Does an impeller need a driveshaft?

[theycallmevirgo]

TL;DR Summary

Is there any reason for an impeller driveshaft other than stability?

I have good basic FEA books, but all the stuff online is focused on chemical mixing.

Thanks so much

Joe

 

[berkeman]

Do the current offerings for watercraft impellers not meet the design goals for a design you are working on? What other factors do you want to improve upon? What are your design constraints?

https://www.google.com/search?client=firefox-b-1-d&q=watercraft+impeller+design

 

[theycallmevirgo]

Well, I just wanted to get a basic idea of what's going on. At this point I can't even select from available options on the market, and I strongly suspect that my application is going to be 50% the size of anything I can buy.

ETA: but I found a book already. I'll be posting another question shortly.

 

[berkeman]

I'll move your thread to the ME forum for better replies. Did you look through the hits in my link?

Also, please post your design constraints. We won't be able to help you unless you post your target dimensions, power transfer, water speed range, duct characteristics, etc. Thanks.

 

[theycallmevirgo]

Here's a picture of an impeller from J S Carlton (Marine Propellers and Propulsion 2nd edition 2007)

If I understand correctly, the driveshaft is there for the gas motor. If I had an electric motor, could I just use coils around the impeller? Or, alternately, can I drive an electric with gas?

Thanks

Joe

 

[berkeman]

I'll be posting another question shortly.

Multiple threads merged...

 

[theycallmevirgo]

Multiple threads merged...

Thanks for the help. I don't know half the terms you're listing as design constraints, which is why I need to do some reading. All I know for now is that I strongly suspect overall diameter is going to be 50% of anything on the market right now.

 

[berkeman]

If I had an electric motor, could I just use coils around the impeller?

Do you mean if you had permanent magnets on the impeller assembly, could you drive the impeller with coils on your stator? Yes, it's an active area of research and production...

http://www.change-climate.com/Trans...usters_Jet_Drives_Efficiencies_Technology.htm

Also paging @anorlunda

 

[theycallmevirgo]

OK, very cool. This is now a project worth pursuing.

 

[anorlunda]

If I had an electric motor, could I just use coils around the impeller?

Yes, there are several marine propulsion designs that do basically that. You may need a much bigger diameter of that duct. Here's one that uses permanent magnets. I'm not sure what their top RPM is. I just searched "marine magnetic propulsion".

 

[theycallmevirgo]

Yeah I looked at the first link, if their efficiency is as they claim it is very promising. Thanks for the help folks!

 

[theycallmevirgo]

Am I missing something, btw, wrt turbines? If they can be used for hydroelectric generation why not propulsion?

 

[anorlunda]

Am I missing something, btw, wrt turbines? If they can be used for hydroelectric generation why not propulsion?

Sure, marine turbines have been used for 100 years. But recently, diesel-electric has the competitive advantage.Also see this thread:
https://www.physicsforums.com/threads/remarkable-new-marine-propulsion-systems.972646/

 

[russ_watters]

Am I missing something, btw, wrt turbines? If they can be used for hydroelectric generation why not propulsion?

Turbines being spun by what? Your example of hydroelectric implies you think a water turbine could work here...

 

[theycallmevirgo]

Turbines being spun by what? Your example of hydroelectric implies you think a water turbine could work here...

Yes, that's correct, driven by emagnets.

 

[theycallmevirgo]

recently, diesel-electric has the competitive advantage.

Why do you think that is?

Also, just to make clear, I meant specifically turbine driven by em forces pushing water, not gas turbines pushing a prop (which I've seen numerous examples of).

 

[russ_watters]

Yes, that's correct, driven by emagnets.

"Driven" by magnets? Hang on, just to make sure we have our definitions right:

Impeller: spins and pushes water.
Turbine: is spun by water.

Turbines do not get driven by magnets.

 

[theycallmevirgo]

"Driven" by magnets? Hang on, just to make sure we have our definitions right:

Impeller: spins and pushes water.
Turbine: is spun by water.

Turbines do not get driven by magnets.

OK, let me rephrase, because I'm guessing I'm using the wrong terms. You have a hydro power turbine, which is rotated by water to make electric power. Why can't a (nearly) identical system use electrical power to move water for propulsion?

 

[russ_watters]

OK, let me rephrase, because I'm guessing I'm using the wrong terms. You have a hydro power turbine, which is rotated by water to make electric power. Why can't a (nearly) identical system use electrical power to move water for propulsion?

You can - the other guys have given several examples. I guess I'm not seeing what is unsatisfactory in what you've been given.

 

[theycallmevirgo]

You can - the other guys have given several examples. I guess I'm not seeing what is unsatisfactory in what you've been given.

Well, from my (super-cursory) overview the mechanisms used for generation are much more involved (and much closer to air propulsion turbines) than what was shown. But it's entirely possible I'm mistaken.

 

[Tom.G]

OK, let me rephrase, because I'm guessing I'm using the wrong terms. You have a hydro power turbine, which is rotated by water to make electric power. Why can't a (nearly) identical system use electrical power to move water for propulsion?

Turbines are internally much like a waterwheel, whereas an impeller generally resembles a fan.

By stretching definitions just a little bit, sidewheel and sternwheel boats could be called sideturbine and sternturbine driven. (Sidewheel aka paddlewheel)

Cheers,
Tom

 

[anorlunda]

OK, let me rephrase, because I'm guessing I'm using the wrong terms. You have a hydro power turbine, which is rotated by water to make electric power. Why can't a (nearly) identical system use electrical power to move water for propulsion?

That's what your impeller is. An electric motor turns the shaft and the impeller is a water turbine. That's where you started in this thread.

EM fields directly moving water is called magnetohydrodynamics. It has been researched for decades, but few applications exist. It was even the theme of a Hollywood movie named "Hunt for Red October"

https://en.wikipedia.org/wiki/Magnetohydrodynamics