Gas (Tesla) Turbine started

[larry cottrill]

much much lower temps as well Larry?

Yes, the gas temps should be FAR lower than the pulsejet exhaust gas temperatures.

Can you sketch out what you mean?

Well, no - because I'm too ignorant of designing the turbine part. I've never really understood what they did with the turbine in relation to the SNECMA engine, for example. Does the wheel just spin across the tail end, spaced in as close as you dare to get it? Are the buckets (blades) the full height of the outlet diameter? Does a single-stage turbine work efficiently enough, or do you need multiple stages interspersed with static vanes?

All I've ever seen is the pictures of the combustor itself (by this, I mean the chamber, pipe and integral augmentor). Therefore, a lot is left to the imagination, in regard to the turbine being driven. You might think it would be pretty conventional (since dilution is part of normally-designed turbojet combustors), but I'm pretty sure that the average speed emerging from that augmentor will be a lot slower than from a conventional turbojet chamber (which, it seems to me, could be supersonic flow).

To me, the no. 1 nicest thing about inserting the augmentor tail-end design is that you isolate the pulsejet tail-end flow reversal from the region of the turbine! That should take away a lot of potential worries about what happens there.

L Cottrill

[racketmotorman]

Hi Larry
You raise some very interesting points , especially your pressure readings within the PJs tailpipe , you might need to try a water cooled pitot probe for longer duration testing .
I'd certainly agree with you about the possibility of the PJs thrust being "produced" at the combustor sections exit nozzle.
I gather the SNECMA design was for airborne use with ram air pressure in the augmentor , if this was closely "matched" for pressure/velocity with the PJs exhaust there could be a fairly efficient transfer of energy/heat between the two before entry into the turbine .
I found the freepower turbine had no decernable influence on the PJs running characteristics , either directly connected or with a gap between the tailpipe and the freepowers ductwork .
A "normal" turbine combustor has reasonably "slow" exit velocities to cutdown on losses , the gasses only speedup in the nozzle guide vanes just prior to entry into the turbine , and then only to <M 1.0 at which point they run"choked". Turbine designers try to keep away from sonic velocities because of the potentially huge losses involved , a speed of around M 0.8 - 0.85 gives a safety margin as well as good energy transfer .
The freepower inlet design I used tried to incorperate some
"augmentation" , there was provision made for a reasonably thick layer of "cold" air to flow along inside the outer wall as the ductings flow area was considerably larger than what was required purely by the area of the PJs tailpipe , and from the "colouring" of the freepowers ducting this was happening during those test runs when there was a gap between the PJ exhaust and freepower inlet .
"Normal" PJ exhaust temperatures are certainly a bit too high for a "normal" turbine to survive in for any length of time, and some form of dilution and cooling would be required for safe use .
There are a number of areas where development could be started on obtaining shaft horsepower from a PJ . I learnt a lot from my experiments , but there were probably more questions left unanswered.

The main thing to remember with any turbine experiments is to cut down the losses to a minimum, then any positives can be exploited, no matter how small they might be :-)

No matter how small the PJ , any freepower turbine will need to be "relatively large" to the casual observer , but once the maths is done , its pretty obvious why it has to be so big .

As with a freepower on a turbo jet , if its too small the engine won't work and could potentially wreck it. But if the freepower is too big all that will happen is that the shaft horsepower will be down but the gas producer will run happily, cool and safe , as long as its rpm are kept within design parameters .

Never make a freepower turbine even the smallest amount undersized .

All food for thought :-))

Cheers
John

[larry cottrill]

John -

Great information and (to me) clarification! I probably should have gone back and studied your earlier posts before pontificating.

The SNECMA engine wasn't subjected to actual ram air, supposedly - it was encased in a shell that was pressurized by the shaft-driven compressor! At least, that was the intent. (Again, I'm going from my ever-degrading memory of "what somebody said".)

Thanks!

L Cottrill

[matt512s]

Hi Nick!
I have found a new combustor design that might work for your
project. Check out US patent 6877978. If it works as advertised,
it is absurdly simple and absurdly powerful.
Best Wishes:
Matt

[Rossco]

HAHAHHA, Matt

If it works as advertised,
it is absurdly simple and absurdly powerful.

That just HAS to be a contradictory centence!
Very good tho, thanx. We need to see as many ideas that are around as possible.
I havnt had a look yet, although i surely will. Im assuming straight away that its the "valvular conduit" combustion chamber? There is many, many problems with that.
We, Nick and I, do have the available means of pulsed gas producers, so there will be some very interesting testing done hopefully in the near future.

Rossco

[Nick]

Progress update

Test prototype is nearing completion, at least in its first iteration. Pics attached.

Nick

[Nick]

it wont let me put more than one pic up?

Nick

[Nick]

last one

Nick

[skyfrog]

Good job Nick, it looks beautiful.

Have no idea of how tesla turbine works though.

[Graham C. Williams]

Dear Nick.
Another fine creation.
Does anyone know how a Tesla Turbine reacts to non-steady flow?
Do you remember when Steve attached that thin pipe to the side of his Chinese - very cold air was being ejected at some high velocity? I guess that air was being sucked into the pipe at low speed during the low-pressure part of the cycle and being ejected at the high-pressure part.
This makes me think that if you use a non-steady combustor to feed the system you may have to separate the low and high-pressure parts of the cycle at the inlet to the turbine. First to mind is a simple flap valve before the inlet to the Turbine. Air passes into the feed pipe via the valve at low pressure and is pushed into the turbine when the valve shuts at high pressure. With a bit of luck the gas temp into the turbine will also be nice and low.

Graham.

[Nick]

Hi Horace,

nice of you to say so, coming from a consumate engineer like you thats high praise indeed, thanks.

in brief, a Tesla works not with vaned rotors as in centrifugal compressors but with smooth discs set very close to each other (typically 0.6mm apart), air or the working fluid in any case passes between these discs, usually between 8 and 20 of them.
As the air passes it gives up much of its velocity to the discs surface due to the frictional drag exerted by the proximity of these discs (boundry layer effects), the air then exits from the centre of the discs through slots milled into them.
There is much written about the Tesla turbine but little hard consistant evidence of performance.
My aim is to do some experimenting and try and establish some guidelines for building a real Gas turbine based on the Tesla.

Cheers

Nick

[Nick]

Dear Nick.
Another fine creation.
Does anyone know how a Tesla Turbine reacts to non-steady flow?
Do you remember when Steve attached that thin pipe to the side of his Chinese - very cold air was being ejected at some high velocity? I guess that air was being sucked into the pipe at low speed during the low-pressure part of the cycle and being ejected at the high-pressure part.
This makes me think that if you use a non-steady combustor to feed the system you may have to separate the low and high-pressure parts of the cycle at the inlet to the turbine. First to mind is a simple flap valve before the inlet to the Turbine. Air passes into the feed pipe via the valve at low pressure and is pushed into the turbine when the valve shuts at high pressure. With a bit of luck the gas temp into the turbine will also be nice and low.
Graham.

Hi graham,

I have seen a website where the writer postualtes that a Tesla would be suitable for a PJ and as you say the experiment on steves chinese was really quite amazing. White hot CC but cold cold air coming out of the pipe, weird or what but possibly very, very useful.
Have you got your MSN live set up yet?

Cheers

Nick

[Mike Everman]

Nice work, Nick!
Everyone should know that Nick is making all of this on a small lathe and a home made(!) NC mill.
Cool stuff.

Do any of your references talk to the boundary layer thickness between disks under different conditions?

[Nick]

Hi Mike,

well in typical vague form , yes "W.M.J Cairns" states that the characteristics of the medium will affect the flow rate between the discs, so i guess he means steam will do one thing , hot gas another.?!
Mike have you got MSN live?

Nick

[Bruno Ogorelec]

Hi Mike,

well in typical vague form , yes "W.M.J Cairns" states that the characteristics of the medium will affect the flow rate between the discs, so i guess he means steam will do one thing , hot gas another.?!
Mike have you got MSN live?

Nick

He was talking about the viscosity of the medium. That's the chief parameter affecting the transfer of fluid momentum to the rotor.