wind turbine wobble

[eastendeng]

I have a client with a 45' wind turbine on a residential property. It has had a high pitched hum that was bothering the homeowner and neighbors so the home owner installed acoustic foam on the tower in an effort to dampen the noise. While it did help quiet things down, the tower has started to sway in high (>12kts) winds. It's not at the point where it looks like one of those inflatable figures in front of car dealerships, however it does sway enough to create concern. My initial response is to remove the insulation, check the torque on the head/tower connection and see if that fixes the wobble. if so great, but then we still have to deal with the noise.
Any ideas?

 

[racookpe1978]

45 foot dia is a big one.

Wind turbines are a source of long-traveling, greatly irritating, low frequency (long distance) and mid-frequency (air and ground/tower) noise. The popular press, never ones to criticize their chosen few ideologies of "green power" refuse to admit and publish these irritations, but they are a real problem to the industry.

Good luck. If the tower frequencies are "evident" when the tower is lightly touched while operating at the critical (noisiest) wind speed and power level, then adding vertical ribs (stiffeners) inside or outside the tower will increase weight (moves the critical mass away from a esonnance frequency) and will add stiffness to reduce the physical movement (vibration) of the steel skin that produces noise and (future) fatigue failure. I'm surprised the light weight insulation foam helped.

If the problem is cell enclosure vibration and movement, adding some mass above the bearing ring in the enclosure will help. But this will increase drag on the yaw motor and yaw motor drive trains.

 

[eastendeng]

thanks for the reply. to clarify, the tower is 45' high, not the blade diameter (its a small residential turbine - can produce up to 60kwh/day if 20kts winds are steady). I would think the problem is still the same. I'm looking at if the modifications to the tower could have caused the wobble. the insulation is epoxied on so removing it will be a problem. I understand that a slightly larger diameter tower with thicker walls has helped reduce the noise issue however not eliminated it completely

 

[chicopee]

The tower allowable deflection should have been design with the acoustic foam in mind. Somehow the moment of inertia of the tower will need to be increased.

 

[BigInch]

I'd suggest that, if you don't want to remove the foam, you might want to look at trying "Von Karmen Vortex Breakers", provided that they can be installed without interfering with the blade swing. You might try alternating foam on one side of the tower, then the other(??).

RacookPE, The wind turbine industry doesn't exactly tell the media, or anybody else, anything about these noises and a few other "engineering secrets".

 

[btrueblood]

So...they glued foam on the outside of the skin? That would have a definite impact on the drag forces that the tower generates, due to increased cross-section area, and could also lower the fundamental frequency of vortices generated (see Strouhal number entry in wikipedia). BigInch has a good idea.