Shape of an air driven turbine

[zydubion]

What is the most efficient shape of an air driven turbine?

I want to achieve the greatest possible torque with the lowest volume of air.

I hope I am posting this in the correct place. If not, any
links would be helpful. Thank you very much.

 

[russ_watters]

It depends entirely on the characteristics of the air you are sending through it. Essentially a turbine blade is a wing - and the best shape of a wing depends on the intended flight envelope. So what exactly are you trying to do?

High torque would probably mean getting the most from the air volume you can at low speed. So something the shape of a fan might be best. But that will also mean relativly low power output.

 

[enigma]

That is a very broad question.

You'll need to list a few more specifics.

Size/weight restrictions?
Cost constraints?
What type of project is it being used for?
etc.

 

[zydubion]

The application is for a small shop tool. The diameter of the turbine would be approximately 1.5 inches, while thickness should be less than 1/4 inch. Compressed air will enter the outer edge of the turbine via a nozzle. The output of the turbine will be interconnected to a substantial gear reduction and finallly to the work.

 

[Tyger]

Look at it logically.

For maximum torque you want the blade to turn as slowly as possible, because of the torque/speed tradeoff, so you want a turbine with the maximum diameter. A propeller type blade is designed to turn fast, so that isn't what you're looking for. You basically need a cenrifugal fan, but operating as a turbine. You can arrange to discharge the air through only part of the perimeter of the turbine to match the load characteristics.

 

[russ_watters]

Originally posted by Tyger
Look at it logically.

For maximum torque you want the blade to turn as slowly as possible, because of the torque/speed tradeoff, so you want a turbine with the maximum diameter. A propeller type blade is designed to turn fast, so that isn't what you're looking for. You basically need a cenrifugal fan, but operating as a turbine. You can arrange to discharge the air through only part of the perimeter of the turbine to match the load characteristics.

You're right, except that while he THINKS he needs high torque, what he really needs is high rpm and power output. The reduction gear takes care of the torque. But in any case, I'm not sure a pneumatic tool is something that can really be made at home.

 

[Ivan Seeking]

Originally posted by zydubion
The application is for a small shop tool. The diameter of the turbine would be approximately 1.5 inches, while thickness should be less than 1/4 inch. Compressed air will enter the outer edge of the turbine via a nozzle. The output of the turbine will be interconnected to a substantial gear reduction and finallly to the work.

from Russ
But in any case, I'm not sure a pneumatic tool is something that can really be made at home.

I agree. I would try to modify an existing device before re-inventing the wheel. There are plenty of pneumatic tools available for consideration. I would bet that one of them already fits the design criteria; ie. pressure, flow, [the total work required], in addition to considerations like the maximum duty cycle; and some other factors like maximum momentary toque and impulse, speed, etc.

 

[Tyger]

From his further description it sounds like he needs a compressed air motor, such as used in a garage, which is a vane type motor, and not a turbine at all.

 

[zydubion]

Perhaps I posted my original question incorectly. Sorry. What I should have said was that I am looking for a blade design that provides the greatest efficiency within the air motor or turbine itself. I want high torque at the air motor output and will of course increase that torque signigicantly via the gear reduction. I am looking for the most efficient use of the input air via a proven blade design. Your reply posts are appreciated.