Helical ducted fan? Has anyone seen this before? 3

[Anata]

I am a total newbie when it comes to aerodynamics but I was trying to do some research on ducted fans and propeller types that being used or in the experimental stage. I have this concept for a type of ducted fan; I guess you would call it that, but I am not sure how efficient this would be or if it has been tested before. I know almost nothing about the history of aerodynamics so if this is old news please let me know. I have two rough models of my idea here:

http://www.digitalife.org/side.jpg

http://www.digitalife.org/side2.jpg

It's basically a screw-type system that I know is used in other industries to convey small objects or liquids. I know that there are air compressor systems that use a similar method for constant flowing air but I don't know how efficient it would be for propulsion.

I would really appreciate any help with where to research this or if it's old news or if it already has a name. Anything would be helpful.

Thanks,

John

 

[MikeHalloran]

Screw compressors with similar rotors also have complementary intermeshing rotors. The paired rotors trap pockets of fluid and physically move them from one end of the device to the other.

The mechanism you have drawn is called an Archimedes screw conveyor. If you tilt it at 45 degrees or so, and reduce the tip clearance, it will lift water from one canal to another when the shaft is rotated. It is also used for lifting grain and such; you could probably find one on most any farm.

Submerged in water with the axis horizontal, you could use it as a thruster on a boat. In fact, very short versions are built into crosswise tubes in the hull of yachts for steering at low speeds. Search on 'bow thruster'.

Contrast it with the fan on an airliner's turbofan engine, which is better adapted for use with a compressible fluid.




Mike Halloran
Pembroke Pines, FL, USA

 

[Anata]

Thanks for the information Mike. I will look into those things. If I understand correctly, this type of device is better suited for liquids and not air. This would not work well as a propeller for an aircraft, correct?

Thanks again,

John

 

[pennpoint]

MikeHalloran
Right on fine post! For sure.
A star, again!

pennpoint

 

[AeroAd]

As MikeHalloran said, you're better with a conventionnal propeller or a turbofan (if you want hight performance). Keep in mind that the Archimedes screw conveyor moves matter, wich principle is not effective for compressible fluids. A propeller create a pressure difference like the wings of an airplane (low pressure forward) that 'pull the airplane'. You will not be able to create a good pressure difference with an Archimedes screw conveyor.

Adam
Québec, Canada

 

[Anata]

Adam,

I see. That makes sense. Thank you as well for the explaination.

John

 

[pyro]

Another effect would be a significant radial component of the exiting velocity and a relatively small axial component, making it an inefficient propulsor.