HP Windturbine in Berlin City-Park -- small vibration problems on tale vane

[Hans Peter Duesentrieb]

hello everybody,

my name is immanuel, i´m part of an association (named kitrad) which runs an 700W-HP-Windturbine in a park in berlin.
it is a 2,4 m diametre, neodym-magnet wind turbine.

we have some minor vibration-problems on the tale vane. because the wind turbine is located in a public place which in summer is really crowded our primary goal is to run the turbine as safe as possible!!!

first we thought the vibrations come from an unbalanced rotor but we already took the turbine down and double-checked the balancing. and it looked ok.

our second idea of the origin of the vibrations is now the shape of the vane. as shown in the picture below the upper left corner sticks out quite a bit without any metal support. so we think the vibrations are just aerodynamic-induced vibrations on the tale vane.


yesterday we tryed to build a new vane with a more conservative shape-approach (as seen in the picture below).
.

here comes my main question:
somehow we don´t manage to get the demanded measurements of approx. 50 x 120 cm and the weight with the demandet weight of 1,8 kg.
we currently have 50 x 116 cm with 2,5 kg.

our main goal is it to have a safe running turbine in the park, so everybody can enjoy it.
so what are the design-driving screws here? is it better to get the right weight with quite a different area or otherway around?

I already read here that the weight is more less a linear function of the furling behaviour.

but since experience is much more worth then reading things i would like to ask you what your suggestions would be?

I´m greatful for any helpful suggestion, comment or idea.

with best regards from berlin
immanuel

[Hugh Piggott]

hi Immanuel,

If the vibration is slow then it is probably driven by the blades and maybe you can balance them better. If it is fast (more like a growl) then it is unbalanced electrical load such as a broken wire or failed diode.

If you want to make the tail smaller then that's OK but you will get less energy.  Maybe safety is more important?  To be honest I think this is about the perception of safety but it's still important.

My goal with tail design is to make the moment of area as large as possible while achieving the correct moment of weight.  Sometimes this means that the plywood is rather thin and it wobbles.  If the blades are well balanced then this should not happen.  But if it is a problem then you can make the moment of area smaller and you will only lose a little energy as the turbine will not face the wind so well.  You can for example use a smaller piece of thicker plywood to achieve the same moment of weight.  Hopefully this will not vibrate and the problem will be solved.

I hope this helps.

Hugh

[Hans Peter Duesentrieb]

Hello Hugh,

thank you very much for your advise and please excuse the very late answer/-:
we have finally changed the tail to a thicker plywood. therefore the area became a bit smaller.
it still vibrates a liddle bit but looks much better then the old tailvane with one outstanding edge.

we decided to rather have a less energy and have a save and smooth running turbine due to the public location of the turbine.
we also balanced the blades again and checked all electric parts. now everything looks good(-:

thanks again and best regards from berlin
immanuel