Gas (Tesla) Turbine started

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Nick
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Gas (Tesla) Turbine started

Post by Nick » Tue Jul 04, 2006 7:23 pm

Hi All after many years of building pulsejets and admiring Gas Turbines an whilst waiting for materials for the phoenix project to arrive, ive started my first home built Gas turbine project.
Ive gone for a Tesla Turbine for two reasons

1. Its unusual, but ive built sucessfull air powered Tesla's before.
2. I can build pretty much all of it on my CNC mill and the rest i can do on my lathe.

Im building a prototype in acrylic first to run up the Tesla compressor to near operating speeds so i can get some figures about how much air and at what pressures it can produce.
To do this i am going to place the Turbine and compressor on a common shaft as in real GT practice but with no combustion chamber, I'll run the turbine up in compressed air and then measure the compressor output. This stage is crucial to the project as i have no figures at all to go by for the size that is within the operating envelope of my cnc mill.
Anyway pics attached of the test spindle machined up, ive spun it up on air and cant detect any vibrations or inbalances but im not that surprised as the blades are uniform thickness discs so the propensity for uneveness is less than that of a conventional centrifugal compressor.
Cheers

Nick
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spindle.jpg
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Dave_G
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re: Gas (Tesla) Turbine started

Post by Dave_G » Tue Jul 04, 2006 7:53 pm

Nick,

Before you go too far, you might want to do a bit of literature search on the internet first. There was a guy who, a few years back (I don't remember his name or the reference, or I'd give it to you) did exactly what you're trying to do. It didn't work because the efficiency of a 'Tesla Turbine' operating as a compressor is too low to sustain operation. I believe a gas turbine compressor needs to have about 65% efficiency minimum (when used with a fairly efficient turbine -- ~90%) in order to make a just self-sustaining engine. This leaves zero power for useful thrust. I don't recall the exact figures, but I think the Tesla compressor was somewhere around 45-55% efficient.
I could be wrong, but this is my recollection. You might want to check it out; might save you some trouble.
Again, if I recall correctly, the issue wasn't the turbine eficiency, it was the 'Tesla Turbine'-style compressor efficiency that was too low. Maybe you could use an automotive turbocharger rotor for your compressor, and a Tesla Turbine for your turbine?
Just a thought.
Dave

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re: Gas (Tesla) Turbine started

Post by Johansson » Tue Jul 04, 2006 7:57 pm

Hi Nick!

A very interesting project indeed, I have read about Tesla turbines and allways wondered if they could work in a gas turbine. The main difference as I remember it is that the turbine inlet nozzle design is extremely important, can a Tesla turbine work efficiently with the low combustor pressures inside a gas turbine?

Keep us updated!!!

//Anders

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re: Gas (Tesla) Turbine started

Post by Fricke » Tue Jul 04, 2006 8:02 pm

Very interesting topic!

Keep the posts and build pictures comming!

Tesla turbines are soo cool... =)

There was a guy in NZ that did build a tessa turbine many years ago... But the site is gone... and he didn´t finish the project..

//Fredrik

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Re: re: Gas (Tesla) Turbine started

Post by Nick » Tue Jul 04, 2006 8:22 pm

Dave_G wrote:Nick,

Before you go too far, you might want to do a bit of literature search on the internet first. There was a guy who, a few years back (I don't remember his name or the reference, or I'd give it to you) did exactly what you're trying to do. It didn't work because the efficiency of a 'Tesla Turbine' operating as a compressor is too low to sustain operation. I believe a gas turbine compressor needs to have about 65% efficiency minimum (when used with a fairly efficient turbine -- ~90%) in order to make a just self-sustaining engine. This leaves zero power for useful thrust. I don't recall the exact figures, but I think the Tesla compressor was somewhere around 45-55% efficient.
I could be wrong, but this is my recollection. You might want to check it out; might save you some trouble.
Again, if I recall correctly, the issue wasn't the turbine eficiency, it was the 'Tesla Turbine'-style compressor efficiency that was too low. Maybe you could use an automotive turbocharger rotor for your compressor, and a Tesla Turbine for your turbine?
Just a thought.
Dave
Hi Dave,
thanks for the thought. thats part of the problem here variable conflicting info!.
i have read up on the Tesla and have the Cairns book, now he claims the Tesla compressor is more efficient, a 6" disc stack giving something like 6bar and 100cfm at 20000rpm.
On the other hand i too have my doubts about the disc compressor, hence the prototype, which is just a couple of hours off finishing. You are right though about the std type compressor , that could be fitted instead with a Tesla power turbine. A Hybrid!.
I'll keep going for now and see how the prototype performs :D

Cheers

Nick

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Re: re: Gas (Tesla) Turbine started

Post by Nick » Tue Jul 04, 2006 8:28 pm

Johansson wrote:Hi Nick!

A very interesting project indeed, I have read about Tesla turbines and allways wondered if they could work in a gas turbine. The main difference as I remember it is that the turbine inlet nozzle design is extremely important, can a Tesla turbine work efficiently with the low combustor pressures inside a gas turbine?

Keep us updated!!!

//Anders
the simple answer is i dont know?
But im going to try anyway.
here's a film of an acrylic tesla i built running on air
Nick
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Rossco
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re: Gas (Tesla) Turbine started

Post by Rossco » Wed Jul 05, 2006 3:19 am

This is a great project! and taken on by someone with the nessacary skills and machinery will be something to certanly watch!
So, were watching! Thankyou, keep up with the info, very exiting.

The only problem that i always ran into, thinking of such things, is the need for high pressure/velocity and relativly low flow for the power turbine (tesla) and the opposite achieved by the tesla as a compressor.
This can be overcome, hopefully! or, as you mentioned a hybrid.

I have some info ive collected, and will go through it for anything of use for you. The general problem is (again stated by yourself) that its sketchy info at best, without a lot of backup, and then it goes and contradicts the next bit of info you come across!
Youre on the right path to solve this one, just do it and aquire accurate info for yourself!

In regard to efficiencies, your going to have to come up with a set of data for yourself. There is no way of telling where any particular design lies between the stated benchmarks. One will tell you that its 30%, the next 98%! A little hard to calculate anything with that accuracy or lack of!

Obviously your going for a "standard" type turbine? Discs without any fancy centre washers or earofoil spacers.
Hopefully you can get the data and combuster theory to work with this, that would be a huge step. Then, there is any amount of things to try for improvement from there.

In regard to the compressor, i assume you are thinking of "tear drop" intake holes? This is said to, in some statements "make it work as a compressor" (implying that it doesnt with round holes) and others say hugely increase efficiency.

On just one last note, i did find an interesting alternative "use" for the turbine. A hands off spinning top.
Take your stack and shaft out of the housing, sit it up on a smooth surface like a spinning top, and wind it up with some air.
Once its spinning, you can let it free, and speed it right up with well directed compressed air, and it doesnt move away from the air stream. One blast of air can make even a very badly ballenced stack spin uninterupted for a long time.
It does pump quite a bit of air tho (without a housing, in all radial directions), which must induce extra drag, so without exhast holes this would probably work for much longer.

Keep up the good work.
And make a steel one real soon so you can feed some fire into it!


Rossco
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re: Gas (Tesla) Turbine started

Post by Nick » Wed Jul 05, 2006 8:52 am

Thanks for the encouragement mate, ive got the kit but who knows beyond that :?

Anyway some interesting stuff to do.
Yes i will be machining the teardrop holes in the compressor discs and radial slots in the turbine discs.
My experience with the acylic turbines has revealed some interesting facts already. hard data is what im after. The turbine which is set up to introduce air tangentally (is that a word?) to the turbine discs and is an entirely wrong config for a compressor actually works instantly as a compressor!. i spin in up on air then remove the air feed pipe the result is a significant draft being expelled from the feed hole.
This surprised me and encouraged to move on to the test of a properly configured compressor. let me also debunk another theory whilst i at it, simple lung power is all that is required to spin the turbine up, not just move it but get it spinning and producing a low turbine wail.
This also encouraged me as it seems to indicate that reletively low pressures and volume are needed to operate the turbine, i think this is due to the very low gap losses inheirant in the Tesla design. A convention compressor would be barely able to respond to such low volume and pressure simply because the gaps between the blades are reletively large.
It occurs to me that Tesla may not have to spin up to such rpm to generate power because of this?.
Another thing im considering is a two stage compressor which using the CNC method of manufacture is not a problem, so maybe where a single
stage fails to provide sufficient pressure a two stage will do the trick?
Anyway much remains to be seen but it will be fun finding out


cheers

Nick

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re: Gas (Tesla) Turbine started

Post by Rossco » Thu Jul 06, 2006 5:08 am

Oh yes, im not saying that super high pressures or velocity is critical.

My little experiments only needed lung power. And to the ear, it sounded like incredible revs, with nothing but a drinking straw as a "nozzel".

Torque and efficiency is where low pressure higher flows will be lacking!
One thing that most of the info on these turbines agree on, is a limited efficiency range. This seems, from my reading, to be where the circumfrance of the discs starts to approch the speed of the incoming fluid steam. Under this critical speed, efficiency drops of dramaticaly.
So, to my mind, this means a definitive amount of energy per turine diameter per fluid velocity.

Now, looking back to implimentation as a gas turbine, this becomes the most critical design parameter. The turbine must remain in this efficient rev range to have enough energy for working the compressor. In turn, the compressor must be suitably sized, diameter, and disc number to load the turbine... which comes first, the chicken or the egg?

Then the combustor comes into play between the two of coarse! What pressure drop can you achieve? What flow rates are we looking at?
How much does this pressure drop load... or unload? the compressor.

Mind boggling! These turbines are going to have to be experimented with a lot.
Some things arent sitting right in my head. Such as the loading on the compressor. Its not as physicaly attached to the air stream as a conventional. How does this affect the cavitation propities?
This is proven in your note that the turbine is working somewhat as a compressor as is! It must be generating a moderate pressure difference already to force air out the inlet, when its facing the opposite direction to motion!

John, Racket, we need you to chime in here!
How much turbine experience do you have Nick? A fair bit if i remember correctly.
I think the best way to tackle this is to write a list of knowns! However short. Then, test, build and retest the tesla's to suit that.

Can you calculate/test the turbines characteristics (the tester that you have now) with different air speed/pressure/flow to govern an efficient output at reasonable input. Can a combustor be designed for the numbers?
Then building and testing the compressor could commence.

Man, theres some work cut out for you here!
I understand that you are probably planning something all similar to what im suggesting. Im just trying to think of an order that would lend itself to at least a base model, without having to optimise every step first.
There has been many people experimenting endlessly with the compressor alone.
For you project, it would be most benifficial if you could get some real numbers, from what you have, and see if they will add up to something that self sustains. This alone will be something ground breaking.

Keep it up.

Rossco
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re: Gas (Tesla) Turbine started

Post by Nick » Thu Jul 06, 2006 5:50 pm

Hi Rossco,

i have very little hands on experience with Gas Turbines really and so your thoughts and those of John and the like are absolutey welcome!.
There are so many things to consider the have their own sort of inertia! I could almost spend the rest of my life trying to second guess it all so i thought "what the heck, got to start somewhere" :-)

Im getting on with constructing the prototype n the mean time then i think i can supply you guys with some actual figures. It should be possible for me to say from these tests things like "how much air at what pressure it takes to turn the compressor to what RPM and at that stage how much air at what pressure it produces"
that will give us some "ball park" figures to play with. Hopefully by making comparisons and extrapolations what will be at least theoretically possible :-))

Ive posted below the finished bearing housing, not far to go now to finish the test prototype.
All that ask of you guys is please feel free to chime in make suggestions.

Cheers

Nick
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tesla construction 013.jpg
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Rossco
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re: Gas (Tesla) Turbine started

Post by Rossco » Sat Jul 08, 2006 1:43 am

Hey Nick,
That thing running yet???

Hey, ive been doing some more thinking on this, and decided to put a couple of things to paper... screen.

Heres a rendering of what im thinking of for the compressor.
In fact, it maybe benificial to both compressor and turbine for your aplication.
Ive "placed" it on a reflective base, to try to show both sides, and the spacers on the rivets too. (rivets/bolts, rivets were just easier to do in the rendering, and they make for great curved reflections)
Ive not done this to any scale, as it was all off the top of my head. In truth, i think the thing ended up about 400mm diameter, but, its just for show atm.

Its been done before, although as far as i know, it was very basic.
I cant see any advantage of the holes through the slots at all.
So, use the shaft as the intake, exhast.
The ones that ive seen done sofar are a little different, just using a hollow shaft with slots at the disc area.
With this application, i think that we need as much flow as possible, with the gap between the discs being the highest restriction. As this is where the energy is transfered to or from the gas.

As building and ballancing is your problem, ha, im looking at no shaft at all through the discs. This leaves a great "pickup" plenum for the discs, with even flow to each gap.
Ive always been uneasy about how the flow goes through the outer holes to the centre gaps? Although, some sort of cavitation action just may well be part of the pumping here? who knows, maybe thats the reason behind the teardroped holes?

Ok, ill let you ponder all that. I hope ive given something more than just a bundle of new questions this time!

Oh, actualy, one more question. With the turbine stack, how much advantage would you see in "sharpening" the periferal edje of the discs? Limit all possible turbulance on entering its inward spiral?

Rossco

PS, I'd be happy to send you other angles, changes or designs you would like done up for this. Youve got me thinking and inspired here!
Attachments
Stack Presentation w-plaque LARGE.zip
Telsa Turbine Disc Stack.
Central intake/exhast plenum, with bell mouth.
Outboard bearing setup.
Design and rendering by Rossco.
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re: Gas (Tesla) Turbine started

Post by Nick » Sat Jul 08, 2006 10:13 am

Beautiful rendering mate!, i doubt the real thing will look so pretty :-)


Nice design with the hollow discs but for the moment im going to stick to the central shaft with the prototype but i could test a version of the rendering by putting a hollow shaft over the central one.
I like the idea alot though, it would mean the actual shaft and bearing could be well out of the way of any hot gasses and as you say the intake flow would be greatly improved.
There is a great deal of maths for me to consider in the Cairns book so i'll be pondering that for a while yet :-()
The only draw back i can see in the design in the rendering is balancing would be more of an issue than the simple central shaft type,but not necessary to any inhibiting degree.

Im going to dive into the maths and see if i can find Cairns calculations on the air speeds and disc rpm/velocity diameter ratios etc.

Cheers

Nick

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re: Gas (Tesla) Turbine started

Post by Rossco » Sat Jul 08, 2006 1:16 pm

Hey Nick,

Im getting addicted to this!
Ive just had another play with the full GT assembly. All the housing, CC and power turbine are one part, so its not "operational" yet. Cheating a bit there.
Whats your thoughts on the layout, even though its only a rough one for now.

Ive sent you a private message btw, if you havnt seen it.

Rossco
Attachments
Tesla GT Presentation.jpg
Tesla GT assembly outline (initial layout thoughts).
Housing is blue tinted glass, just for visual of the compressor stack.
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Re: re: Gas (Tesla) Turbine started

Post by steve » Sat Jul 08, 2006 4:59 pm

Rossco wrote:
On just one last note, i did find an interesting alternative "use" for the turbine. A hands off spinning top.
Take your stack and shaft out of the housing, sit it up on a smooth surface like a spinning top, and wind it up with some air.
Once its spinning, you can let it free, and speed it right up with well directed compressed air, and it doesnt move away from the air stream. One blast of air can make even a very badly ballenced stack spin uninterupted for a long time.
It does pump quite a bit of air tho (without a housing, in all radial directions), which must induce extra drag, so without exhast holes this would probably work for much longer.
Rossco
It's funny you should mention that...
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re: Gas (Tesla) Turbine started

Post by Nick » Sat Jul 08, 2006 5:46 pm

Ha ha, cool!,
nice top!

On a more mundane subject ive been going through the Cairns book again and can find precious little hard data in it.
Its full of partial formula and extrapolated power outputs, it does things like stating a 12 disc compressor produces 6 bar and 100cfm at 9000rpm great! i think, i can get a ballpark figure if i know what size discs he's taliking about...guess what no sizes are mentioned, very frustrating!!!!!!
So there is only one thing to do and that press on with the prototype and see what happens.
I dont suppose anyone has seen any data elsewhere?

Cheers

Nick

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