Optimizing Efficiency: Wind Turbine Blade and Hub Design Tips?

[Avvai Chandrasekaran]

I'm building a model wind turbine. I'm using thttps://www.vernier.com/products/kidwind/wind-energy/kw-wth3/ as the hub/the base. That's the only kit I'm allowed to use.
I'm supposed to decide on the blade size, etc.

THE RULES:
. Students will will sign up for a time slot and test their own devices in front of the judges. Students will have 30 seconds to set up prior to testing.
3. The device must pass a GO-NO-GO inspection including a safety inspection to insure no harm or damage will occur. Any unsafe devices WILL NOT BE TESTED and be counted as a disqualification.
4. The device must meet the following specs:
• Stand Height: 24 in (must use stand with gear box system provided by GATSA)
• Maximum blade diameter: 36 in
• Maximum number of blades: 12
• 4 Box fans will be used to create a wind tunnel (2 fans on bottom with 2 fans on top). Wind tunnel will be 48inx48inx48in cube open on the back
• Voltage will be measured using a multimeter attached to the generator leads
• Student will have three opportunities and the three voltages will be averaged.
• Award places determined by voltage ranking
• Ties will be broken by testing efficiency of the wind turbine

What I need is not a step-by-step of how to build one. I'd appreciate tips and basic principles.
Thank you for reading.

 

[berkeman]

I'm building a model wind turbine. I'm using thttps://www.vernier.com/products/kidwind/wind-energy/kw-wth3/ as the hub/the base. That's the only kit I'm allowed to use.
I'm supposed to decide on the blade size, etc.

THE RULES:
. Students will will sign up for a time slot and test their own devices in front of the judges. Students will have 30 seconds to set up prior to testing.
3. The device must pass a GO-NO-GO inspection including a safety inspection to insure no harm or damage will occur. Any unsafe devices WILL NOT BE TESTED and be counted as a disqualification.
4. The device must meet the following specs:
• Stand Height: 24 in (must use stand with gear box system provided by GATSA)
• Maximum blade diameter: 36 in
• Maximum number of blades: 12
• 4 Box fans will be used to create a wind tunnel (2 fans on bottom with 2 fans on top). Wind tunnel will be 48inx48inx48in cube open on the back
• Voltage will be measured using a multimeter attached to the generator leads
• Student will have three opportunities and the three voltages will be averaged.
• Award places determined by voltage ranking
• Ties will be broken by testing efficiency of the wind turbine

What I need is not a step-by-step of how to build one. I'd appreciate tips and basic principles.
Thank you for reading.

Welcome to the PF.

If they are truly just measuring the open circuit voltage output of the generator circuit, there's an easy way to win! But they must be planning on using some sort of load for the generator output, no? What else are you given about the load? It's important to know that. (Quiz Question -- Why?)

What reading have you been doing about the efficiency of various windmill blade designs? Have they given you any idea of the wind velocity that will be generated in the "wind tunnel" during testing?

What other rules are there? Are you allowed to build your own "Maximum Power Point" converter circuit for the output of the generator? Do you know what that is?

 

[Tracey3]

I have done something similar in the past, however I am not aware of your current level of understanding of aerodynamics etc. So I will give you this PDF:
https://www.google.co.uk/url?sa=t&rct=j&q=&esrc=s&source=web&cd=11&ved=0ahUKEwi0_-CLqITWAhUGY1AKHc3uDYAQFghqMAo&url=http://www.mdpi.com/1996-1073/5/9/3425/pdf&usg=AFQjCNEznBNRj-fWG5MwcGV6lJqiisilNQ

It throws a fair bit of concepts and words at you but I found it to be a good jump off platform for blade design. In the competition that I did you only had to design the blades and they also awarded points for ingenuity. A lot of people fell behind because there surfaces weren't smooth. So I recommend you hot wire it out of foam and use clear duct tape then you could reinforce it with carbon fibre or wood depending on the diameter. Then again as @berkeman said, 4 box fans doesn't tell us much about the wind speed. Because foam will work fine for 4 on the Beaufort scale but let's say its 10 and we have a problem

 

[Avvai Chandrasekaran]

I have done something similar in the past, however I am not aware of your current level of understanding of aerodynamics etc. So I will give you this PDF:
https://www.google.co.uk/url?sa=t&rct=j&q=&esrc=s&source=web&cd=11&ved=0ahUKEwi0_-CLqITWAhUGY1AKHc3uDYAQFghqMAo&url=http://www.mdpi.com/1996-1073/5/9/3425/pdf&usg=AFQjCNEznBNRj-fWG5MwcGV6lJqiisilNQ

It throws a fair bit of concepts and words at you but I found it to be a good jump off platform for blade design. In the competition that I did you only had to design the blades and they also awarded points for ingenuity. A lot of people fell behind because there surfaces weren't smooth. So I recommend you hot wire it out of foam and use clear duct tape then you could reinforce it with carbon fibre or wood depending on the diameter. Then again as @berkeman said, 4 box fans doesn't tell us much about the wind speed. Because foam will work fine for 4 on the Beaufort scale but let's say its 10 and we have a problem

The rules didn't say anything else about the wind speed. They just said 4 box fans. :/

(Also, please check my reply to @berkeman. It has more information.)

 

[Avvai Chandrasekaran]

Welcome to the PF.

If they are truly just measuring the open circuit voltage output of the generator circuit, there's an easy way to win! But they must be planning on using some sort of load for the generator output, no? What else are you given about the load? It's important to know that. (Quiz Question -- Why?)

What reading have you been doing about the efficiency of various windmill blade designs? Have they given you any idea of the wind velocity that will be generated in the "wind tunnel" during testing?

What other rules are there? Are you allowed to build your own "Maximum Power Point" converter circuit for the output of the generator? Do you know what that is?

Like I mentioned before, I'm very new to all of this. I joined on a whim, just to see what I could do. So forgive me for not understanding most of the lingo and jargon that's common in engineering fields.

So, my first questions would be: what do you mean by 'load'? Like measurement of energy?

I've being looking around, but most of the material seems to be hard to digest. I'll definitely be looking for more reading material-- I've got a fair bit of reading to do.

As far as I know, these are all the rules. And I don't know what a Maximum Power Point converter circuit is... I'm sorry, haha.

I'm sorry for not replying earlier, and I'm even more sorry for not being able to understand a lot of what you're saying. Thank you for all your help!

 

[berkeman]

I'm even more sorry for not being able to understand a lot of what you're saying.

No need to be sorry at all. You are doing good things to learn more!

So, my first questions would be: what do you mean by 'load'? Like measurement of energy?

Well, if there is no output load (like a light bulb or something), then the output voltage can be arbitrarily high and not get loaded down. It takes very little energy to power a circuit that boosts the output voltage to very high values. If there is an output load like a light bulb or a resistor, then you are limited in how high the output voltage can go. If you have an output load of Power=1.2W, then your output voltage and current could be V=12V at I=0.1Amp (P=V*I). If they connect a lower resistance load, that will pull down the output voltage.

I'll definitely be looking for more reading material-- I've got a fair bit of reading to do.

Yeah, just look for some basic introductory electronics tutorials for now. That should give you a better background for the basic electrical stuff you will be working with in this project. Here is a link to some basic electronics concepts at Hyperphysics, for example:

http://hyperphysics.phy-astr.gsu.edu/hbase/electric/ecircon.html

 

[JBA]

Just as an exercise, I figure that 4 box fans set in a 4 ft sq box end would have a maximum fan size of 12" or less and for one typical industrial 12" box fan the delivery rate is 1360 cfm; which, for 4 fans in a 4 ft sq duct, as specified, results in a wind speed of just under 4 mph.

I have no background to judge how this relates to the blade or unit design; but, maybe it would mean more to one of the other members of the forum with more experience in this area; but, to me it would tend to indicate that a broad blade design tending toward a standard house fan blade would be more appropriate than a more standard wind turbine blade design. At the same time this would seem to be a "power" vs "speed" issue as well.

Any thoughts or comments, anyone?

 

[JBA]

This might give a clue on a new blade shape to investigate

http://www.aliexpress.com/item-img/...ding-Kids-Party-Prom-Supplies/2023562772.html

 

[berkeman]

This might give a clue on a new blade shape to investigate

http://www.aliexpress.com/item-img/...ding-Kids-Party-Prom-Supplies/2023562772.html

 

[scott mcfee]

I want to know what NASA has been doing with blade design. Maybe some of that can be used here?

 

[berkeman]

I want to know what NASA has been doing with blade design. Maybe some of that can be used here?

Sounds like a plan. Links?

And Quiz Question -- what would be different between the NASA designs and the design that will fit the OP's project the best?

 

[JBA]

In doing a bit of searching on blade designs I came across the below discussion on ceiling fan design by Moore fans; and, at one point (on pg 6) where it proposes that for low speeds a large center hub (i.e. possibly a cone shaped hub) that directs air flow outward the surrounding blades and increases the air velocity at the blades is effective in improving fan efficiency.

http://www.moorefans.com/pdfs/TMC_661P_.PDF

While not relevant to the NASA issue, it does raise a design concept I had not seen addressed in any of my prior searches on blade or propeller designs.

 

[dmac257]

you need to know a lot about the environment you are going to be tested on .. blade design for 4mph wind would be different that for 40mph. I re-read your OP and it sounds like you are only designing the blades that must be attached to the stock hub and you are not changing the actual generator itself?? 30 seconds to set it up, but is each of the three tests TIMED or does it end when you get fully up to speed and get a steady voltage?

dmac257

 

[scott mcfee]

I agree with your comment on blade and hub design. There is likely a separate subject on wind turbine blade design.I am guessing you would have to build a "wind tunnel" to test propeller design. If you have a 36 inch prop., how big would you want to make the wind tunnel? 48 inch? I wonder if the best way to test a propeller design is to blow a certain cfm (mph wind) of air at the propeller and see how much electricity is generated? I am not sure what power supply(briggs and stratton?) or blower you would use to make the "wind"
I think you would have to have a stable air supply.(wind) An accurate wind meter. An accurate amp meter. You could see how much power is made at 2mph wind- 3 etc.

 

[CWatters]

One of the variables is blade pitch. I suggest you make it adjustable so you can optimise it on the day.

 

[anorlunda]

The OP did not resolve @berkeman's question about the load. That is an all important question.

Wind turbines are interesting because they make power. Better blade design makes more power. But electric power output is a product of voltage V and current I. P=V*I. So if there is no load (a load is something that consumes power), I=0 and P=0, V can be anything. Therefore it makes no engineering sense to judge the contest based on V without saying something about the load. Supplying a load is normally the only purpose of building a wind turbine.

But it is also possible that the contest rules are faulty and did not consider load. In that case there are winning strategies that have nothing to do with good blade design (as @berkeman hinted at)

It is essential to find out the answer to the load question.

 

[CWatters]

+1 on the load issue, although we shouldn't forget that the generator/gearbox might have quite a bit of friction, especially if it's a step up gearbox.

 

[scott mcfee]

hmm. I think dmac257's comment is most correct/interesting. I think he is correct about the difference in blade/ hub design at low wind versus high wind.While a variable blade is good- it does not address what blade/ hub design combo is best.Who has any idea about how efficient blade design is at 2 mph wind or 40 mph wind? To me the most efficient blade/ hub design will produce the most electricity.Is that not what it is about? What is the theoretical best efficiency for a wind turbine at 2 mph? at 40 mph? What is the current (no pun intended) average efficiency of a wind turbine at 2 mph? at 40 mph? If I am building a wind turbine- I want to know where I am now, aka what is industry average efficiency. I then want to know what is the best it can be. That info enables me to acquire the target. I think the cost to R&D blade/ hub design is astronomical.Is NASA the leader in propeller blade design? Will they release all their info?