Siemens 21MW prototype machine

[smegal]

Tip speeds of around 200mph seems to be the max on large wind turbines (3 blade) as they wear out to quickly over that.

Are you sure you don't mean m/s as opposed to mph?

I just did a sense check on a 14 MW turbine, 222m diameter, 12.7 rpm have 147 m/s or 328 mph.

[smegal]

.....
Prior to this monster I believe blade tips were approaching speeds of 550mph at max rpm. I wonder if the sound barrier will come into play at any point?

IIRC some of the very early 2 blade windmills did go supersonic, which causes some noise nuisance ( if your standing in the plane of the mill, such that the supersonic tips are travelling towards you then you hear that heavy "thud, thud, thud" as you do when a fast moving helicopter is coming towards you - for the same reason of course: the tip of the advancing blade of the helicopter is going supersonic)

My thought was that they design them to stay below the speed of sound (~750mph? It varies a bit) for that reason. But if they're only up to 550mph I think there's some headroom.

Keeping tip speeds subsonic is very important from a noise perspective. But faster rpm needs less gearing, so there's a tradeoff.

That said, many turbines are direct drive, so gearing isn't as much of an issue.

[nowty]

Tip speeds of around 200mph seems to be the max on large wind turbines (3 blade) as they wear out to quickly over that.

Are you sure you don't mean m/s as opposed to mph?

I just did a sense check on a 14 MW turbine, 222m diameter, 12.7 rpm have 147 m/s or 328 mph.

Have you got the datasheet link ?

I worked out Ripple GF 2.5MW turbine (100m diameter) was around 180mph at 15 RPM and I read somewhere about the 200 mph limit. But must admit I had difficulty finding empirical data for the really massive offshore beasts.

[smegal]

Interestingly, Vensys seem to be rigidly sticking to around 76 m/s.

The only information I found for the Siemens units was this:
https://en.wind-turbine-models.com/turb ... -14-222-dd

This is probably the most reliable source.

https://assets.publishing.service.gov.u ... of_NMC.pdf

This shows a turbine with a diameter of 220m having an RPM of 8.7, which gives a tip speed of 100 m/s (223 mph)

[sharpener]

Perhaps that is a motivating factor for the Direct Drive that Siemens are using.

I wonder if the blades could be made in 2 (or more) pieces and fitted togethr on site or even during the assembly phase

That said, many turbines are direct drive, so gearing isn't as much of an issue.

See also https://www.gevernova.com/wind-power/of ... de-150-6mw.

Good to see DD making a comeback, I imagine the falling cost of permanent magnets and rising cost of offshore maintenance will have tipped the balance. Having said which I read that Siemens have taken a big write-down recently.

The direct drive architecture was IIRC pioneered by Enercon, but was ahead of its time and the Danish model prevailed. Their double-fed induction generators only work over a 2:1 speed range and require slip-rings which give significant maintenance problems as does the gearbox. You need a complicated inverter either way (but for the DFIG it only needs to transmit 1/3 of the power, the rest comes straight off the stator windings).

[smegal]

Perhaps that is a motivating factor for the Direct Drive that Siemens are using.

I wonder if the blades could be made in 2 (or more) pieces and fitted togethr on site or even during the assembly phase

The blades all seem to be in one piece. I was thinking how they'd join them, I was thinking of an internally flanged arrangement like tower sections, or connecting the blade to the hub, but you'd need an operator inside the blade to tighten the nuts up.

I guess for offshore wind, there is less of an advantage to 2 part blades as you don't have to transport by road and you have tall cranes for lifting the nacelle anyway which is WAY heavier.

[sharpener]

Perhaps that is a motivating factor for the Direct Drive that Siemens are using.

I wonder if the blades could be made in 2 (or more) pieces and fitted togethr on site or even during the assembly phase

The blades all seem to be in one piece. I was thinking how they'd join them, I was thinking of an internally flanged arrangement like tower sections, or connecting the blade to the hub, but you'd need an operator inside the blade to tighten the nuts up.

I guess for offshore wind, there is less of an advantage to 2 part blades as you don't have to transport by road and you have tall cranes for lifting the nacelle anyway which is WAY heavier.

IIRC the transition from carbon or glass fibre to a flanged joint is very difficult to engineer well. If using T-bolts or ribbed "carrots" you need to cut away a lot of the fibres so you need a bigger o/d in that area to compensate. Doing this at the blade root is bad enough, I would not want to do it a second time part way up the blade. A sleeve type joint would be easier but be heavily reliant on the glue(!), I don't know what its fatigue life would be. Aerodynamics are very important so you cannot have fasteners (or anything at all) protruding from a smooth outline.

[Sunrisemike]

Actually, a local firm, Blade Dynamics, here in Cowes, did develop and build two part blades. They got taken over by an American firm and moved to Houston. Not sure if they continued with the development or not.

"Blade Dynamics is a UK-based company that developed a two-piece wind turbine blade design with a modular construction to reduce costs and increase output:
Design
The blade's modular design allows for assembly on-site, which reduces the need for transporting longer blades and the associated costs for permitting and road work. The blade tips can also be adjusted to meet the specific wind conditions and requirements of a site.
Manufacturing
The final stages of manufacturing can be completed near the installation or deployment site, which allows for manufacturing to be distributed across a country."