, energy removed, still needs energy to move the slower air mass away...Betz.
not piling up, but squattered to various directions with various velocities, therefore 100% is a limit, not 59% (due to simple pressure differences the air from other volumes would fill the area of stagnating air molecules)
Awesome! It seems crazy to me that you can extract as much as 59% of the energy when the blades only occupy a small fraction of the area of the rotor disk.
You need air flow. Block too much of the air flow and you decrease the velocity of the airstream passing by the blades reducing the kinetic energy available to be extracted.
The Betz Limit does apply to a circular disk actuator ( ie a HAWT ) . The stream tube passes through the blades only once. But in a H-Darrieus lift-type VAWT, the air stream can pass over the blades twice. I don't think, Betz ever considered that possibility. So, would a H-Darrieus VAWT be similar to placing a second HAWT, down-wind of the first HAWT? So, the second HAWT could ( at most ) extract another 59% of the remaining 59% energy, or another 35% (max) ? The combined energy could then exceed the "59% Limit" of the original air stream? Turbulence from the first HAWT would reduce the efficiency of second wind turbine, for sure. Also, a sail boat can "tack" into headwinds and it can travel faster than the incoming wind speed. What if 50% of the H-Darrieus blades that are moving into the head-winds, used this "sail boat tacking" method to extract energy? The H-Darrieus design is a 3-D Cylinder shape, not a 2-D circular disk actuator, therefore the Betz Formula may need a modification for H-Darrieus VAWT's, because of the assumptions made during the formula's derivation?
Thanks for this thoughtful question! You are right that the aerodynamic analysis is totally different for vertical axis turbines than it is for horizontal axis. But vertical axis turbines are less efficient, not more, than HAWTs. I am working on a video explaining the theory of VAWTs, but it will be a couple of months before it's ready. And I'll make sure to look back at your question and make sure I answer all the points you raise when I make that video. One thing that is the same for VAWTs as HAWTs is that you cannot take all the energy out of the wind. There needs to be some velocity (and therefore energy) left in the wind so it can exit the rotor. But a more detailed answer is going to have to wait until the VAWT video, sorry about that!
@@EngineeringwithRosie Yes, I know that a W/T cannot extract 100% of the energy. I did write "... 59% of the energy is extracted ...". The Betz formula does not have any math for ... The wind tube entering the into the front-half of the VAWT, passing through middle of the rotor, and then the SAME wind tube exiting the rear-half of the VAWT. There are some very efficient H-Darrieus VAWT. Especially, the design with variable pitch blades ( up stream blade angle is different than the down stream blade angle ) by implementing a Wind Vane ( ie a tail ). The H-Darrieus can be made "directional" like a HAWT.
Can you do a video about solar updraft towers... there are a whole bunch of effects mixed together: stack effect of high speed air at altitude, heating/solar heating an air flow making it more energetic, the advantage of having the turbines near ground level (could be horizontal or vertical axis. Is it wind power (stack effect at the top?) is it solar? is it a combination? Can you grow crops underneath? (since the airflow is always inbound from the outside, you can add humidity at the periphery, and potentially extract towards the centre.)
I'm amazed to know that so much of research has already been done on maximum efficiency of wind turbine,, But Rosie,, please answer me-why more number of blades are not used to enhance the efficiency?
@@EngineeringwithRosie sorry dear,, your video tells about twin blades,,but I'm asking about more than 3 blades,, As I tell you,in car engines,,more number of cylinders will make engine smoother and vibration free,,3 cylinder engine is not considered a balance engine,,but 6 cylinder and more is balanced,, So I'm planning to build a 6 or more blade vertical turbine,,or maybe a horizontal turbine with blades(6 or more) installed at 1 feet distance on the shaft,,with blade size 5 feet in dia,, Do you approve this design?
@@EngineeringwithRosie I saw this video,,to me number of blades and their cost is not the big concern,,my ultimate goal is to get higher level of efficiency with compact and balanced design,, So I want to know if 6 vertical blades of stainless steel will be good or not?
Hi Rosie, thank you for the explanation. Is the Betz limit also applicable for a darrieus type of rotor? These turbines touch the wind both on windward and leeward and are not really a disc from Betz perspective. What do you think?
That is a really interesting question! I am going to find a tidal energy expert to ask (could be a good 1 min video topic too). I suspect that yes it is the same, but I have never worked with tidal energy so I can't say for sure, maybe there is a factor I haven't considered. With aerodynamics, you usually assume incompressible flow below transonic speeds. And incompressible flow is usually assumed for wind turbine aerodynamic analysis. But as blades get longer and tip speeds increase, some researchers are starting to consider compressibility in the blade tip region.
Would be interesting to elaborate if any significant effects on moisture transport towards lee side of windfarms as well as on vetical upward displacement of air flow from slowing down the lower layer (acting as artificial hill). Can imagine this might have implications on thermodynamik of the local atmosphere (e.g. temperature profile)
Excellent and insightful video, once again. Couple comments: doesn't the shroud in your illustration show the opposite (diameter of stream tube hitting the blade being reduced), and the Venturi effect being used to impart a higher fluid velocity/energy to the turbine? Also, assuming it would be cost effective, wouldn't adding more blades extract more energy for the same swept area? Sure, you'd have to deal with the turbulence, but I cannot but think that the 3-blade design is letting a lot of the flow pass through between the blades without being used.
Hi, thanks for your comment! The streamtube is wider upstream with the shroud than it would be without it, which gives it a larger effective diameter than the rotor diameter, so it has access to more energy in that larger diameter. And yes, then the streamtube diameter decreases as it hits the rotor, and consequently speeds up. Probably worth more than the 2 second explanation I gave it here! Thanks for highlighting this, and I hope I can do a while video on shrouded turbines some time soon.
And on the question of how many blades/ how much of the rotor should be covered by blades to get maximum efficiency, that is another insightful question! I talk a bit about it in this video: th-cam.com/video/f3hgB-0rPOI/w-d-xo.html And I will be talking a bit more about it in the next two videos in this series about how wind turbines work. But to be honest it is still probably not a really thorough explanation of why adding more blades doesn't increase energy capture. I have an idea of how I can demonstrate that, but it might take a few months to get it done in a way that is properly satisfying. Keep an eye out though!
@@EngineeringwithRosie It would be interesting to know how much of the available energy per area the blades are actually utilizing, unless it's already close enough to the Betz limit that 3 blades is a good compromise. But like you said in the video you linked, there's always room for improvements as well as compromise choices. Look forward to the new videos and thanks much for the reply.
@@slymartins yes it is pretty close already, about 80% of the Betz limit. And it wouldn't get better by simply adding a 4th blade to any modern 3 bladed turbine. I do plan to get more into why adding more blades (or making the blades wider) doesn't add more efficiency, but it will involve a bit of work to demonstrate it. So it will be some months away! The quick explanation is that if you try to extract more energy by adding blades or making then wider than the optimum, you end up with each blade hitting the wake of the blade ahead of it.
I'm convinced that the efficiency of wind turbines is far lower than its potential. If I were to design a boat that was powered by wind, I wouldn't use a small number of narrow (small surface area) sails. I would use as many as possible, and make them as large as possible, within reason. This current design appears to be the opposite, obviously. The blades are about as narrow as a toothpick (in terms of scale), and this is supposedly extracting nearly 50% of the energy? Maybe 50% of the energy of the air it comes into contact with, but not even close to 50% of the total energy available in the wind for that area. Most of the wind is not even touching the device. I would say, it appears >75% of the air flowing through the area is not impacting the blades at all. This cannot be the most efficient design. It needs to have sails. Otherwise, those old canvas windmills would have been designed in the same way, with tiny little blades, and no sails.
I was confused by this as well. I found these videos, which do a better job of explaining the relationship between number of blades, rotor velocity and efficiency: th-cam.com/video/BQI7AwKDQXk/w-d-xo.html th-cam.com/video/_dpGtOyma0Q/w-d-xo.html
@@somerandomnification The old dutch sail type wind mills were obviously sub-optimal, but that doesn't explain why the modern blades cover such a small area, look at the old "farm windmill" design, it's a lot more optimized and made tons of power to pump water in the old days, has anyone ever seen a direct comparison?
@@somerandomnification I'm not questioning the use of airfoils, I'm questioning the structure to power - (disclaimer, this is total speculation) if i were to build models of the new and antique design I'm pretty sure the antique design would out perform the new design, if I modified the antique design to only have 3 blades the new design would probably beat it, if I were to make another model of the new design with 6 blades it would have ~double the power output, does this not make sense? I realize turbulence could get in the way of the following blade but these designs aren't even close to that point.
@@somerandomnification Again, the efficiency of the design is not in question, we are talking about the power leveraged for the material used, for example - on paper hydrogen is the most efficient rocket fuel, but the larger structure required to use it made rockets that were more expensive then others, or how a sterling engine is more efficient then an internal combustion engine yet nobody would try to use it in a car as the amount of material needed to get the power required would be extreme.
Hello Rosie! I like your explanation videos. Please go on. :-) I am always astonished when magazines or newspapers report new developments with gigantic efficiencies. Very often they forgot wake effects, reduction of energy or the self consumption of systems. Why do they not have a look to the basics before they embarrass?
Curious that Rosie uses the term "stream tube" meaning intangible container of air, the physics of which have been altered by presence of turbine mounted directly in airstream. Why no mention of tangible stream tube, meaning ducting that captures wind, redirects, concentrates to turbine mounted on ground? Imagine a windy seashore (eg. Oregon, Washington coasts) with most wind coming from seaward. String a cable across top of valley, with fabric attached to trap onshore winds. Turbine can be fully enclosed, and running on air captured from entire valley section. Velocity depends on area-ratio of tube mouth to rotor circle.
Concepts like this have been tried. I saw one in Tasmania many years ago mounted on an ocean facing headland, a duct directed the windflow onto a multi blade turbine about seven metres in diameter. Not sure what happened to it but suspect issues of practicality defeated the idea. Multiple conventional three bladed power turbines are now at that location.
Brilliant Rosie and to a very non-technical person very well explained! Do you have any videos on solar panels and how to select the most appropriate please? Many thanks Regards Ian Inverness Scotland
The Betz limit is true mostly for standard HAWTs. This "law" is not as strict as the law of conservation of energy and angular momentum, therefore it can be bypassed. I know the scientific community is very skeptical about such statements, but evidence of exceeding Betz’s limit with an efficiency close to 100% will be published soon. (Such as Francis water turbines with an efficiency above 95%)
Nice video; one question though.. You also mention modern turbine approach 50%. However, i'm a bit puzzeled; if i take a Siemens Gamesa 3,6MW offshore turbine, the rated windspeed is 12m/s. Yet, at this speed the theoretically available power in the 120m disc is roughly 12MW. Therefore, the turbine 'consumes' only say a third; far less then half.. Looking at other models, i see the same. Even the new GE Haliade; roughly a third. Yet all literature mentions commercial wind power nears the Betz limit. Or is this an averaged output used as typology and they actually put larger capacity generators in the nacelle. Can you explain this? Siemens Gamesa haven't replied on my email.. :)
Interesting question. I couldn't find the exact models you're talking about, but the ones I did find were not specifying their rated wind speed publicly. If the rated wind speed is 10m/s not 12 then the Siemens example you list works out roughly as expected. So I wonder if it's an issue with how the generator size and rated wind speed are selected/ communicated.
The only variables in the equation are mass and velocity, Would either change? Mass won't, velocity may increase, but that does not increase efficiency.
@@gregripp I can't see the assumption made by looking at the equation. One assumption I predict they might have made is that the ambient air pressure is the same on both sides of the turbine since that would be true almost always.
Are wind turbines spaced such that the expanded "disk" of air exiting the turbines doesn't interfere? Or is there another factor for spacing between turbines?
Simple answer. When the turbine is in thermodynamic equilibrium with the wind, no more energy can be transferred. Beyond a certain point it would be pushing energy uphill.
What about the airflow which passes between the blades…is that not still at full energy as it leaves the disc? Would more blades not produce more power?
I do have a design that is totally different from any known method of extracting electricity from wind power Once I wipo it I will show you an amazing efficiency
Hi! What if these were made opposite? All wind turbines I’ve seen catch the air and make the blades spin in which generates power right? What if theres a turbine that instead catches the wind it it flows with it? Would this generate more wind? Would it act like a fan?
Did you come up with this question after seeing the latest Veritasium video? If not, then you need to see it, basically a physical manifestation of your questions! I am still trying to get my head around how it works, I don't believe that the video gives the full explanation 😊 When I understand then I might make a video explaining how I think it works, and that would answer your questions too. th-cam.com/video/jyQwgBAaBag/w-d-xo.html
so some other youtuber said that the energy expended to manufacture one wind turbine far exceeds the energy it would ever produce.... is that "horse feathrs" ?
Thanks for commenting! No that's not true. Wind turbines have one of the best energy payback periods of all techs. I will be making a video on the concept of EROI - energy return on investment soon (in a few months) where I can talk about it in depth.
@@EngineeringwithRosie Now all I have to do is decide who i believe.. A beautiful, highly intelligent ENGINEER or some youtube wannabe :) gimme a sec.. i know the right answer.. :)
4:19 I don't understand this, just looking at this clip it seems over 75% of the air will pass by unrestricted, how do they get close to 50% of the available energy? (edit: sorry, just went through the comments and saw 2 others already asked this question)
That is disk solidity and you could have 100% solidity with a single very wide blade like a screw. The rotational speed of low solidity turbines is high relative to the wind speed and a blade effects a volume of flow around it, so the effected air mass is still near 100% Maybe better to think about the diagonal path of the blades through the flow rather than a frontal view. This is a propeller vortex visible due to humidity but similar in principal th-cam.com/video/mk8b8Cv_0kk/w-d-xo.html pause it at 59 seconds note only a few inches of space.
I was confused by this as well. I found these videos, which do a better job of explaining the relationship between number of blades, rotor velocity and efficiency: th-cam.com/video/BQI7AwKDQXk/w-d-xo.html th-cam.com/video/_dpGtOyma0Q/w-d-xo.html
As an engineer, you ought to be able to design an audio setup that produces better quality, more intelligible sound for your video. I suggest you try 1) Move farther away from the hard, flat, echo-inducing wall 2) Move closer to the microphone, so it picks up more of your voice and less of the ambient sound of the room.
Thanks Rosie, Your explanations are clear and easy to follow. Can you recommend a small wind turbine for urban power generation, for a house with electric cars to charge, 1-2 kw? We live in an area where there can be a lot of wind but not steady, Juan da Fuca Strait on Vancouver Island. If you don't want to recommend a brand what to look for would be very helpful, and as quiet as possible to keep the neighbours happy.
Thanks Rosie. I am an engineer and have been working on A VAWT design that works on the principles discussed in your video "VAWT Design". I have been working on this design for 10 years and have developed a computer model for a lift-based VAWT and have discovered several important concepts. I cannot find a mechanical engineering department in any universities here in the US that are working on this type of design. Do you know of any? By the way I think you left out an important variable in the equation you showed for aerodynamic force. Thanks again. Noel Potter
Hi Rosie. I have a concern: by using wind and wave power, we're extracting energy from the world's climate systems, and returning it later elsewhere as heat. Is it possible that this will contribute to the climate change crisis? I've never heard this possibility discussed.
afaik heat has neglicible(and temporary) effect on climate, the problem is greenhouse gasses acting as a blanket, sun heats up earth, blanket makes that less heat can escape, resulting in warmer climate
All the wind energy ends up as heat: if no windmill is present the wind slows eventually due to friction with the ground / mountains / etc So ultimately no net effect
Hi Rosie - loved the vid, thanks. The 59% max Betz efficiency, that must be affected by the residual drag of the generator right? Is the efficiency calculated with or without the gen drag? I'm interested in your thoughts about that. Jerry
That's the theoretical efficiency of conversion from wind energy to rotor energy: with no other energy losses after the rotor. You are both right that the real world efficiency will always be lower due to losses at every energy transfer all the way to the user...
Thank you for excellent video. I have small question, why the disk of wind is considered in 1/2 *rho*A*V^3, while only the 3 blade area is in contact with wind.?
Even the air between the blades is slowed down, without being in contact with the blades. Actually very few air particles get into contact with the blades.
Betz limit does assume the fluid is non-compressible, all fluids are compressible at some point even water. From a very easy one like air, this theorem can't be applied
If you make a blade using the 1.618 golden ratio Diameter and gets bigger untill you Reach 21 or even 55 and Spiral it like Archimedes and make 12 of them you have the Perfect. Turbine to Capture almost 75%
Is wind turbine efficiency typically given as relative to the total energy in the stream tube, or relative to the Betz limit? e.g. if a turbine could extract 50% of the wind energy, would it be called 50% or ~85% efficient?
If i understand correctly it would be described as 50% efficient OR 85% coefficient of performance but NOT 85% efficient. Someone tell me if I am wrong here...
From my own experience, small wind turbines need about a 15 deg trailing edge flap to generate usable torque. Plan on a tip speed of 250-300kmh. If made of timber, an erosion strip is needed on the leading edge of the outer third of the blade. Use low density high strength timber like spruce or good clean sections of western red cedar. spin the turbine for several days before sealing it as any mobile moisture and resin will seep out through the timber end grain on the blade tips. Once the seepage stops the timber is fully cured and you can seal it up.
would it be fairly straight-forward to build a very simply numerical model of a turbine responding to a laminar flow? Might be fun to do a coding video with something like vpython or some other nice graphical tool.
Yes, but note its a theoretical limit not a real world achievable one. Also in practice HAWT get nearer that theoretical max than VAWT -- I have no idea why
VAWT have the problem of drag of the blade moving upwind. For this reason they are inherently less efficient than HAWT. However, VAWT can have some advantages in very flukey turbulent winds such as can occur around high rise buildings because an HAWT takes time to respond to sudden changes in wind direction.
windturbines are not efficient you told us in the other video.. because they are not allowed to turn so fast like they could... so how much efficient are they realy???
I was wondering how pressure dynamics work in this; i would think the stream of air would collapse a bit because the air that doesn't pass through A (surface blades) retains its pressure and is higher that the pressure of the output air going through A. but then i thought, since v(out) < v(in) ==> more air behind the blades, so increase in pressure? More generally, how are the wind turbines explained in terms of pressure?
Pressure in moving fluids ist more complicated than this. There is static pressure- the weight of the air column above squeezing the air down here to its density. But there is also dynamic pressure- the kinetic energy of the air having a speed higher than zero. The turbine extracts energy from dynamic pressure- decreasing dynamic pressure by slowing down the airflow. Static pressure stays nearly the same. (ignoring differences in ground heigth and air density that i hope are negligable in the scale of our hozizontal flow through the wind turbine) Also, this is the explanation why rather than collapse (having lost static pressure) , the air flow has to spread behind the turbine - to get the same mass of air moving away from the turbine, the slowed- down air has to flow in a larger total cross section than before. Keywords: venturi effect, bernoulli's equation
I would have thought it was to balance the power to each phase of the generator(assuming 3 phase AC generator). That way if there is different speed and mass of the air across the area of the blade rotation, then each phase would see the same torque pulsing with a three blade system. Since the generation produces an apposing force, unbalanced generation torque would put the blades seemingly out of balance. That's just the way my head works so I could be wrong.
So, an incredibly clever person who helped me understand something and didn't make me feel like an idiot, that's a rare gift.
There a rule for journalism which states; if a headline asks a question then the answer is no.
I liked how you put the ‘no’ in the thumbnail.
It's not only jounalism: note for example the hymn "Jerusalem" which is simply a series of questions all of which have the answer "no"
th-cam.com/video/IWwSdmSSv1k/w-d-xo.html
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So glad the algorithm showed me your channel!
Rosie,
I have just stumbled upon this video of yours and I'll come right out and say it.
It has tbe best thumbnail a video on TH-cam can have.
It poses a great question,
It gives the "Tldr" answer, and has your smiley face there so we all know its not more AI created bot content.
Love your work mate!
Hi, Rosie!
Just want you to know, this is the 3rd or 4th video I've watched from your channel, and all have been nothing short of phenomenal. Thank you so much for taking the time to share your wealth of information and knowledge. Keep up the good work - I'm looking forward for more!
... i find it very hard to explain things to people who aren't on the same level ...
You do such a wonderful job explaining complex problems so that i can understand them effortlessly .
Thx so much 👍🏼❤️🖖🏼
Would love to hear your thoughts on how gearboxes and generator shape and design affect turbine output.
The reduction gear and generator shape and size (unless stupidly large in diameter) has neglible impacto on the turbine rotors ability to extract power from the wind, however the design of the reduction gear and generator will have great impact on how much of the power extracted by the turbine rotor that can be turned into electrical power.
Gearless elevator machine efficiency ~90%
Geared worm/gear-ring elevator machine efficiency ~50%
Just from memory because I'm not digging out my notes from boxes (I'm a retired engineering consultant now specializing in sleeping & long walks). There's a formula for geared elevator machine efficiency though and it depends on the sheave diameter so the ~50% varies. Also, these are all worm/gear-ring machines and helical machines are more efficient (I never studied those because they're only used for winding-drum lifts). Electrical efficiency likely depends on the air gap because air has 5,000x the magnetic reluctance of soft iron. Big old D.C. motors had a huge 0.100" air gap. Small modern A.C. PM motors have tiny air gaps like maybe 0.003" but I don't really know exactly. An installer complained that problems with a new one were because the manufacturer told them 0.0005" less steel shim than required so the rotor was touching the stator pole faces, so obviously nothing like the old huge 0.100" air gap. I suppose generators are the same because electric motors and electric generators are the same thing, electric motors also generate electricity during "overhauling" (a situation where the load starts mechanically-pulling or electrically-pushing the electric motor round & round instead of the electric motor mechanically-pulling or electrically-pushing the load).
This is a trivial issue of power transmission.
Small wind turbines less than about 4m diameter dont need gearboxes because they rev fast enough (typically >200rpm) to use direct drive.
This channel is a great find!! Thank you for this!
From the comments I guess that over the last week or so the almighty algorithm has decided to push this channel very hard. I too belong to those people...
Simple but fantastic explanation! Thank you so much for this video!
Great lecture indeed.
Glad you think so!
I;'ve been for a couple decades trying/sometimes succeeding at building small wind turbines up to 24' diameter but usually smaller. Largely based on ideas and education from Hugh Piggot and others. These days I'm bombarded with questions and bad ideas/designs from folks on the internet. It'd be pretty neat if you could get Hugh on your show. I still build the occasional machine here in the US but only after carefully screening the potential client. Lo've your channel, you're doing it right.
Thanks for this comment! I would also like to have Hugh Piggot on the show, I haven't met him yet but I will try to get in touch.
@@EngineeringwithRosie he's a gem and a mentor for lots of folks in small wind.
If you manage to get him on the show let me know if you can, I would not want to miss it.
hi, i love the way you brief the whole concept ,its really very helpful. I'm research scholar from India working on the optimization of wind energy as part of my research work.so here i request you to pls give some ideas and technologies regarding to improve the power efficiency at lower wind speeds or variable wind speeds of wind turbines.
This was explained so well and very put together. Thank you for the hard work you put in in this video.
Nice vid on Betz! You say "stream tube" I say "cross section". The cross section is the area within the perimeter outline of the turbine as seen from the wind. Flanges, ducting etc, as you said are all part of this cross section (important, not "swept area" as that assumes horizontal perpendicular blades to the wind). In another video I believe (could be faulty memory) you mentioned that Betz didn't apply to vertical axis turbines? I'd be interested to understand your thought process behind that. To me, it's all the same. Cross section, energy in, energy removed, still needs energy to move the slower air mass away...Betz.
th-cam.com/video/IWwSdmSSv1k/w-d-xo.html
Very smart. Excellent video, you presented this material in a fun way. Thank you.
not piling up, but squattered to various directions with various velocities, therefore 100% is a limit, not 59% (due to simple pressure differences the air from other volumes would fill the area of stagnating air molecules)
Thank you very much. It was a great and interesting explanation
You look so happy in every video.
great stuff! Thanks
Glad you liked it!
Thankyou for the link to the derivation!
Using a microphone would take this already good video to the next level.
I have a better audio setup now 😊 Still working on improving every video. Check out my more recent ones and tell me if you think they're better.
Thanks. Now that wind turbines are appearing everywhere, it's about time that I gained some understanding of the mechanics.
th-cam.com/video/IWwSdmSSv1k/w-d-xo.html
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So easy to understand, and you seem to really enjoy presenting!
veeeeery nice vidoe! love it, thanks for sharing knowledge
Thanks! So nice of you.
Awesome! It seems crazy to me that you can extract as much as 59% of the energy when the blades only occupy a small fraction of the area of the rotor disk.
You need air flow. Block too much of the air flow and you decrease the velocity of the airstream passing by the blades reducing the kinetic energy available to be extracted.
I would love to see you work with numberphile in a video to explain the math of the bets limit!!
bets limit??
Thanks for your explanation. You're so happy!
The Betz Limit does apply to a circular disk actuator ( ie a HAWT ) . The stream tube passes through the blades only once. But in a H-Darrieus lift-type VAWT, the air stream can pass over the blades twice. I don't think, Betz ever considered that possibility. So, would a H-Darrieus VAWT be similar to placing a second HAWT, down-wind of the first HAWT? So, the second HAWT could ( at most ) extract another 59% of the remaining 59% energy, or another 35% (max) ? The combined energy could then exceed the "59% Limit" of the original air stream? Turbulence from the first HAWT would reduce the efficiency of second wind turbine, for sure. Also, a sail boat can "tack" into headwinds and it can travel faster than the incoming wind speed. What if 50% of the H-Darrieus blades that are moving into the head-winds, used this "sail boat tacking" method to extract energy? The H-Darrieus design is a 3-D Cylinder shape, not a 2-D circular disk actuator, therefore the Betz Formula may need a modification for H-Darrieus VAWT's, because of the assumptions made during the formula's derivation?
Thanks for this thoughtful question! You are right that the aerodynamic analysis is totally different for vertical axis turbines than it is for horizontal axis. But vertical axis turbines are less efficient, not more, than HAWTs. I am working on a video explaining the theory of VAWTs, but it will be a couple of months before it's ready. And I'll make sure to look back at your question and make sure I answer all the points you raise when I make that video.
One thing that is the same for VAWTs as HAWTs is that you cannot take all the energy out of the wind. There needs to be some velocity (and therefore energy) left in the wind so it can exit the rotor. But a more detailed answer is going to have to wait until the VAWT video, sorry about that!
@@EngineeringwithRosie Yes, I know that a W/T cannot extract 100% of the energy. I did write "... 59% of the energy is extracted ...". The Betz formula does not have any math for ... The wind tube entering the into the front-half of the VAWT, passing through middle of the rotor, and then the SAME wind tube exiting the rear-half of the VAWT. There are some very efficient H-Darrieus VAWT. Especially, the design with variable pitch blades ( up stream blade angle is different than the down stream blade angle ) by implementing a Wind Vane ( ie a tail ). The H-Darrieus can be made "directional" like a HAWT.
Thank you. Very informative.
Loved it ❤️
Thanks!
th-cam.com/video/IWwSdmSSv1k/w-d-xo.html
Murat was here. TFS (Thanks For Sharing)
Well-explained. Thanks a lot
Nice video, thanks
Can you do a video about solar updraft towers... there are a whole bunch of effects mixed together: stack effect of high speed air at altitude, heating/solar heating an air flow making it more energetic, the advantage of having the turbines near ground level (could be horizontal or vertical axis. Is it wind power (stack effect at the top?) is it solar? is it a combination?
Can you grow crops underneath? (since the airflow is always inbound from the outside, you can add humidity at the periphery, and potentially extract towards the centre.)
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I'm amazed to know that so much of research has already been done on maximum efficiency of wind turbine,,
But Rosie,, please answer me-why more number of blades are not used to enhance the efficiency?
I made a video on that 😀 th-cam.com/video/f3hgB-0rPOI/w-d-xo.html
@@EngineeringwithRosie okk,I will watch and then come back to you
@@EngineeringwithRosie sorry dear,, your video tells about twin blades,,but I'm asking about more than 3 blades,,
As I tell you,in car engines,,more number of cylinders will make engine smoother and vibration free,,3 cylinder engine is not considered a balance engine,,but 6 cylinder and more is balanced,,
So I'm planning to build a 6 or more blade vertical turbine,,or maybe a horizontal turbine with blades(6 or more) installed at 1 feet distance on the shaft,,with blade size 5 feet in dia,,
Do you approve this design?
The video also covers more than 3 blades.
@@EngineeringwithRosie I saw this video,,to me number of blades and their cost is not the big concern,,my ultimate goal is to get higher level of efficiency with compact and balanced design,,
So I want to know if 6 vertical blades of stainless steel will be good or not?
Excellent keep it up
Thanks a lot 😊
Hi Rosie, thank you for the explanation. Is the Betz limit also applicable for a darrieus type of rotor? These turbines touch the wind both on windward and leeward and are not really a disc from Betz perspective. What do you think?
Thank you very much!
Is the efficiency limit the same for water turbines (like in tidal power plants)? Do fact that air can be compressed matter?
That is a really interesting question! I am going to find a tidal energy expert to ask (could be a good 1 min video topic too). I suspect that yes it is the same, but I have never worked with tidal energy so I can't say for sure, maybe there is a factor I haven't considered. With aerodynamics, you usually assume incompressible flow below transonic speeds. And incompressible flow is usually assumed for wind turbine aerodynamic analysis. But as blades get longer and tip speeds increase, some researchers are starting to consider compressibility in the blade tip region.
th-cam.com/video/IWwSdmSSv1k/w-d-xo.html
Godd job ! ;)
Regards Paul P. ;)
Would be interesting to elaborate if any significant effects on moisture transport towards lee side of windfarms as well as on vetical upward displacement of air flow from slowing down the lower layer (acting as artificial hill). Can imagine this might have implications on thermodynamik of the local atmosphere (e.g. temperature profile)
th-cam.com/video/IWwSdmSSv1k/w-d-xo.html
Absolutely well explained (y)
Good videos! Keep up the good work.
Excellent and insightful video, once again. Couple comments: doesn't the shroud in your illustration show the opposite (diameter of stream tube hitting the blade being reduced), and the Venturi effect being used to impart a higher fluid velocity/energy to the turbine? Also, assuming it would be cost effective, wouldn't adding more blades extract more energy for the same swept area? Sure, you'd have to deal with the turbulence, but I cannot but think that the 3-blade design is letting a lot of the flow pass through between the blades without being used.
Hi, thanks for your comment! The streamtube is wider upstream with the shroud than it would be without it, which gives it a larger effective diameter than the rotor diameter, so it has access to more energy in that larger diameter. And yes, then the streamtube diameter decreases as it hits the rotor, and consequently speeds up. Probably worth more than the 2 second explanation I gave it here! Thanks for highlighting this, and I hope I can do a while video on shrouded turbines some time soon.
And on the question of how many blades/ how much of the rotor should be covered by blades to get maximum efficiency, that is another insightful question! I talk a bit about it in this video: th-cam.com/video/f3hgB-0rPOI/w-d-xo.html
And I will be talking a bit more about it in the next two videos in this series about how wind turbines work. But to be honest it is still probably not a really thorough explanation of why adding more blades doesn't increase energy capture. I have an idea of how I can demonstrate that, but it might take a few months to get it done in a way that is properly satisfying. Keep an eye out though!
@@EngineeringwithRosie It would be interesting to know how much of the available energy per area the blades are actually utilizing, unless it's already close enough to the Betz limit that 3 blades is a good compromise. But like you said in the video you linked, there's always room for improvements as well as compromise choices. Look forward to the new videos and thanks much for the reply.
@@slymartins yes it is pretty close already, about 80% of the Betz limit. And it wouldn't get better by simply adding a 4th blade to any modern 3 bladed turbine. I do plan to get more into why adding more blades (or making the blades wider) doesn't add more efficiency, but it will involve a bit of work to demonstrate it. So it will be some months away!
The quick explanation is that if you try to extract more energy by adding blades or making then wider than the optimum, you end up with each blade hitting the wake of the blade ahead of it.
@@EngineeringwithRosie Thanks much!
I'm convinced that the efficiency of wind turbines is far lower than its potential. If I were to design a boat that was powered by wind, I wouldn't use a small number of narrow (small surface area) sails. I would use as many as possible, and make them as large as possible, within reason. This current design appears to be the opposite, obviously. The blades are about as narrow as a toothpick (in terms of scale), and this is supposedly extracting nearly 50% of the energy? Maybe 50% of the energy of the air it comes into contact with, but not even close to 50% of the total energy available in the wind for that area. Most of the wind is not even touching the device. I would say, it appears >75% of the air flowing through the area is not impacting the blades at all. This cannot be the most efficient design. It needs to have sails. Otherwise, those old canvas windmills would have been designed in the same way, with tiny little blades, and no sails.
I was confused by this as well. I found these videos, which do a better job of explaining the relationship between number of blades, rotor velocity and efficiency: th-cam.com/video/BQI7AwKDQXk/w-d-xo.html th-cam.com/video/_dpGtOyma0Q/w-d-xo.html
I've also pondered this, there must be something we aren't understanding, I mean even with the airfoil effect it seem to not make sense.
@@somerandomnification The old dutch sail type wind mills were obviously sub-optimal, but that doesn't explain why the modern blades cover such a small area, look at the old "farm windmill" design, it's a lot more optimized and made tons of power to pump water in the old days, has anyone ever seen a direct comparison?
@@somerandomnification I'm not questioning the use of airfoils, I'm questioning the structure to power - (disclaimer, this is total speculation) if i were to build models of the new and antique design I'm pretty sure the antique design would out perform the new design, if I modified the antique design to only have 3 blades the new design would probably beat it, if I were to make another model of the new design with 6 blades it would have ~double the power output, does this not make sense? I realize turbulence could get in the way of the following blade but these designs aren't even close to that point.
@@somerandomnification Again, the efficiency of the design is not in question, we are talking about the power leveraged for the material used, for example - on paper hydrogen is the most efficient rocket fuel, but the larger structure required to use it made rockets that were more expensive then others, or how a sterling engine is more efficient then an internal combustion engine yet nobody would try to use it in a car as the amount of material needed to get the power required would be extreme.
How would it work for a configuration extracting not ALL/100% of the energy, but 95, 90 ?
Me: "I can make a wind turbine with 75% efficiency"
Rosie: "Betz".
Me: "ok , $100".
Rosie: facepalm
Can you clarify the orange vectors at 0:46? Are they drag forces?
Hello Rosie!
I like your explanation videos. Please go on. :-)
I am always astonished when magazines or newspapers report new developments with gigantic efficiencies. Very often they forgot wake effects, reduction of energy or the self consumption of systems. Why do they not have a look to the basics before they embarrass?
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The „disk“ simplification would be nice to be explained in more detail, what happens to those particles passing by the narrow blades…
th-cam.com/video/IWwSdmSSv1k/w-d-xo.html
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excellent explanation, what is the name of the software for modeling turbines that you showed? thank you, great job!
Curious that Rosie uses the term "stream tube" meaning intangible container of air, the physics of which have been altered by presence of turbine mounted directly in airstream. Why no mention of tangible stream tube, meaning ducting that captures wind, redirects, concentrates to turbine mounted on ground? Imagine a windy seashore (eg. Oregon, Washington coasts) with most wind coming from seaward. String a cable across top of valley, with fabric attached to trap onshore winds. Turbine can be fully enclosed, and running on air captured from entire valley section. Velocity depends on area-ratio of tube mouth to rotor circle.
Concepts like this have been tried. I saw one in Tasmania many years ago mounted on an ocean facing headland, a duct directed the windflow onto a multi blade turbine about seven metres in diameter. Not sure what happened to it but suspect issues of practicality defeated the idea. Multiple conventional three bladed power turbines are now at that location.
@@jimgraham6722 Well said. " issues of practicality" may include non-technical considerations, like politics.
Dear Rosie, can you upload the material.
4:13 here do you mean increasing or decreasing?
Brilliant Rosie and to a very non-technical person very well explained! Do you have any videos on solar panels and how to select the most appropriate please? Many thanks Regards Ian Inverness Scotland
I´s like a video on windpower for boats.
The Betz limit is true mostly for standard HAWTs. This "law" is not as strict as the law of conservation of energy and angular momentum, therefore it can be bypassed. I know the scientific community is very skeptical about such statements, but evidence of exceeding Betz’s limit with an efficiency close to 100% will be published soon. (Such as Francis water turbines with an efficiency above 95%)
Nice video; one question though.. You also mention modern turbine approach 50%. However, i'm a bit puzzeled; if i take a Siemens Gamesa 3,6MW offshore turbine, the rated windspeed is 12m/s. Yet, at this speed the theoretically available power in the 120m disc is roughly 12MW. Therefore, the turbine 'consumes' only say a third; far less then half.. Looking at other models, i see the same. Even the new GE Haliade; roughly a third. Yet all literature mentions commercial wind power nears the Betz limit. Or is this an averaged output used as typology and they actually put larger capacity generators in the nacelle. Can you explain this? Siemens Gamesa haven't replied on my email.. :)
Interesting question. I couldn't find the exact models you're talking about, but the ones I did find were not specifying their rated wind speed publicly. If the rated wind speed is 10m/s not 12 then the Siemens example you list works out roughly as expected. So I wonder if it's an issue with how the generator size and rated wind speed are selected/ communicated.
If you are exhausting into a vacuum, does it change the Betz limit?
The only variables in the equation are mass and velocity, Would either change? Mass won't, velocity may increase, but that does not increase efficiency.
@@gregripp I can't see the assumption made by looking at the equation. One assumption I predict they might have made is that the ambient air pressure is the same on both sides of the turbine since that would be true almost always.
Are wind turbines spaced such that the expanded "disk" of air exiting the turbines doesn't interfere? Or is there another factor for spacing between turbines?
Is it the same concept for vertical axis wind turbines?
Simple answer. When the turbine is in thermodynamic equilibrium with the wind, no more energy can be transferred. Beyond a certain point it would be pushing energy uphill.
What about the airflow which passes between the blades…is that not still at full energy as it leaves the disc? Would more blades not produce more power?
Which software do u use ?
I do have a design that is totally different from any known method of extracting electricity from wind power
Once I wipo it I will show you an amazing efficiency
Hi! What if these were made opposite? All wind turbines I’ve seen catch the air and make the blades spin in which generates power right? What if theres a turbine that instead catches the wind it it flows with it? Would this generate more wind? Would it act like a fan?
Did you come up with this question after seeing the latest Veritasium video? If not, then you need to see it, basically a physical manifestation of your questions!
I am still trying to get my head around how it works, I don't believe that the video gives the full explanation 😊 When I understand then I might make a video explaining how I think it works, and that would answer your questions too.
th-cam.com/video/jyQwgBAaBag/w-d-xo.html
Seems to me that's exactly a fan, and likewise an aircraft propeller...
so some other youtuber said that the energy expended to manufacture one wind turbine far exceeds the energy it would ever produce.... is that "horse feathrs" ?
Thanks for commenting! No that's not true. Wind turbines have one of the best energy payback periods of all techs. I will be making a video on the concept of EROI - energy return on investment soon (in a few months) where I can talk about it in depth.
@@EngineeringwithRosie Now all I have to do is decide who i believe.. A beautiful, highly intelligent ENGINEER or some youtube wannabe :)
gimme a sec.. i know the right answer.. :)
Does toroidal propeller exceed the Betz Limit?
4:19 I don't understand this, just looking at this clip it seems over 75% of the air will pass by unrestricted, how do they get close to 50% of the available energy? (edit: sorry, just went through the comments and saw 2 others already asked this question)
Have you covered SkySails Power in any videos?
A video on wings-on-ships is coming soon!
Just wondering since a wind turbine with 3 blades doesn’t cover the greater part of the wind stream how can maximum efficiency be achieved?
That is disk solidity and you could have 100% solidity with a single very wide blade like a screw. The rotational speed of low solidity turbines is high relative to the wind speed and a blade effects a volume of flow around it, so the effected air mass is still near 100% Maybe better to think about the diagonal path of the blades through the flow rather than a frontal view. This is a propeller vortex visible due to humidity but similar in principal th-cam.com/video/mk8b8Cv_0kk/w-d-xo.html pause it at 59 seconds note only a few inches of space.
I was confused by this as well. I found these videos, which do a better job of explaining the relationship between number of blades, rotor velocity and efficiency: th-cam.com/video/BQI7AwKDQXk/w-d-xo.html th-cam.com/video/_dpGtOyma0Q/w-d-xo.html
As an engineer, you ought to be able to design an audio setup that produces better quality, more intelligible sound for your video. I suggest you try
1) Move farther away from the hard, flat, echo-inducing wall
2) Move closer to the microphone, so it picks up more of your voice and less of the ambient sound of the room.
Thanks Rosie, Your explanations are clear and easy to follow. Can you recommend a small wind turbine for urban power generation, for a house with electric cars to charge, 1-2 kw? We live in an area where there can be a lot of wind but not steady, Juan da Fuca Strait on Vancouver Island. If you don't want to recommend a brand what to look for would be very helpful, and as quiet as possible to keep the neighbours happy.
th-cam.com/video/IWwSdmSSv1k/w-d-xo.html
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I use a Bergey XL1, these are excellent very rugged machines. Highly recommended.
Thanks Rosie.
I am an engineer and have been working on A VAWT design that works on the principles discussed in your video "VAWT Design". I have been working on this design for 10 years and have developed a computer model for a lift-based VAWT and have discovered several important concepts. I cannot find a mechanical engineering department in any universities here in the US that are working on this type of design. Do you know of any? By the way I think you left out an important variable in the equation you showed for aerodynamic force.
Thanks again.
Noel Potter
Hi Rosie. I have a concern: by using wind and wave power, we're extracting energy from the world's climate systems, and returning it later elsewhere as heat. Is it possible that this will contribute to the climate change crisis? I've never heard this possibility discussed.
afaik heat has neglicible(and temporary) effect on climate, the problem is greenhouse gasses acting as a blanket, sun heats up earth, blanket makes that less heat can escape, resulting in warmer climate
All the wind energy ends up as heat: if no windmill is present the wind slows eventually due to friction with the ground / mountains / etc
So ultimately no net effect
Will you please consider and compare the test results of a new kind of augmented vawt design of GMWT. GMWT ("G" Model Wind Turbine)
Hi Rosie - loved the vid, thanks. The 59% max Betz efficiency, that must be affected by the residual drag of the generator right? Is the efficiency calculated with or without the gen drag? I'm interested in your thoughts about that. Jerry
Was thinking the same. Weight/gearing of generator must surely come into play?
That's the theoretical efficiency of conversion from wind energy to rotor energy: with no other energy losses after the rotor.
You are both right that the real world efficiency will always be lower due to losses at every energy transfer all the way to the user...
Thank you for excellent video. I have small question, why the disk of wind is considered in 1/2 *rho*A*V^3, while only the 3 blade area is in contact with wind.?
Even the air between the blades is slowed down, without being in contact with the blades. Actually very few air particles get into contact with the blades.
Betz limit does assume the fluid is non-compressible, all fluids are compressible at some point even water.
From a very easy one like air, this theorem can't be applied
If you make a blade using the 1.618 golden ratio Diameter and gets bigger untill you Reach 21 or even 55 and Spiral it like Archimedes and make 12 of them you have the Perfect. Turbine to Capture almost 75%
Is wind turbine efficiency typically given as relative to the total energy in the stream tube, or relative to the Betz limit?
e.g. if a turbine could extract 50% of the wind energy, would it be called 50% or ~85% efficient?
If i understand correctly it would be described as 50% efficient OR 85% coefficient of performance but NOT 85% efficient.
Someone tell me if I am wrong here...
@@trueriver1950 thanks
I am thinking to make a wind turbine can you help me how to design it and aerodynamic design .
Absolutely! I have a whole playlist on wind turbine design, most of it to do with blade aerodynamics.
@@EngineeringwithRosie can you send it to me 😊😊
From my own experience, small wind turbines need about a 15 deg trailing edge flap to generate usable torque. Plan on a tip speed of 250-300kmh. If made of timber, an erosion strip is needed on the leading edge of the outer third of the blade. Use low density high strength timber like spruce or good clean sections of western red cedar. spin the turbine for several days before sealing it as any mobile moisture and resin will seep out through the timber end grain on the blade tips. Once the seepage stops the timber is fully cured and you can seal it up.
Good content, but you can definitely do with a better mic.
would it be fairly straight-forward to build a very simply numerical model of a turbine responding to a laminar flow? Might be fun to do a coding video with something like vpython or some other nice graphical tool.
Interesting explanation, I have always wondered what effect they have on the surrounding air mass since they are extracting energy.
Mass is not reduced only the velocity.
Does this apply to gas turbines?
Velocities, temperatures and pressures very much higher. A three bladed gas turbine wouldn't work
Did you say that in this use, the letter “e” is pronounced “row”? Why? I don’t know- third base!
That's a problem with my handwriting! It is the greek letter "rho" looks a bit like a "p" when written more neatly: ρ
does the same formula for efficiency apply to VAWT too?
Yes, but note its a theoretical limit not a real world achievable one.
Also in practice HAWT get nearer that theoretical max than VAWT -- I have no idea why
VAWT have the problem of drag of the blade moving upwind. For this reason they are inherently less efficient than HAWT.
However, VAWT can have some advantages in very flukey turbulent winds such as can occur around high rise buildings because an HAWT takes time to respond to sudden changes in wind direction.
Rosie please can you make a wind turbine
windturbines are not efficient you told us in the other video..
because they are not allowed to turn so fast like they could... so how much efficient are they realy???
Does it hurt the wind??😢😢😢😢😢😢❤
In what way are they a turbine? If they have a shroud then they are. That is not 'adding a shroud to a turbine' - it is turning it into a turbine.
Turbines do not require shrouds to be a turbine. A turbine is a spinning mechanism used to make power by using a fluid flow.
Build wind turbine. That can build them self. No crane needed.
Like building where crane use building as a base
The audio level is too low for me to listen comfortably...
I was wondering how pressure dynamics work in this; i would think the stream of air would collapse a bit because the air that doesn't pass through A (surface blades) retains its pressure and is higher that the pressure of the output air going through A. but then i thought, since v(out) < v(in) ==> more air behind the blades, so increase in pressure?
More generally, how are the wind turbines explained in terms of pressure?
Pressure in moving fluids ist more complicated than this. There is static pressure- the weight of the air column above squeezing the air down here to its density. But there is also dynamic pressure- the kinetic energy of the air having a speed higher than zero.
The turbine extracts energy from dynamic pressure- decreasing dynamic pressure by slowing down the airflow. Static pressure stays nearly the same. (ignoring differences in ground heigth and air density that i hope are negligable in the scale of our hozizontal flow through the wind turbine)
Also, this is the explanation why rather than collapse (having lost static pressure) , the air flow has to spread behind the turbine - to get the same mass of air moving away from the turbine, the slowed- down air has to flow in a larger total cross section than before.
Keywords: venturi effect, bernoulli's equation
heppolt wind
bend 90 degrees, impeller wind turbine
In other words, what you're saying is that when it comes to wind turbines, all Betz are off?.....
😂
She's only encouraging you for the engagement. That was terrible and if you have any decency you should isolate yourself from humanity.
@@Barnaclebeard 🤣 nope I am just a sucker for puns, even (especially) terrible ones!
I would have thought it was to balance the power to each phase of the generator(assuming 3 phase AC generator). That way if there is different speed and mass of the air across the area of the blade rotation, then each phase would see the same torque pulsing with a three blade system. Since the generation produces an apposing force, unbalanced generation torque would put the blades seemingly out of balance. That's just the way my head works so I could be wrong.
Air particles? How very Lagrangian of you. You may wish to look at Eulerian solutions which would be move valid at reasonable speeds.