A small gas turbine with Axial Flow Compressor!

[racketmotorman]

Hi Arman
It won't make any difference how much clearance you leave . Your "compressor" will not work , there are just too many things wrong with it . All you've got is a series of "fans" similar to what you'd find on any electric motor , they'll move air very inefficiently , but won't build the pressures required in a gas turbine for the thermodynamics to work .
The first time you "light a fire" in her , your"compressor" will simply stop working and flames will spew forth from it :-((
Get the books and read them , you're currently heading down a dead end path.
Cheers
John

[gundamnitpete]

you can use steel for your turbine wheel. cut and bend will work.


http://gtba.co.uk/engine_designs/schreckling.htm

here is one of the first gas turbine designs available to a home builder, and it's compressor was made of plywood and reinforced with carbon fiber. and it ran.


http://www.geetel.net/~turbojer/gallery7.htm

here's a guy who built a turbine, making the wheel and NGV assembly of steel, and the thing ran just fine.

you prolly don't need it to be cast of laser cut, unless your looking for +50 lbs thrust and super high RPM's and compression ratios.



http://www.pw.utc.com/presskit/images/f ... ay_low.jpg


here's a cross section of the F119 turbine by pratt and whitney, which powers the F/A-22 raptor.


notice how they reduce the amount of space inside the engine (using something like "cones") as the air gets closer to the combustion chamber?? this is what causes the most compression, the compressor blades force the air threw the smaller spaces, and thus, compresses them.


you'll need to built something like that to get a decent compression ratio, IMHO.

best of luck to you

[Arman_awn]

Hi Arman
It won't make any difference how much clearance you leave . Your "compressor" will not work , there are just too many things wrong with it . All you've got is a series of "fans" similar to what you'd find on any electric motor , they'll move air very inefficiently , but won't build the pressures required in a gas turbine for the thermodynamics to work .
The first time you "light a fire" in her , your"compressor" will simply stop working and flames will spew forth from it :-((
Get the books and read them , you're currently heading down a dead end path.
Cheers
John

Hello John,
I'm really upset why don't you read the posts carefully. I mentioned that I'm building the compressor wheels wheels on a lathe this time with a lot of precision, every stage follows a logical order from the aspect of the number of the blades, angles, and almost everything. Sufficient mathematcis are also done to determine what pressure ratio the compressor produces(about 4:1). The pictures you see are my old compressor wheels, They were just some aluminum sheets that were cut and easily shaped by hand, they were just some models of the real compressor.
You even didn't notice to my question. I want to know how much space should be available between the the tip of the compressor blades and the inner casing of the compressor. Because you know that if you leave too much space, the compression will be lost.

I also want to know how building the stators should be done.

[gundamnitpete, Thanks for your information. I want to use 7mm thick steel for the turbine, is it good enogh?]

Thanks,


Arman.

[Anders Troberg]

I think 7mm will be enough, especially with a modest 1:4 ratio. If that fails, other things will fail first.

[Arman_awn]

Hello everyone,
The compression ratio of 4:1 was just a typing mistake! I expect this 6-stage axial flow compressor to produce a compression ratio of 10 to 14:1.

Still no one has answered my question:
How much clearence should be available between the tip of the compressor blades and the inner casing of the compressor. I have considered about 1mm, that's why the compression ratio will be lost if there is more space available.

The other thing I wanna talk about is: I wanna get a 10cm*10cm steel sheet, make it circular on a lathe and cut the blades(the number of blades is 21, the entrance angle is 80 degrees and the exit angle is 34) .The hub is about 7mm thick and the blades are 3mm thick. In your opinion, will such a turbine work with this engine?

Will you please help me to design the stators and the NGV?

Thanks,


Arman.

[gundamnitpete]

i think you'll find, that getting a homebuilt turbine to RUN isn't superbly hard for someone with a good head on thier shoulders.


getting it to produce useable thrust, or be small and light enough to power a small plane, is the hard part.

i'd google the clearance..... others have built axial flow compressor turbines

http://gtba.co.uk/gallery/axial/2.html

[Arman_awn]

in this stage, I see myself almost successful, Even though you are so disappointing people.
I expect this engine to produce about 40 lbs of thrust. Do not hesitate, it can.

[gundamnitpete]

in this stage, I see myself almost successful, Even though you are so disappointing people.
I expect this engine to produce about 40 lbs of thrust. Do not hesitate, it can.

no offense my friend, but 40 Lbs of thrust is quite a claim for anyone, esp. if it's your first turbine built, and the combustion chamber, NGV, and turbine(s) aren't fully designed yet.



never the less, i wish you luck, and hope you see you post video once you've completed the engine, regardless of thrust output :)

[racketmotorman]

Hi Arman
The industry recognised pressure ratio per stage for an expertly crafted axial compressor running at design tip speeds is ~1.2:1 , therefore your 6 stages would only produce 1.2 X 1.2 X1.2 X1.2 X1.2 X1.2 =~3:1 pressure ratio, no where near your claimed 10 or 14:1 , get real man !!
Stop buggerising around , you don't have the faintest idea what you're talking about , go read some books .
My last email to you on this subject
Cheers
John

[Arman_awn]

Hi John,

So the typing mistake was something right. the compression ratio aslo depends on the RPM, in what rpm the pressure rise per stage is 1.2?

[Gripen]

do u have any calculations?? if so why don´t u post them so we can se how u thinking?? cos i don`t get it

[Zippiot]

The entrance and exit ratios are sound, but I see little compression from a cone section. All the pics of my 3 stage axial are on my other computer I'll have them off soon, also on there I have some great calculations that might help out. My 3 stage made about 17 pounds of thust, even though it didnt make much compression and only spun around 63k rpm. A friend over the internet helped me design and build it, his axial flow 3 stage made 23 pounds...and was smaller than mine!!!

[racketmotorman]

Hi Zippiot
I'd like to see them when you can post on site .
Cheers
John

[Zippiot]

Here are a few pics of the mini axial flow a friend of mine made. There are more pics available in the yahoo group homebuildturbines.

Mine is similar, larger diameter and less "presicely" machined. Mine is a wheel full of casted aluminum blades, the turbine was machined steel. Nothing special...that is why it failed after about 3 hours of use. The rear melted away and the turbine slowly spun itself down...Once I get a lathe and mill I will repair the dammage, but that seems years off now.

Remember that is not my jet, mine is similar but not nearly as nice. Especially now as most of it has melted away...

[Zippiot]

If you look closely you see many difference between each stage, that is why it actually works at that sall size. It took me what seems like a year of math just to decide the tiny differences between each stage.

The fail point in these axial flows should be the compressor [aluminum]. They have a low low max rpm limit, amny r/c sized jets can spin at 160k rpm (right?) well these are drastically limited, as the rotor tip must be kept below mach 0.8
The max rpm of my 3 incher is just over 60k rpm, a 2.5 would be in the area of 78k rpm (estimates I can do the math if I need to).

A simplified way to determine max rpm in an axial flow is


642240/(2*PI*R) that will give rpm at mach 0.8 tip speed. Feel free to correct my math if it is incorrect.

Also, as stated earlier a way to determine compression

1.175^n n=number of stages. It is just a rough number, but even though lower compression, axials "seem" to make buttloads of power.