help in designing a small turbine

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Zippiot
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re: help in designing a small turbine

Post by Zippiot » Wed Mar 01, 2006 7:20 am

here are a few useful links i have found, on both axial and centrifugal compressors.

http://www.swri.org/4org/d18/mechflu/pl ... adflow.htm

http://www.pcaeng.co.uk/cgi-bin/content ... i?desturbo

http://www.barber-nichols.com/products/ ... _turbines/

http://www.gepower.com/prod_serv/produc ... /pgt10.htm

(14 stage!! wicked 15k horsepower!! but its for energy not thrust...)

this site compares the 2 types in jet engine applications
http://www.frankwhittle.co.uk/centrifugal_or_axial.htm
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re: help in designing a small turbine

Post by Fricke » Wed Mar 01, 2006 8:54 am

If You are into the Micro/mini jet´s look at: http://groups.yahoo.com/group/homebuildturbines they are the ones to ask questions to... DIY GT group is more into using turbochargers like Me and Anders do...

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re: help in designing a small turbine

Post by Zippiot » Wed Mar 01, 2006 6:24 pm

thanx, diy gt's had a link to there but it said something like, an extension of this group...

i see some gt's with convergent nozzles and some with divergent nozzle...
but i dont see any with convergent-divergent...just an observation (the convergents seem to make more thrust)
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re: help in designing a small turbine

Post by Zippiot » Wed Mar 01, 2006 6:57 pm

ok, so with my access to the machine shop only going to last for another 4 weeks or so, i really want to make an axial flow turbine while i wait for my book on centrifugal is in the mail

from what i can see, it takes about 8 stages in a alrge jet to make an axial flow more efficient. in a small jet, im thinking i can fit at least 4 stages. the blades and such on the compressor will be aluminum, but at the last 2 stages i think i will make it steel just to be safe. the cone that they are placed on will be aluminum to save on weight. the compressor will be housed in a soup can (just to keep it simple, i will make a steel housing later if it actually works). then i will weld on the combustion chamber, which is a smaller soup can (!) and i will place the flameholder inside of it. how many ports will i need for the fuel? i think i can get away with just 2...

the turbine that spins up the compressor will be made from steel blades welded to a steel cylinder.

driveshaft is tool steel, screws together in the middle so it can be dismantled, also the front compressor screws on the so does the rear turbine. its all threaded so that as the turbine spins it increases the pressure keeping the whole thing threaded together.

i will need to make some flame protection for the driveshaft and bearings, i plane on sealing them inside of a cylinder filled with oil (car synthetic or the aircraft stuff, whichever keeps away the ehat better). the bearing in the rear will be totally sealed off by ceramic flame protection, or as you would call it, just some clay i threaded over it.

no nozzle for now, it can run without one right? i just need to make it work before i try to make thrust.
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re: help in designing a small turbine

Post by Zippiot » Wed Mar 01, 2006 11:07 pm

i got my basic designs drawn up, and even though designing a mini axial flow turbine goes against everything i said earlier about keeping it simple...i just gotta do something while im bored...

so my basic drawings are based around a chunky soup can as the shell. i dont have my verniers on me (left them at the shop) so im using a ruler to get the diameter measurements, dangerous cause its no where near exact...8 cm diameter outside. 5 inches tall (im just using the measurement closet to a whole number, i can convert it in my head so messing it up wont happen). the compressor will be 1 soup cna in length, the turbine and combustion chamber will also be 1 can in length. not adding a nozzle yet, so i havent calc'd how big it will be.

so the compressor will be aluminum with both aluminum and steel blades welded on. the bearings are rated to 90k rpm, but i doubt my bad engineering will get them that high... as i said before everthing will be threaded together so it tightens as the turbine spins up. issues may be aluminum threaded into steel, and the steel will be hot from the fire (i have designed in protection for the shaft and bearings but metal transfers heat pretty well...). the rear turbine will be made from a steel cylinder, with blades welded on just like the front, but this will be heavy. not only to help ballance out the weight, but to act like a flywheel and keep everything turning once spooled up. the flameholder and fuel injection might get tricky...

i am planning on 2 fuel injection points, on opposite sides of course. they will be modified ball inflation needles provided that they can withstand the heat... the combustion chamber will have 1 flameholder around each fuel injection point. i hope by flattening out the needles i can spray the fuel over a wider range, to help avoid needing more injection points.


potential problems i forsee... the aluminum front compressor getting too hot, with all the safety thing si added in it might not happen but i still fear for long term use..
bearings...the bearings i have are rated at 90k rpm, they have a 2x safety margin (thats why i got them, huge margin of safet incase i screw up and the thing actually works...) and heat to the bearings. they are going to be surrounded in oil and such, but i dont have flowing oil so i cant run it for too long.


i will lathe the completed turbines to make sure they are well ballanced, my lathe goes up to 2600 rpm, its far lower than the thing will run at but i will spin it up and slowly take off material until its nicely even.



well does it sound good? i will post a pic of my drawing later today. im sorry but i must leave for school and i cant proofread it... i just took too long typing it and lost track of the time.
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re: help in designing a small turbine

Post by Zippiot » Fri Mar 03, 2006 6:49 am

ok i got the aluminum cone for the compressor all done, well for now. i now have to drill it and "hot glue" the blades in place.

the cone is freaking awsome, it is just over 7 inche slong, but only 5 inche sof it will be inside the turbine. it is reflectively smooth, too me about 1/2 an hour of sanding of the polishing lather to get it all nice, i actually caught some of the really fine sandpaper on fire...

well now i must mark and mill out the slots for the blades, does anyone know of a good way to mark and slot a cone?

its going to be at least a 5 stage, that is 5 layers of blades on the cone and 5 on the shell, this should give me the comrpession i need for it to self sustain.

i chose aluminum b/c it is lightweight, and as mucha s i ahte it i need the thing to be lightweight incase it actually runs and i can strap it to something. the rear will be all steel, what cna i make the turbine blades out of to reduce heat exhaustion?
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Re: re: help in designing a small turbine

Post by skyfrog » Fri Mar 03, 2006 9:32 am

Zippiot wrote:its going to be at least a 5 stage, that is 5 layers of blades on the cone and 5 on the shell, this should give me the comrpession i need for it to self sustain.
Excuse me for my lame English in both reading and writing, when articles get too long I'll just skip it.

Are you refering to an axial compressor with 5 stages ? If so the best compression ratio you can get is γ = 1.175^5 = 2.24, which ratio can be done with a one stage centrifugal compressor easily. The best compression ratio they had achieved with a single centrifugal compressor was up to 8.

Welded blades are not safe in such a highly dynamic environment. Tiny cracks tends to exist and develop at the filler metal. Fatigue problem is very important you must not ignore it. I suggest that you either use centrifugal compressor or build a strong casing to prevent the grenade like axial compressors from hurting people.
Long live jet engine !
Horace
Jetbeetle

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re: help in designing a small turbine

Post by Zippiot » Fri Mar 03, 2006 5:51 pm

actually i have secured some special cement used for just this. it expands and fills in all cracks to hold something in place better than a weld. plus you can have aluminum cone and steel blades. the canister im using can take a hit, but it is a good idea to reinforce it until im sure i wont get punctured.

i just wanted to see if the axial compressor works at this size, and many of the centrifugal compressors much larger only create 2.2:1 and 16-30 pounds of thrust.

the centrifugal flow revs up easier and is more robust, but the axial flow is more efficient and has a smaller profile (but it is much longer).

i have relooked at the length of the cone and i think i can fit up to 8 stages in there.
here is my attempt at your formula, although i dont know where the 1.175 came from...

1.175^8=3.63

thats almost double the 5 stage. the cone actually sticks about an inch and a half out the front of the turbine, i might possible be able to put that to work.

this turbine will have a diameter of less than 3 inches, show me a centrifugal turbine that has that compression and that diameter (although my turbine will be considerably long)
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re: help in designing a small turbine

Post by Zippiot » Fri Mar 03, 2006 6:30 pm

ok got a few questions
1. should all the blades be the same size? the length will have to be trimmed to fit but should they all be the same width?
2. should there be the same number of blades in each stage?
3. for a 3 inch diamter how thick should the blades be?
4. should all the blades be at the same angle? what about the blades that are stationary?
5. how close should i make the tolerance between the moving blades and the stationary blades?
6. what pitch should the blades be at?

this is enough to keep me busy googleing for a day or so...
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Re: re: help in designing a small turbine

Post by Fricke » Sat Mar 04, 2006 3:21 am

Zippiot -------!!!!!!

Don´t try to glue the compressor blades to the wheel!! The result is equal to disaster... Your "tag" is that You are proud of the amount of bones broken.... bones are better broken than life broken...

I personally would buy the plans for the WASP (google) they are really cheap...

As this is the first engine Your building... Play safe...

Or go the route of DIYGT... Cheaper... And some what safer... cast iron and al is quite good to cointain explodes turbine and compressor wheels...

The 5 or what ever staged comp wheel needs to be made from billet materials... period...

//Fredrik

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re: help in designing a small turbine

Post by Zippiot » Sat Mar 04, 2006 7:06 am

you doubt my glue?

silicate anchoring cement used to fill the gaps between tiles on the space shuttle. mix in some carbon fibers and aramid threads for strength and, according to the person at nasa that got it for me, it is 5% stronger than a high speed steel piece welded together.

nice song though :)

i have ordered a few books on building the centrifugal flow turbines, but they r in the mail 4 to 6 weeks for delivery, possibly out of stock and such.


i seriosuly doubt it will work, cmon guys do you really think i am able to build an axial flow turbine this small? it is just good practise for when i get my plans for the centrifugal flow turbine.


and does anyone have an asnwer to any of my questions? or should i just wing it (i can hear you all cringing in pain!!).

plus, can you make a bomb with gasoline? the stuff isnt as strong as you seem to think.
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re: help in designing a small turbine

Post by multispool » Sat Mar 04, 2006 11:04 am

Zip,
I admire your seemingly unending enthusiasm and zest for wanting to build things and would hate to dampen it, but by the time anyone gets chance to answer one of your questions you've already asked a dozen more.

Gas turbines is a highly specialist subject and it just gets more difficult the smaller the engine size is. Your friends at nasa might be specialists in their own field but they aren't helping you if they are encouraging you to turn good metal into junk.

Will your multistage engine be completed? most unlikely
Will it work? No
Will it ever work with experimentation? No, not if it has'nt been designed properly in the first place.

How do I know this? Well, it needs a shed load of calculation just for blade shape, angles, flow calculation, material strength, mass flow etc, etc. thats why the books about gas turbine theory are so thick. and thats just scratching the surface. Machining metal is only the final stage of all this (not the first)!

I hate these tv programs and magazine articles that give a completely wrong impression that we have the knowledge to do anything, yes some of these things can be acheived sometimes by throwing a huge amount of money at it, amateurs can acheive surprising results if they are prepared to learn the theory and put in a lot of hours and dedication. But so many things are technically still way beyond our knowledge, For Instance, in hindsight, Putting a man on the moon turned out easier than finding a cure for aids, cancer etc.

All I'm saying is channel your enthusiasm into realistic attainable gaols! If you take on projects and start making them without any fundamental understanding of how they work, then all you will get is failures!

Sorry to sound like some miserable Teacher, but you did ask!

Multi,

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re: help in designing a small turbine

Post by Zippiot » Sat Mar 04, 2006 6:41 pm

dont feel bad i know it wont work. it is mostly just machining practise, something to keep me busy.

i actually have done some calculations on what angle to make the compressor cone and the exhaust turbines blade angle. im still working out the compressor's blades pitch and size, but i havent started working on shape yet...

i know it wont work, i am content with that. it is just something to keep me busy while i wait for the books to arrive. they will teach me the proper theories and such. until then, ill experiment

does anyone know of a centrifugal flow turbine that doesnt use a turbocharger's turbine/compressor? if i can locate one that doesnt require me to buy something off of ebay i may start that project.
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yay math!!

Post by Zippiot » Sun Mar 12, 2006 7:06 pm

well a very very helpful person from one of the gas turbine yahoo groups has sent me some very useful calcs to designing the blades. he also convinced me to make the blades individually and secure them to the compressor wheel (dovetail looks like a good idea).

with a 3 inch diameter the max rpm is 127.32395k if you try to keep blade tip speed under mach .8


that was fun, bring on the math!!


that is max rpm, operational rpm should be lower and actual rpm i dont expect to get very high..


well this guy has successfully made a 2 inch diameter 3 stage axial flow turbine, makes 20 pounds of thrust (!!!!!), so it does work. i will still try for the 5 stage, but i need to make a new cone and such. i expect it to be functionally making thrust by summer, and to be sustaining combustion in the next month, well see if i can make my deadline.
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re: help in designing a small turbine

Post by cudabean » Mon Mar 13, 2006 11:41 pm

does anyone know of a centrifugal flow turbine that doesnt use a turbocharger's turbine/compressor? if i can locate one that doesnt require me to buy something off of ebay i may start that project.
From your follow-up post, it sounds like you are on your way to some interesting projects. To answer your question (at least partially) Yes, the early KJ-66's used a home-made wooden centrifugal compressor. The wood was light enough to permit the housing to rotate along with the blades so there were no issues of clearance tolerances. The turbine itself, I presume was an axial flow one, but of course it would not have to be. Photos of the wooden compressor can be seen in the Kamps plans/book.

Marlin

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