Home  |  Contents 

Windmills
  Forum Index : Windmills         Section
Subject Topic: My unorthodox Build Post ReplyPost New Topic
<< Prev Page of 13 Next >>
Author
Message << Prev Topic | Next Topic >>
BarkyJ
Senior Member
Senior Member


Joined: 26 April 2018
Location: New Zealand
Online Status: Offline
Posts: 113
Posted: 11 June 2018 at 10:09am | IP Logged Quote BarkyJ

Yep I have found a number of calculators, and all of them made very large root, like 400mm+, absolute monsters.
They were huge, I printed one out to scale and put it on the pipe, but it just seemed rediculous.


Back to Top View BarkyJ's Profile Search for other posts by BarkyJ
 
Warpspeed
Guru
Guru


Joined: 09 August 2007
Location: Australia
Online Status: Offline
Posts: 1946
Posted: 11 June 2018 at 10:39am | IP Logged Quote Warpspeed

Without ever trying one of those calculators myself, I can well believe that the mathematical extremes reached can be pretty radical when converted into actual hardware.

My gut feeling tells me there is not a lot to be gained right down near the hub anyway, there is just no leverage down there, so you could probably trim back the trailing edge a whole lot without losing very much.

As far as flow separation and turbulence go, its the angle of the leading edge that I believe is absolutely critical, and where you need to have the twist. If the flow is going to become unstuck and turbulent, you want that to occur as far back near the trailing edge as possible.

So I would try very hard to get the leading edge correct with some twist, and slim down the trailing edge if it gets really crazy huge down near the hub.

If you can make a long skinny oven out of some insulated airconditioning duct and a heat gun, or something along those lines, with extra heat and extra insulation, if you clamped your blades between two wooden masters and let it heat soak for a few hours that should work.

My own experience with PVC pressure pipe used in commercial swimming pool heating is that it starts to sag at about 80 Celsius. If due to some system control fault it ever gets that hot, the PVC deforms permanently. I have seen this sagging pipe effect both with solar and gas boiler heating, that went horribly wrong.



__________________
Cheers, Tony.
Back to Top View Warpspeed's Profile Search for other posts by Warpspeed
 
Boppa
Guru
Guru


Joined: 08 November 2016
Location: Australia
Online Status: Online
Posts: 560
Posted: 11 June 2018 at 10:46am | IP Logged Quote Boppa

I noticed that some of the big wind gennies use winglets at the tip of the blade, similar to what planes use on the ends of their wings, apparently it increases lift and reduces noise
Back to Top View Boppa's Profile Search for other posts by Boppa
 
Warpspeed
Guru
Guru


Joined: 09 August 2007
Location: Australia
Online Status: Offline
Posts: 1946
Posted: 11 June 2018 at 10:55am | IP Logged Quote Warpspeed

Yes vortex formation at the tip is a real noise maker.

The air flows around the outside edge from the high pressure side to the low pressure side which starts a vortex forming right at the tip.

Its why the tips of wings and propellers are usually rounded. Another solution is with a little fence along the tip of a square ended wing or blade. This was also the basis of Alan Bond's famous "winged keel" when he was Americas Cup yacht racing.

It cuts down drag and in the case of a wind turbine noise. Slim blades with a rounded tip also work well and look a lot neater, but if you are trying to get max efficiency with minimum length, a flat ended blade with a fence is the only real option.

__________________
Cheers, Tony.
Back to Top View Warpspeed's Profile Search for other posts by Warpspeed
 
BarkyJ
Senior Member
Senior Member


Joined: 26 April 2018
Location: New Zealand
Online Status: Offline
Posts: 113
Posted: 11 June 2018 at 11:00am | IP Logged Quote BarkyJ

Certainly is interesting stuff

What do you guys make of this one? Just the concept, more than the actual thing.

https://www.youtube.com/watch?v=4Pa3-pVYSLQ

He has it so the straight side is the leading edge, and the side with the fat heal is the trailing edge. Which is opposite to other pipe blade setups you typically see...
Back to Top View BarkyJ's Profile Search for other posts by BarkyJ
 
Madness
Guru
Guru
Avatar

Joined: 08 October 2011
Location: Australia
Online Status: Offline
Posts: 2307
Posted: 11 June 2018 at 11:03am | IP Logged Quote Madness

If you look at the little FPV racing Drones the props on them have the tip angled back at about 45 degrees to reduce noise and improve efficiency. They do massive RPMs, saw a little one yesterday with 3" props and the thing can do in excess of 160KMH.

__________________
Staying in my backshed where it is more peaceful!
Back to Top View Madness's Profile Search for other posts by Madness
 
BarkyJ
Senior Member
Senior Member


Joined: 26 April 2018
Location: New Zealand
Online Status: Offline
Posts: 113
Posted: 11 June 2018 at 11:25am | IP Logged Quote BarkyJ

Check these Winglets out

https://www.youtube.com/watch?v=HP3aAa_w2S4
Back to Top View BarkyJ's Profile Search for other posts by BarkyJ
 
Madness
Guru
Guru
Avatar

Joined: 08 October 2011
Location: Australia
Online Status: Offline
Posts: 2307
Posted: 11 June 2018 at 11:40am | IP Logged Quote Madness

That is very similar to the little drone props.

__________________
Staying in my backshed where it is more peaceful!
Back to Top View Madness's Profile Search for other posts by Madness
 
Bryan1
Guru
Guru
Avatar

Joined: 22 February 2006
Location: Australia
Online Status: Offline
Posts: 871
Posted: 11 June 2018 at 9:48pm | IP Logged Quote Bryan1

http://www.alton-moore.net/wind_calculations.html

Been using this wind blade calculator for years and it is pretty accurate
Back to Top View Bryan1's Profile Search for other posts by Bryan1
 
BarkyJ
Senior Member
Senior Member


Joined: 26 April 2018
Location: New Zealand
Online Status: Offline
Posts: 113
Posted: 12 June 2018 at 7:12am | IP Logged Quote BarkyJ

Hi Bryan1,

This was one of the first ones I had seen actually, but it says the same sort of thing. At the root, its like 400mm wide. That is massive.



Just doesn't make a lot of sense to me right now...
Back to Top View BarkyJ's Profile Search for other posts by BarkyJ
 
Madness
Guru
Guru
Avatar

Joined: 08 October 2011
Location: Australia
Online Status: Offline
Posts: 2307
Posted: 12 June 2018 at 7:29am | IP Logged Quote Madness

You might have missed this part.

Please note that near the hub you will usually be limited as to the blade's angle/slope, chord, and thickness by the size of the material. Usually it will suffice to use the largest result which fits in the material you are working with, or just carve the flat side of the prop from one corner to the other of the (rectangular) material. The outer part of the prop is the most important anyway.

__________________
Staying in my backshed where it is more peaceful!
Back to Top View Madness's Profile Search for other posts by Madness
 
BarkyJ
Senior Member
Senior Member


Joined: 26 April 2018
Location: New Zealand
Online Status: Offline
Posts: 113
Posted: 12 June 2018 at 7:37am | IP Logged Quote BarkyJ

I did miss that, thanks.

So is that saying, if the above table doesn't fit the material, then just wing it, and make it as big as you can at the root, and 'she'll be right'... ?
Then its basically a taper from the root to the tip.

Problem with the pipe is all the slops and stuff are not exactly easy, or possible to replicate.

I think ill just keep going with my hack job I am doing now, and see how they perform.

Back to Top View BarkyJ's Profile Search for other posts by BarkyJ
 


<< Prev Page of 13 Next >>
In the news...
 
Post ReplyPost New Topic
Printable version Printable version
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot delete your posts in this forum
You cannot edit your posts in this forum
You cannot create polls in this forum
You can vote in polls in this forum

Powered by Web Wiz Forums version 7.8
Copyright ©2001-2004 Web Wiz Guide

This page was generated in 0.1250 seconds.
Privacy Policy     Process times : 0, 0.02, 0, 0.11