very low head turbine

[acme12]

Hi, I have few questions for very low head (0.7 m) propeller turbines.

My friend has a software PropCad that could generate ducted boat propellers. Should hydro propeller be made with characteristics for boat propellers by use the mirror hydro foils?

What characteristics  should be used for low head propeller, blade number, hub diameter (%/D), expanded BAR, blade thickness distribution, nominal pitch or TSR...?

Available flow is more then 200 l/s. Used flow will be lower, reduced by PVC penstock and runner both in diameter 300 mm.

Thanks for answers.

Marko

[tanner0441]

Hi

Boat propellers are designed to put power into the water not extract it, if you are talking about the type of ducted propellers as used in jet skis they are a positive displacement pump.  ie.  The blades overlap each other to prevent bipassing of the water, add to this the clearance between the blade edges and the duct is around 10 thou. you would need very clean water going into it.

The ordinary Mercury type of boat propeller will turn when being towed if the gears are in neutral but slowly and with very little torque.

Brian.

[scottsAI]

acme12,

Look into Banki turbine.

Turbine of choice for low head and something DIY can build.

Have fun,

Scott.

[spinningmagnets]

I "think" the propellor style of hydro impellor is called a "Kaplan", looks similar to boat propellor from a distance, up close many differences, and the higher the head the better. I have read about a Kaplan being used with a 7-foot head:

http://www.fieldlines.com/story/2008/6/22/191210/965

[Flux]

The Kaplan is the one to go for for low head. It is similar to a boat propeller but with the aerofoil reversed and the blade angle can be changed to suit the flow. It is used with a vortex chamber and effectively works in the throat of a venturi. Most likely it will have 4 blades. Your flow is reasonable but the head very low even for a Kaplan. Monster tidal ones may work down to this head with good efficiency.

Flux

[acme12]

Hi all

Flux,

I was thinking to use reversed aerofoil too. Does the pitch (blade angle)must be changed.

Is there realy need to have wider penstock then runner, to have ventury. I intended to use only draft tube behind runner. Something like this.

http://www.mackellars.co.uk/promosite/hydroturbines.html

What are you haveing in mind with "Monster tidal"

Thanks

[Flux]

I think you can probably get away without a volute chamber as long as you use guide vanes ahead of the runner.

What you can get away with with micro hydro may be a bit different form a 10Mw hydro set up where you are aiming for efficiencies up towards 90%.

There is still some logic in reducing the diameter at the runner to give a small venturi effect as it keeps the water velocity high and increases the pressure at the runner and avoids cavitation. The outlet ideally needs to expand towards the discharge point and that must be submerged.

I was thinking of the large tidal installations where the head is only a foot or so at the change of tide.

Propeller turbines work in the flow of streams so if you have enough water then the lack of head will not stop it working but things may become more critical.

Flux

[Gog]

Hi Acme

I think a 4ft diameter by 3ft wide breastshot water wheel may be a better option

Get your feet wet and have fun

Keith