Wind Turbine Wall

[mistermack]

6 hours ago, studiot said:

Yes, but you can shield against this effect, which you would need to do anyway as you do not want the rotor to be driven backwards in certain winds.

Well you could, but it would be a complicated system, to move the shield around as the wind direction changes. And it wouldn't be suitable for this wall, which would only work at it's best with a wind at 90 degrees to it. Fixed shielding would detract as the wind veered around.

 

6 hours ago, studiot said:

why have you not taken on board what I have said several times about diameter ?

Well you mentioned diameter but didn't make any specific point about it. I'm assuming that you mean that the swept area increases with the square of the radius, making size increases more attractive on the traditional HAWT design? That's a fact, but size increases come with greater stresses, putting bigger demands on materials. Of course, bigger size takes you further away from the ground, giving access to stronger and more reliable wind, so that's another factor in favour of diameter increase.

The actual vanes mechanism on this wall are not gone into in detail, but look to be the basic drag type two scoop Savonius style design, which is one of the least efficient early types of turbine. Another reason that manufacturers wouldn't be impressed.

[studiot]

2 hours ago, mistermack said:

Well you could, but it would be a complicated system, to move the shield around as the wind direction changes. And it wouldn't be suitable for this wall, which would only work at it's best with a wind at 90 degrees to it. Fixed shielding would detract as the wind veered around.

 

Well you mentioned diameter but didn't make any specific point about it. I'm assuming that you mean that the swept area increases with the square of the radius, making size increases more attractive on the traditional HAWT design? That's a fact, but size increases come with greater stresses, putting bigger demands on materials. Of course, bigger size takes you further away from the ground, giving access to stronger and more reliable wind, so that's another factor in favour of diameter increase.

The actual vanes mechanism on this wall are not gone into in detail, but look to be the basic drag type two scoop Savonius style design, which is one of the least efficient early types of turbine. Another reason that manufacturers wouldn't be impressed.

Quote

notshakespeare

Methinks the gentleman assumes too much.

A shield can be as simple as a fixed deflector plate.

I mentioned at least twice that it is structural support considerations that limit the size of vertical axis rotors.
Perhaps you should follow the new thread on bending moments in Homework Help.

Edited October 27, 2021 by studiot

[mistermack]

2 hours ago, studiot said:

A shield can be as simple as a fixed deflector plate.

Can be, but it then wouldn't adjust to different wind direction. And in any case, the deflection would interfere with the flow elsewhere. And you still have the problem of air being forced into the path of the oncoming flow by the returning vane. 

There are design possibilities to get around some of these problems that are being explored. Quote wiki :

"Dulas, Anglesey received permission in March 2014 to install a prototype VAWT on the breakwater at Port Talbot waterside. The turbine is a new design, supplied by Wales-based C-FEC (Swansea),^[24] and will be operated for a two-year trial.^[25] This VAWT incorporates a wind shield which blocks the wind from the advancing blades, and thus requires a wind-direction sensor and a positioning mechanism, as opposed to the "egg-beater" types of VAWTs discussed above.^[24]"   

2 hours ago, studiot said:

I mentioned at least twice that it is structural support considerations that limit the size of vertical axis rotors.

No you didn't.                                

[studiot]

21 minutes ago, mistermack said:

No you didn't.     

 

I believe I did.

 

12 hours ago, studiot said:

I gave you the Physics, what problem do you have with it and why have you not taken on board what I have said several times about diameter ?

22 hours ago, studiot said:

The main reason for the lower efficiency of vertical axis machines is that the diameter that can be supported is limited substantially compared to horizontal axis machines.

[mistermack]

Yeh but that's not what you said. I find those posts rather vague, you throw in the word diameter but don't get to the point of why it is a problem. And then complain that I didn't respond. It's because you weren't specific about what the problem was that I didn't respond to it. 

In any case, I've seen some very big examples of vertical axis  turbines, so I don't think the diameter is as restricting as you claim. They are being deployed here and there, but they need quite a bit of engineering to get around the inherent problems. But that's not to say it can't be done. 

But this example, of 25 tightly packed in a wall, looks to be a non starter, for the reasons's I've posted earlier. That's just my opinion, and I've posted my reasons, for others to disagree with as they wish. 

[J.C.MacSwell]

On 10/25/2021 at 3:26 PM, exchemist said:

20mph is quite a strong breeze, for a city house. 10mph would be a more realistic average, I should have thought, judging by the daily wind speeds in London weather forecasts at least. Which presumably reduces the power by a factor of 4. 

8 actually.

[J.C.MacSwell]

On 10/26/2021 at 8:52 AM, studiot said:

Perhaps you should revise your aerodynamic theory ?

With laminar flow there is no interference between the units.

A lot of smaller units have the advantage over one big one in the event of a unit breaking down / needing servicing electricity supply is hardly interrupted.

One big one is an 'all your eggs in one basket' situation.

 

 

First of all this type of rotor is a high drag device with lots of turbulence. Second, even the most aerodynamically efficient units interfere with each other when in close proximity, even when not in each others "dirty air".

[joigus]

6 hours ago, J.C.MacSwell said:

First of all this type of rotor is a high drag device with lots of turbulence.

This is kind of the argument I was thinking about. Wouldn't that wall have lots of turbulence, with the rotors somehow working against each other? I would like to hear more about this.

[J.C.MacSwell]

18 hours ago, joigus said:

This is kind of the argument I was thinking about. Wouldn't that wall have lots of turbulence, with the rotors somehow working against each other? I would like to hear more about this.

Before even considering turbulence, if you consider what the Betz's limit is based on, limitations of how much energy can be removed based on the swept area:

Consider that for an array of rotors it's not just swept areas A that cannot overlap, but the A2s also...any closer and they are choking each other from lack area for air removal.

In practice even that close together cannot be approached, and of course as Mistermack has mentioned if the wind is anything but at 90 degrees to the array (wall) the interference gets higher.

 

The swept area of the rotors in the wall are squares, not discs, but the same principles apply...and as also has been mentioned these rotors are much less aerodynamically efficient than standard horizontal axis turbines. Note also that the standard turbines have 2 or 3 blades, not more, for similar reasons. Try to take too much energy out and you get less.

[studiot]

2 hours ago, J.C.MacSwell said:

Before even considering turbulence, if you consider what the Betz's limit is based on, limitations of how much energy can be removed based on the swept area:

The rotors in the article picture are nothing like your diagram.

I note that the rotors in the picture do not vent into clear air.

 

 

Interestingly I had a detailed discussion about the idea with a gas dynamics engineer.

He offered the following points.

1.  He agreed that the there is an issue with the structural design of having most of the weight at the tip of the rotor in vertical axis turbines.
   However he pointed out that this could be overcome with more machinery ie a low friction support track at the edges.
   He also agreed that this would be impractical in marine situations where you can't support the track on water.
    
2. He also said that vertical axis turbines of the sort described have a problem starting and are prone to stopping particularly when the incident wind is not in the best drection.
   He said that conventional vertical arrays (yes apparently they have been studied from an engineering point of view) are designed with a helical set to the blade direction to offset this issue.
   Reverse Axial flow impellors are also possible.

 

[J.C.MacSwell]

21 minutes ago, studiot said:

The rotors in the article picture are nothing like your diagram.

3 hours ago, J.C.MacSwell said:

The swept area of the rotors in the wall are squares, not discs, but the same principles apply...

 

Is that not apparent?

Edited October 31, 2021 by J.C.MacSwell

[studiot]

12 minutes ago, J.C.MacSwell said:

Is that not apparent?

It's apparent you omitted to read the second line.

33 minutes ago, studiot said:

I note that the rotors in the picture do not vent into clear air.

 

[J.C.MacSwell]

That exacerbates the problems further. Detrimental effects due to congestion of the rotors themselves still apply.

Edited October 31, 2021 by J.C.MacSwell

[studiot]

31 minutes ago, J.C.MacSwell said:

That exacerbates the problems further. Detrimental effects due to congestion still apply.

Not at all it simply makes a nonsense of any pretty diagrams showing streamtubes.

It is pretty obvious that

1) I can't have one (or more) of those big offshore type turbines in my garden as it is a normal subarban one.

2) If I lived an Exmoor and had the space for one, (there are some) placing it directly infornt of a wall or rock facce would enconter the same problems.
In fact a horizontal axis turbine might actually be more efficient.

 

But I thought the purpose of this thread was to discuss and dispassionately evaluate the worth and practically of the idea, not to destroy it with a negative agenda.

[mistermack]

1 hour ago, studiot said:

But I thought the purpose of this thread was to discuss and dispassionately evaluate the worth and practically of the idea, not to destroy it with a negative agenda.

Who's got an agenda? I would love to see a useful new idea and give it the thumbs up. But you have to call it as you see it. Apart from the problems of efficiency, this doesn't really have anything new that the proponent could patent. Even mounting them in a row has been tried, according to one of your posts. 

Small scale wind generation doesn't seem to attract small scale investment so far. Even though there are lots of small-scale solar installations. (possibly influenced by the grants that were available). 

I only know of two small scale units that I've seen on my travels. One was a very small HAWT in a back yard, which was there for a few years, but has disappeared, and the other was mounted on a narrowboat, which seemed to be a good idea. However, for a small turbine, it does make a heck of a noise when the wind blows. Maybe because small units give intrinsically low torque, they have to spin very fast to give a useful output.

[studiot]

3 hours ago, mistermack said:

Who's got an agenda? I would love to see a useful new idea and give it the thumbs up. But you have to call it as you see it. Apart from the problems of efficiency, this doesn't really have anything new that the proponent could patent. Even mounting them in a row has been tried, according to one of your posts. 

Small scale wind generation doesn't seem to attract small scale investment so far. Even though there are lots of small-scale solar installations. (possibly influenced by the grants that were available). 

I only know of two small scale units that I've seen on my travels. One was a very small HAWT in a back yard, which was there for a few years, but has disappeared, and the other was mounted on a narrowboat, which seemed to be a good idea. However, for a small turbine, it does make a heck of a noise when the wind blows. Maybe because small units give intrinsically low torque, they have to spin very fast to give a useful output.

Agenda  ? I didn't mention anyone specific, but are you feeling guilty ?

 

Smallscale wind generation ( a good termthank you I will adopt it), has been arounf for decades.

Not only on narrowboats, you only have to visit any marina to see many of these on boats trickle charging vital onboard electronic equipment.

Also visit umpteen highway locations, especially remote ones.
All manner of electronic highway equiment is being supplied from smallscale wind generators.
 

Wind generators have the advantage over solar in that the wind blows at night as well as in the day, unlike the sunshine.

In the UK it blows approximately 75% of the time.

Compare this to say 80% sunshine available 50% of the time.  (Do you get 80% sunshine where you live ?)

Now these small generators would not power the big motorway display boards.

But conceivably one of those walls would .

The point being that to scale up the conventional propellor driven generator would place an enormous risk of extreme damage/loss of life, if it failed and spun off into the traffic.

A suitable wall would not pose such a risk and could be sited and oriented so that MacSwell's flow problems did not exist.

So what if it was a bit less efficient ?

The biggest problem with such equipment I can see is thievery by antisocial members of the public who also don't care about environmental protection.

[exchemist]

On 10/30/2021 at 1:58 AM, J.C.MacSwell said:

8 actually.

Thats interesting. Is it the cube? I had assumed (without thinking much about it) a square relation, based on the ke in the wind. How does a cubic relation arise? 

[J.C.MacSwell]

2 hours ago, exchemist said:

Thats interesting. Is it the cube? I had assumed (without thinking much about it) a square relation, based on the ke in the wind. How does a cubic relation arise? 

4 times the energy per volume of air, but the flow is double, so as you suggest it's a cube relation.

4 hours ago, studiot said:

Agenda  ? I didn't mention anyone specific, but are you feeling guilty ?

 

I assumed that was directed at me, as you were quoting me in that post. If I sounded negative I apologize for the way I stated it.(not that I feel guilty as that was not my intent).

4 hours ago, studiot said:

 

A suitable wall would not pose such a risk and could be sited and oriented so that MacSwell's flow problems did not exist.

 

Unfortunately orientation doesn't change the limitations of that particular aspect of the problem/challenge.

You need room for the harvested air to exit the vicinity. 

Edited October 31, 2021 by J.C.MacSwell

[J.C.MacSwell]

If it doesn't exit you cannot harvest any more flow. The trade off is the basis of the Betz limit, and there are similarly further limits on how close you can effectively place rotors of any kind.

Edited October 31, 2021 by J.C.MacSwell

[studiot]

1 hour ago, J.C.MacSwell said:

I assumed that was directed at me, as you were quoting me in that post. If I sounded negative I apologize for the way I stated it.(not that I feel guilty as that was not my intent).

But I didn't quote you.

And my reply included a quote from another member with specific words I replied to and repeated in my reply.

But now you come to mention it.

Do you have an agenda ?

I am trying to evaluate where something based on the original idea might be usefully deployed.

You, on the other hand, appear to be exclusively bent on finding odd parts of my posts to quibble with (without reading them properly I might add).

 

1 hour ago, J.C.MacSwell said:

Unfortunately orientation doesn't change the limitations of that particular aspect of the problem/challenge.

You need room for the harvested air to exit the vicinity. 

 

51 minutes ago, J.C.MacSwell said:

If it doesn't exit you cannot harvest any more flow. The trade off is the basis of the Betz limit, and there are similarly further limits on how close you can effectively place rotors of any kind.

 

Are you seriously claiming that there is no room in Canada for the outflow?

Even in the much more densely populated UK I can find such places exactly where I proposed them.

Have you never seen a british motorway ?

I can assure you there is plenty of scope there to mount the type of vertical access rotors proposed for ships.
These are totally independent of wind direction.

And before you start wrongly accusing me of thinking of things I am not, here is a picture of flettner rotors driving a large ship.
Perhaps there is not enough room for the outflow air in the middel of the Atlantic ocean ???

 

 

Edited October 31, 2021 by studiot

[J.C.MacSwell]

3 minutes ago, studiot said:

But I didn't quote you.

And my reply included a quote from another member with specific words I replied to and repeated in my reply.

But now you come to mention it.

Do you have an agenda ?

I am trying to evaluate where something based on the original idea might be usefully deployed.

You, on the other hand, appear to be exclusively bent on finding odd parts of my posts to quibble with (without reading them properly I might add).

 

 

 

Are you seriously claiming that there is no room in Canada for the outflow?

Even in the much more densely populated UK I can find such places exactly where I proposed them.

Have you never seen a british motorway ?

I can assure you there is plenty of scope there to mount the type of vertical access rotors proposed for ships.
These are totally independent of wind direction.

And before you start wrongly accusing me of thinking of things I am not, here is a picture of flettner rotors driving a large ship.
Perhaps there is not enough room for the outflow air in the middel of the Atlantic ocean ???

 

 

Studiot I'm sorry you fail to understand my posts. Maybe someone can explain the concept better, but there is only so much room in close proximity to where you are harnessing the energy of the wind.

Flettner rotors are a pretty inefficient way of creating a poorly shaped airfoil.

[studiot]

2 minutes ago, J.C.MacSwell said:

Studiot I'm sorry you fail to understand my posts. Maybe someone can explain the concept better, but there is only so much room in close proximity to where you are harnessing the energy of the wind

How can I understand if you don't address my points ?

What do you know about my motorway proposal  and why do you keep refuting it ?

Edited October 31, 2021 by studiot

[J.C.MacSwell]

5 minutes ago, studiot said:

How can I understand if you don't address my points ?

What do you know about my motorway proposal  and why do you keep refuting it ?

I am unaware you had a motorway proposal and made no attempt to refute it.

Does it have anything to do with this topic?

Something to do with Flettner rotors? I'm honestly at a total loss here. What are you on about?

[mistermack]

Those rotors are not driven by the wind. They are driven by the exhaust gases of nine giant marine diesel generators, via a steam turbine. They are not vertical axis wind turbines by any stretch of the imagination. 

What they do is provide a forward thrust, like a sailing ship. Nothing wrong with that but it's not really relevant to wind turbine generators. 

[J.C.MacSwell]

19 minutes ago, mistermack said:

Those rotors are not driven by the wind. They are driven by the exhaust gases of nine giant marine diesel generators, via a steam turbine. They are not vertical axis wind turbines by any stretch of the imagination. 

What they do is provide a forward thrust, like a sailing ship. Nothing wrong with that but it's not really relevant to wind turbine generators. 

They spin an upright cylinder such that the boundary layer essentially creates a very inefficient airfoil shape. You don't need waste energy to do that...just put up a (hopefully more effectively shaped) sail.

Any thrust does in fact come from the wind.

In no wind Flettner rotors create no thrust.

(note that there is little if any wind in your photo of the "Flettner rotors driving a large ship", which probably explains why the lines to this anchored ship are slack)

Edited November 1, 2021 by J.C.MacSwell