Designing/Purchasing Hydro Turbine Blades

[HydroGuy]

I work at a small company and we're currently developing a hydrokinetic turbine device that will operate in fast flowing rivers to generate electricity. Eventually, we are going to design our own custom turbine blades, but for initial testing purposes we are simply trying to find something that will do the job.

For our testing, let's assume 1/4 scale or smaller, testing in a controlled environment. It will initially be a very primitive setup. I'm talking a small Ametek DC motor/generator hooked up to the turbine blades and doing some extensive initial work just to get a foundation. I can easily find generators, but finding turbine blades is proving to be tough work.

I'm an intern and this is my first OTJ engineering experience, so I'm not very efficient in finding what I want. I have contacted a few marine suppliers and have found some larger boat propellers that MAY work, but would be far from ideal...

Here are the boat props I'm looking into: http://boatpropellers.iboats.com/Vo...andard&session_id=315413786&cart_id=710966203

Our testing will be in water speeds between 2 and 6 m/s, and I have my doubts that this propeller will provide the power in these conditions to turn any generator effectively.

Meanwhile, seeing as how this product is similar to a wind generator (except underwater) I've been looking into wind turbine blades as well for the initial testing, such as these...

http://www.windynation.com/shop/index.php?act=viewCat&catId=2

These would probably work better than the boat prop at turning the generator, but I'm afraid they would probably break or warp easily, and I'm not sure how much RPM they will generate.

Side note: Does anyone have any formulas for relating turbine blade diameter, pitch, efficiency, and power?

I'm continuing to search for turbine blades that would work well in water... any ideas or options on what to do, who to contact, etc would be GREATLY appreciated.

Thanks for any help in advance...

 

[Topher925]

Chances are your going to have to make your own. A boat propeller is designed to be a propeller, not a turbine. A wind turbine is designed to work in wind, not fast moving water current. Wind turbine blades have enough trouble with aeroelasticity in air alone and would most definitely fail in water. So in short, no, neither will work well if at all for your application.

Go to google and check out some of the designs for underwater turbines. You will see that they all have very specific common design traits. I think your best bet at finding a working turbine is to use a modified aircraft propeller. (think ultralight)

http://apolloalliance.org/digest/wp-content/uploads/2008/08/tidalpower.jpg

Side note: Does anyone have any formulas for relating turbine blade diameter, pitch, efficiency, and power?

For power with respect to diameter and velocity, yes. Newtons second law and Betz's law. For pitch and efficiency, no that is a lot more complex then just using some simple formulas. You can ballpark a solution to maybe 50% error using conservation of momentum and blade element theory.

Newtons Law: F = ma

Power = 0.125 x p x pi x d² x V³ x 0.59

Where d is the diameter of the turbine, and V is the velocity of the water, and p is the density of the water.

The 0.59 is because of Betz's law which states the most power an open turbine can convert from fluid flow is 59% of the kinetic energy in that fluid flow.

I highly suggest you pick up a good fluid mechanics text and read up on turbo machinery. I recommend "Fluid Mechanics" by Frank White.

 

[apc3161]

The first thing I would do is find a good graph of the efficiency of a turbine versus its specific speed. There is a good example is many turbomachinery books. I have "Principles of Turbomachinery " by Shepherd that has a good example on page 39. This will let you know whether you should probably go with a Pelton wheel, Francis turbine, axial turbine (propellor), etc.

My guess is that at your speeds you will probably go with a pelton wheel or a Francis turbine to get maximum efficiency. I doubt an axial flow propellor will bring you good efficiencies at that speed. Good luck.

 

[vkm]

Betz law is applicable to wind turbine and not for hydro,is it?