Do you realy need stators?
 

Hi,

I started a project to build my own smallscale Highbypass turbofan. I will be using CNC to craft the core out of steel. A thing that would simplyfy the process is if i could skip the stators.

I know the stators are used to direct flow inside the core, the question is however how much i would loose in performence if i skip these.

What do you think, would this make the engine completly useless or would it be "Ok" anyways?

The "setup" would be a larger fan in front 6 compressors and 2 HP turbines connected on a single shaft with bearings on two connectionpoints to support it.


Cheers.

I doubt you could get the engine to run at all without stator vanes - it is the combination of rotating compressor blades and fixed stators that produce the compression. Getting a miniature axial flow engine to actually run will be an extremely difficult task - the small engines I have seen have all had centrifugal compressors.

Ok thanks for the reply, I know the stators are very important i did not however know that they were so important that the engine would not function without them.

As I understand it, the stators convert the kinetic energy of the gases leaving the previous stage into higher pressure at the expense of lower speed.

AFAIK stators "straighten" the flow and prevent the air from simply going around in circles. The design, convergent/divergent, also enables kinetic energy to be transformed into pressure energy.

Good luck in your build, the tip losses as a percentage will be, I strongly suspect, simply horrendous.

Thats about it - one compressor stage is regarded as being comprised of a rotating assembly plus a stator assembly. Can I suggest you obtain a copy of the Rolls - Royce publication ' The Jet Engine' - the section on compressors will give you a better idea of how it all works - the paragraph on small engines will be illuminating.

Yes that is correct the lower speed is good this means the pressure will be higher just as the law of Bernoulli's state.

I guess i will just have to figure out a way to get some statorvanes into damn thing :).

In principle it's a simple construction.

Will probebly also have a look at that book The Jet Engine thanks for the suggestion!

If you do not want stators, you can use counter rotating blisks.

Also, CNC machining of a small blisk will not work, at acceptable rotating mass and flow characteristics, because every usable material would deform at the blades.

There is a way though, its called Electric Discharge Machining (EDM).

http://www.bladonjets.com/technology/gas-turbines/ probably builds the nicest small gas turbines. They use EDM to to machine their blisks. http://www.bladonjets.com/technology/blisk/

there are several model aircraft jet-engines on the market...a search on "youtube" will find a man in a wing-suit with these engines mounted on his boots. he launched from a drop-sircraft after "lighting up" and achieved climbing/horizontal flight whilst his fuel supply lasted.

Yves Rossi, the cross-channel "birdman" also uses these engines.

Apart from the engineering challenge, I think you are trying to re-invent the wheel.

Be advised that you will probably need some kind of airflow control system-bleed valves or variable stators- to get your engine to start,run and accelerate as axial flow engines have a comparatively small RPM operating range. Please keep us informed as to progress - you have my admiration for even attempting such a project and I wish you all the best.

Steve - RPetersson is trying to build an axial flow engine - the small turbines that are generally available including the so called Birdmans power units are centrifugal flow engines. Axial flow engines in small sizes generally do not work very well.

Quote from rpetersson:
"In principle it's a simple construction."

Please forgive a slightly frivolous comment from a non-engineer, and I realise it's an axial-flow engine you are attempting to build, but no doubt Frank Whittle would have said something similar when he was trying to obtain funding to build his first engine (not sure how his German equivalent would have phrased it)...

Lycka till!

PS: What's the melting temperature of steel, and what materials might you be using for the cans and the turbines?

The only way to retain a rotating mass inside a sleeve, (case) is with bearings connected radially to the case. Why not mount stator vanes on these required "webs"? A Twofer...

:ok:

bcgallacher - The melting temperature of steel is around 1400 degrees celcious. The only problem with steel in a jet engine would be the weight, tho this is not an issue if just keep it on my workbench :)

Aiming for a combustion tempereature of around 900 degrees, the bypass air from the front-fan will allow for some cooling on the exterior of the core also.

Lyman - Yes a web inside the core to house the bearings is one option i have looked into. But then again a web would cause alot of turbulence. So im trying to find a more streamlike design.


The goal with this project is just to get a self-sustaining HB Turbofan running. Any thrust it generates is a pure bonus.

Have a look at a Dart 7 engine. Basically an external chamber is the stator.

Garret APU's have something similar as well.

What is your reasoning to not have stators? Size, manufacturing problems,or are you trying a different design altogether.

Gas turbine engines all need a stage of compression.

mainwheel - My reasoning for not having stators is simply to make it easier to construct. I understand the need for compression. The question is if it would get enough compression without the stators to be self sustaining. There must atleast be some compression without the stators when the air goes thru multiple "compressors" into the divergent part where i will have the combustion.

I will probebly as an experiment try to build it and try to get it running without the stators first, record the result and then add the stators and record again to see what/how much improvment i got.

This sounds really interesting - good luck with it and let us know how you get on. If you're making compressor discs then presumably the stator discs would be fairly easy to make too, if you have to?

Did you ever see - I think it was a French guy - made a working scale model of a racing Ferrari - complete with fully working flat 12 engine! Absolutely amazing. The engine poppet valves were about the size of matchsticks, and it sounded like a real Ferrari when it was going.

Incredible!

You will get little if any compression without stators - a compression stage is rotor+stator, All you will do is stir the air up somewhat and I would think that all the rotating blades apart from the first row will be operating in a stalled condition. As a matter of interest how will you calculate compressor blade profiles,blade twist,chord and height? Do you know what compressor stall is? To be honest I think you are operating well outside your knowledge of axial flow compressors or you really would not have posed the question that you have.

@uplinker...IIRC he was a postman....now a full-time Engineer building models which sell for the appropriate price and he has a waiting-list so can afford to take commissions that interest him Even made the moulds for his own exact scale tyres!


@ R Petersson...Sorry, my apologies...you are indeed taking on a real challenge.

I would work on the principle that if it wasn't cost-effective, the full-size builders would not put them in! ;)

As the size goes down, the scale of your losses and juggling clearances/thermal distortion and expansion/balancing....just grow!

Good luck with this enterprise and I hope you keep us posted.