'Nacelle Tilt angle'

[Usman]

I would like to know which is the most 'aerodynamically efficient' horizontal tilt angle of mounting for the nacelle (horizontally) or the rotor with respect to the tower for upwind machines.

The reason I mentioned aerodynamically efficient because some turbine manufacture choose a certain angle to lean the rotor away from the tower to avoid strikes especially where the rotor is too close to the tower. For others, that may not pose a problem and they could go for the most efficient angle.

A few turbine manufacturers that I have spoken to say that 7 degrees inclination w.r.t the ground level is the most efficient one, since if it was 0 degrees, the rotor would be perfectly parallel to the tower and that may pose some turbulence in medium to high winds.

While a few others manufacturers consider that just an excuse to steer attention from a bad turbine design where the tip of the lower passing blades tends to be too close to pose a striking risk. In fact, any thing more than 0 degrees would tend to loose efficiency. That's a reason why some designs furl upwards in high winds to decrease efficiency and rpm.  

I would like to get opinion from the community on the most efficient angle of inclination in their opinion.

Thanks.

[SparWeb]

Well, any time you point the rotor away from the direction of the wind, you collect a bit less power from it.

In a manner of speaking, you are just reducing the "efficiency", the more you tilt away from the tower.

Nothing about tilting the rotor up will make it more efficient, so none of the people you are talking to are giving you the straight story.

When the windmill is collecting power, there is a thrust load that bends the blades back, toward the tower.  Then, in a wind gust, the rotor yaws around into the changing wind direction.  The gyroscopic forces also bend the blades, and at times that can be directed toward the tower, too.  Add the two displacements, plus a safety margin, and you get a measure of how far the blades must be from the tower to not hit it.

If mounting the mill horizontally puts the blades in the danger zone, then it must be tilted.  Or shifted forward.  The "most efficient" angle is the one that gets the blade tip out of the danger zone.

By the way, tilting a rotor disk 7 degrees out of the wind direction reduces the power it can collect by 0.75%.  No big deal.

[Flux]

I kept out of this as it seems a case of theory overriding common sense. I am sure the angle varies from site to site and if the thing is on the top of a hill then the best power capture may come from having it tilted slightly downwards.

Real wind is not much like the theoretical stuff and almost certainly will be a series of vortices and who knows where the ideal direction to point it is.

Forget the stupid theory, if safe keep it horizontal, if there is a danger of tower strike then tip it up at an angle. What about the horizontal direction, are you happy to have a tail and let it yaw or are you going to position it at some calculated direction with a servo, whatever you do it will never be ideal. Perhaps you need a modified tail to let it yaw up and down as well.

Flux

[Usman]

Hi,

Thanks for your input. WHats the difference in between the cone angle and the tilt angle?

Thanks.