Wind Turbines

LOL

More blades do not mean more power! The maximum power available is set by the wind speed (of course!) and by the area swept by the turbine blades - the "disc area" in turbomachinery parlance. Two blades or twenty, that limit, as calculated by Betz, is roughly half the kinetic power of the air that would go through the disc if the turbine were not present.

For power generation, best efficiency is achieved (that is, the output comes closest to the Betz limit) if the blades turn quickly, so the typical wind turbine design is two or three narrow blades turning at high rpm. Three blades have mechanical advantages and are easier to dynamically balance, so that is the most common arrangement for horizontal-axis wind turbines.

Another reason,

The turning blade creates turbulent air behind it and the air needs time to recover. too many blades, and the blades will turn into disturbed air and the laminar flow over the blade will be less efficient causing the blade to sometimes spin even slower. slower RPM means less power.

It is similar to an airplane flying into turbulent air.

Wangito.

Yes. this is the same question that I would like to have asked.

Why, are there 10 thousand blades on a steam turbine or a jet engine. Yes I also exaggerate.

'n yes I can understand the enthalpy of steam on blades and etc...etc....

Here in Australia, we have a multitude of Windmills, all with multiple blades.

Somewhere, In the game of model aeroplane ducted fans, I remember "Blade solidity" that gives better propulsion. Why then , the reciprocal, doesn't it work the other way.

Is it about the losses of gearing to acquire the speeds at the "END" that is the problem.

Me, lots of blades, means lots of power............

Also, there is peripheral speed, tip speed, which needs to be taken into account, it all seems a CROCK to me, 3 blades. But when it appears to be be Bullshit, sometimes it 'aint.

But then again the King, also looked lovely in his new clothes.

Love to know and understand it better,

Cheers Mark N.

This is from one of the cited sources, Wikipedia:

"Wind turbines developed over the last 50 years have almost universally used either two or three blades. Aerodynamic efficiency increases with number of blades but with diminishing return. Increasing the number of blades from one to two yields a six percent increase in aerodynamic efficiency, whereas increasing the blade count from two to three yields only an additional three percent in efficiency. Further increasing the blade count yields minimal improvements in aerodynamic efficiency and sacrifices too much in blade stiffness as the blades become thinner."

Lyn and others above have mostly covered this, but the difference in driving a propeller or blades acting inside a duct are a lot different to operating at low velocity in free air.

That low velocity means the closer the blades, the more the next blade is interfered with by the wake of the preceding one.

This interference the same reason you will seldom see more than 5 blades on an aircraft propeller.

Ideally a wind turbine would have 1 blade. Naturally it's been tried and found 'scientific experiment'.

The first practical option is 2 blades, but because (like 2 bladed helicopters) pitch 'twist' on the same longitudinal axis, the assembly is aerodynamically dynamically unstable.

It's a bit like when you drop a long strip of thin wood, or cardboard, it tumbles, rather than floats to the ground nicely flat. "Bull-roarer" is the Aboriginal application.

In a turbine, where the wind velocity is lower closer to the ground, the top blade 'flattens pitch, the bottom blade 'digs-in' into slower air and the rotor plane tilts, gyroscopic precession then causes a 'weaving' path, and the thing tends to go out of control, and massive stresses result.

So like a copter, 2 bladed turbines need/have a 'teeter hinge', and so require the complexity of a 'collective pitch system', if variable pitch is necessary - like larger turbines need.

The third blade 'removes' the single longitudinal axis and so the need for a teeter hinge. This also makes variable pitch a lot simpler.

No teeter is also desirable in terms of 'not weaving' as in not tower hitting.

So with 3, the cantilever of the nacelle/rotor is reduced, reducing the stresses in the slew assembly, so materials and weight.

Next; Tip speed.

If you regard the blade as driving the tip, the tip loss is obviously power not going into the generator.

At about 70m/s, (relative velocity) tip drag starts to exceed lift, i.e. the tip costs more power than it's providing. Hence bigger turbines turn slower.

Were it a propeller - you just HP it up to Mach 0.9 and the 'barrier' acts as a bounding duct. Whole different bag of rats.

Wind will just go around too much 'solidity'. Which is why Mr Betz, after a life time of work threw up his arms and uttered "you's will never get more than 59% out of this pesky free air stuff" OWTTE.

Currently, the commercial application of wind energy harnessing is primarily if not exclusively, horizontal-axis wind turbines even though vertical-axis wind turbines avoid most of the disadvantages inherent in the horizontal-axis design. For example, vertical-axis wind turbines are omni-directional and have a lower cut-in wind speed and higher cut-out speed, thus making the window of operation wider. Also, vertical-axis wind turbines have components that need servicing located at the bottom end of the structure making access more convenient. Vertical-axis wind turbines also allow for lower ratio gearboxes, which are less expensive and more efficient than gearboxes needed to operate horizontal-axis wind turbines. Further, vertical axis wind turbines are able to operate at higher wind speed and at lower risk of suffering wind damage. Finally, vertical-axis wind turbines adapt to a simpler design and construction… Thus, my present invention is the Square Rigged Sail Wind Turbine.

Best regards,

Jon Howard

henergyinnovations@gmail.com

Reading this thread the other day, it made me wonder why the axis wasn't vertical. After all, a wind speed indicator at a weather station is vertical axis, with the cups spinning around.

But then I wonder about the efficiency. The cups (or sail) are pushing against the wind during a portion of their rotation. It seems that the surface of the sail would need to rotate 90° in order to be able to cut through the wind and then rotate to vertical again when the main axis comes around again. That sounds like a lot of wear and somewhat complicated gearing, but could be possible I suppose. It's all about efficiency ratings in the end. I'm sure I'm not the first to consider this. So I wonder what the conventional arguments against it are.

Another possibility is while the wind is pushing the sail, the sail could be pushing against a frame. But when it passes the 180° point, the sail rotates on a vertical shaft on the outermost edge of the frame and stays parallel to the wind until it rotates another 180.

Again, I guess it's all about efficiency numbers, and comparing it to normal horizontal axis units.

Yep. Precisely what I was envisioning. But my thoughts hadn't evolved to multi-levels yet.

You drew that pretty fast!

Go here read this

Crucial part

"I suggest you research and come to understand 'lift' - and then study the lift vector diagrams of say a Darius turbine."

The full comment touches on your general questions to date.

Note how nice I was.

But IF SRSWT is determined to "trumpet" this 'concept', on any or every thread on wind, he/she invites the 'total, merciless comprehensive dismantling' of this Physics Heretical and Mechanics inept .... 'competition entry'.

Well sure. This is too simple to have been a unique idea. If it worked, it would already be in service.

And being nice on CR4 is always a good thing

We're all inventors, of a sort.

Help yourself to one doggy treat. Or a cigar.

Now... let me tell you about this perpetual motion machine I'm thinkin about....

I take it that the intent of science is to ease human existence. If you give way to coercion, science can be crippled, and your new machines may simply suggest new drudgeries. Should you then, in time discover all there is to be discovered, your progress must become a progress away from the bulk of humanity.

Galileo: ...

You are indeed living in the past - both technically and "quoterly'"

No technical riposte.

Just cry 'victim'.

What?: Are you seriously attempting to tar me as a 'Flat World Papist'?

Why don't you sit down, learn, then apply the basic physics.

Yep - it's a semi-giant anemometer with additional external frame turbulence losses.

Perhaps next time quote Theodore von Kármán?

_{But by all means, 'keep pushing'}

Hello, well I must admit these drawings are several years old. They are all shown in an other engineering section of CR4.

Best regards,

Jon