Darrieus engineering project

[nemorocksharder]

     Hi everyone, first post on here but I like a lot of what I've been reading so far,
I am building a darrieus wind turbine for a second year engineering project, it will be bolted to
a sailing boat's deck and the small power prduced will trickle charge the onboard batteries to drive
the motor when necessary. I have to complete it
by the end of the term and for a while I have been looking at different designs to see what will
be the most efficient, but what with time constraints and the fact this is mainly a course to
determine you ability to manage your own project I have just decided to go with a two bladed
aerofoil design, like the one wikipedia shows to give an example. To get around the self-start problem
the outer surfaces will have nicks cut out of them to allow some drag to start the thing.
     So, now the intro's out the way, I have a couple of questions for anyone that could advise me; 
- What kind of bearings should I use ( axle width maybe around 10mm+) for greatest ease of movement
and also how does a friction factor of a bearing translate into a coefficient that I can use when trying to
create an equation to determine the potential power output at different wind velocities?
- Second, should the wings have any sort of angle of attack relative to the wind (I have looked briefly
into self- regulating pitching mechanisms but again I am a little low on time)?
Thanks for any help in advance,
Dan

[electrondady1]

you haven't given a proposed swept area so its difficult to know what forces are involved
 a 10mm shaft would be better suited to a vertical  with a bearing at both the top and bottom

it could transfer a fair amount of torque but wont stand much bending moment.
and there will be a lot of side loading .
 if you go with no top pin you will need a much more substantial centre shaft.

[nemorocksharder]

Sorry, this is another thing I forgot to mention, I have been looking into equations for swept area, and while I have seen the common 'rotor height x chord length' used, I have also seen some more complicated versions so I haven't factored that in yet, I was going to get a big spreadsheet and just play with the numbers to see what would be ideal for the kind of turbine I wanted to build. Could you give me an equation for swept area or should I just use the aforementioned one?
cheers

[electrondady1]

well,
 the equation for swept area is about the only one i can give you

lxw=swept are

i sent you the link  to the wind gen forum, all the stuff you need is in there
keep your cards close to your vest
keep your hands in your pockets.

[electrondady1]

you could use the cord width x length to figure solidity against swept area.

[GoVertical]

Hi, consider that VAWT are slow. You need a PMA that can produce a charge current at a low RPM. Start charging a 50 RPM and than max out at 150 RPM. You may want to consider a Drag style and use a belt drive transmission.  Convert the torque to increase RPM and you would have a working project.

[XXLRay]

consider that VAWT are slow

This only applies to drag type turbines. The Darrieus (usually) is (or at least should be) a lift type turbine. It can (and should be designed to) have a tip speed ratio of five or more.

A 10mm shaft is still to thin in my opinion. Go for something of at least 18mm.

The trailing edge usually is turned about 5° to the center to create lift forces. You could even think about using a cambered profile.

Regarding the self starting problem you should rather think of using an uneven amount of blades e.g. three. My experience is that the darrieus starts quite well this way. You could also add little Savonius Rotors to improve self staring capabilities like here: http://de.wikipedia.org/wiki/Datei:Taiwan_2009_JinGuaShi_Historic_Gold_Mine_Combined_Darrieus_Savonius_Wind_Turbines_FRD_8638.jpg

As it is mounted on a boat all materials (also the bearing) should be salt water resistant.

[GoVertical]

Hi, lift, drag, hybrid  you should know the operational bandwidth of the PMA you going to use.  Rubber sealed bearings.  I hope to see some photos of the project. Best regards

[GoVertical]

http://www.windstuffnow.com/main/darrieus_type.htm

Hope this helps, enjoy the day.

[GoVertical]

http://www.thebackshed.com/windmill/photos2.asp

http://www.cyberiad.net/library/pdf/we1992_16_5.pdf

Hi, a few more links that may help. Maybe you can start a post in the diary section and keep us updated on your project.

[nemorocksharder]

OK so this is what I have gathered so far, and again I appreciate the advice as you all have been doing this a lot
longer than me;
- Shaft diam. should be atleast 18mm for the type of turbine I wish to build
- I should use 3 blades to increase the self- starting capability of the turbine
- There is a potential to implement a camber into the turbine (although Wiki mentions that this can lower the
stalling speed, however if the angle of attack isn't changing this might not be a problem?)
- Possibly augment the design to introduce a small savonius to help with self starting (although I would like as little
drag as possible)

A little more information; I am using a 24V DC, 6A motor as generator, it's rated output is 100W so with the help
of P=IV that makes it about 69.4% efficient. Also could someone define PMA please? Furthermore I am still
uncertain as to how the swept area is calculated; is it blade height x width (not thickness)? it's just quite hard to
visualize as with a HAWT it's just pi*r^2, but with a VAWT the wind interacts with a cylinder shape.
Although it is an engineering project you're supposed to get the materials yourself, and although I reckon I could
get the shaft and metal for most of the parts from the workshop, I am not sure how far I can push it so costy is
 a bit of an option (being a student). Lastly, I mentioned about the bearings having an impact on the efficiency-
I can't really find anything on the internet that describes a conversion method between relative friction and
power output so it would really have to be through experimental analysis of the workin turbine which is a while
away yet, so I might just have to leave that out of the calculations,
Thanks again,
Dan

p.s. I will start taking photos etc and putting them on a diary as soon as I start building it

[TomW]

PMA=Permanetnt Magnet Alternator.

[GoVertical]

Hi, Lowes and Tractor Supply Central (TSC) is a good place to purchase the hardware.
About the only item I was unable to find there is a hub assemble to attach the blade rotor to the main shaft.  Swept area may be ½ base time the height?  You may want to consider attaching the DC motor to the battery and use a hand crank and take some current measurements at different RPMs just to have a tactile sense of the forces required. Just a suggestion. I look forward to the photos enjoy the day.   

  Real important do not forget your diodes………..

[tanner0441]

Hi

You say you want to use a 24V motor as a generator, I have several 24V DC permanent magnet motors and the all run at around 5000 RPM. I assume you want to charge a 12 V battery which means your motor has to spin at over 2500 RPM.  If you only want to light a few LEDs to prove the principal then a stepper motor from an old printer would be easier.

Brian.

[itsandbits]

this is my own unit doing start stop tests.
http://www.youtube.com/watch?v=TQCTdWDVpUA
just an idea of what kind of power the right wing and configuration can give you.
Don't be afraid to just go with a lift wing. These give me 9n of start from stopped position. To get the rpm you need for that motor though, you do need to get the rpm up and in a past unit I used a 120v 2300 rpm motor salvaged from door operators that put out 12v at 90rpm which is easily attaineble with a lift vawt, this one does that in a 1mps wind.

[nemorocksharder]

My motor is rated at 2500 rpm at that voltage and current, so I'm hoping it will be OK,
'itsandbits', your turbine is scarily fast, what kind of aerofoil profile did you use as it's slightly hard to tell
from the video even if I pause it? Also I live in the UK so ordering things from the US is a bit of a pain,
cheers

[XXLRay]

Furthermore I am still
uncertain as to how the swept area is calculated; is it blade height x width (not thickness)? it's just quite hard to
visualize as with a HAWT it's just pi*r^2, but with a VAWT the wind interacts with a cylinder shape.

For a VAWT it is height times width of the turbine when you look at it from the wind direction. In your case it is blade height times rotor diameter if you are not heading towards an egg beater type.

[itsandbits]

My motor is rated at 2500 rpm at that voltage and current, so I'm hoping it will be OK,
'itsandbits', your turbine is scarily fast, what kind of aerofoil profile did you use as it's slightly hard to tell
from the video even if I pause it? Also I live in the UK so ordering things from the US is a bit of a pain,
cheers

Hi Nemo
the wing is my own developement starting with something that was a cross between this looks like it should fly well and I think it should start better. I actually started working on a drag /lift combo that looked similar to the lenz but with a kink. When I got on the internet I was accused of copying it so I dropped it and started working on a basterdized version of the original and it worked all right but then I found lift and saw the light. It's come a long ways and starts like crazy under load and has some decent top end too. Doesn't make a sound when it's running either which everyone likes. If you youtube Remkick you'll see some of my expiriments
Lloyd

[nemorocksharder]

Thanks, I had a look at your videos and they're pretty interesting,
I have been researching bearings all morning, and was thinking that they would need to support a thrust load through the bore of the bearing (i.e. the interior surface of of the bearing bore would have to support the turbine's weight) but have since realized that I could just embed a ball bearing in the end of the bottom of the turbine shaft that could sit in a smoothed area of the housing, in a small oil sump, and this could support the weight of the turbine. I am interested to know what are the best chord width to length ratios for a darrieus and how far the support bars should be positioned from the leading edge?
Sorry I am taking so long to post anything, I have quite a lot of other work on at the moment and it's difficult to get my ass into gear to start building,
thanks again,
Dan

[Bruce S]

Hi Nemo
the wing is my own development starting with something that was a cross between this looks like it should fly well and I think it should start better. I actually started working on a drag /lift combo that looked similar to the Lenz but with a kink. When I got on the internet I was accused of copying it so I dropped it and started working on a bastardized version of the original and it worked all right but then I found lift and saw the light. It's come a long ways and starts like crazy under load and has some decent top end too. Doesn't make a sound when it's running either which everyone likes. If you YouTube Remkick you'll see some of my experiments
Lloyd

Lloyd;
 I'm curious about the "accused of copying it" statement. Did someone here make this statement? OR internet nagging ?
ED is/was a long time poster here and has his own website. Only one place That I know of copied his design and sold it as theirs.
I don't see where you are trying to sell his design as your, but I may have missed it.
IF Ed asked you not to sell it as your design , that's one thing. IF some others did well might be a different story.
The #7 was very nice to watch speed up/slow down.
With it doing as well as it is doing, maybe the alternative designs are for the best 
Cheers, AND NICE work 
Bruce S
PS> NICE view in the background too!!