The humble beginnings of something BIG; JU-03!

[richardm]

Car CVT transmission are quite common I Had one on my 2013 Honda Accord You would have the transmission gears dirrential etc allin one package You could connect it to your engine with a thooted belt

www.youtube.com/watch?v=PQHVLH8jVc8

[Johansson]

I´ll check it out.

[Johansson]

No big update, but I finished welding the diffusor housing today.



It would look nice if I could skip the comp cover and just run a sealing strip around the exducer rim.



/Anders

[richardm]

Nice welds ! I like your workbench too! As crowded as mine so I dont feel alone ...
Are you gonna give it a gentle spin ( electric motor quick set up ) and sit behind to feel the breeze?

[Johansson]

A cluttered desk means a cluttered mind, an empty desk means......

Nah, I don´t have anything suitable for spinning it. It will have to wait until it pulls itself around.

[finiteparts]

I did an estimate of the burst speed for your disk.   I have quite a few assumptions in the hand calcs such as:

   - the ultimate tensile strength is assuming the bulk disk temperature is below 750F

       -the welded on hub does not contribute significantly to the hoop stress carrying ability of the disk (if the weld is not a certified, full penetration weld, there will be a "build-in" crack that depending on it's size can reduce load capability of the weld significantly) 

       - The bolt holes for the blade have been ignored, they will produce significant stress concentrations and the local peak stresses could exceed the material capability...can look at those separately in the future.

      - For the first set of data, I ignored the pull loads of the bolts and blades, to isolate the ability of the disk itself.

The estimate is that the burst speed of the S355 disk by itself, would be around 16,600 rpm.   So the 10krpm would have a roughly 40% margin to a calculated burst speed of a simple flat disk matching your dimensions.

Now, when I include the pull loads of the bolts and blades, things go down fast.   At 10,000 rpm, you have a pull load of 207,230 lbf on the disk!!!!  The calculated burst speed is now around 11,500 rpm, but by the time you hit around 7500 to 8000 rpm, you will be yielding the disk and thus likely the blades will rub.   But at this speed, with a typical stress concentration factor (Kt), the bolt holes would have exceeded the ultimate tensile strength.   

So if I determine the speed at which the bolt holes will be at 0.2% Yield stress, then it will bring the speed capability of the system down to just under 6000 rpm.   Above this speed, you will be elongating the bolt holes and again, you will likely rub first, but you could experience a blade out condition still, because I haven't considered any bending that could happen in the bolts due to the load acting on only one side.

Thus, there may be a chance to get to 4000-5000 rpm without an incident.  There is a lot of assumptions in these calculations and as such, the results must have some tolerance bands associated with them...and without better material data, surface roughness at the bore, x-ray'ed to make sure there are no inclusions or voids, etc....these values are just order of magnitude approximations.

I hope that is somewhat helpful,

Chris

[finiteparts]

By the way, you might need to think how you are going to purge the forward and aft disk cavities.    And also, how much air will be needed to cool the disk.   

The S355 material strength capability falls away very rapidly after you hit about 550-600 C.   The yield and burst speeds will fall in a similar fashion.

- Chris

[Johansson]

Chris, this is very helpful indeed. Thanks a lot for taking your time to make calcs and explain how an, in an uneducated mind, insignificant thing like holes around the disc outer edge can become a major issue at higher rotational speeds.

I´ll use plenty of bleed air behind the discs to keep them cool.

The segmented turbine blades are a mechanical challenge to fit to the disc properly, but they are very practical for production.

If I would keep them for mk2 and instead of a single disc use two steel/stainless discs back to back with the blades in between like a sandwich, how much would that improve things? If I would pick a better material for the discs (no inconel but the best "available" material) and silver solder the hub sections to the disc sides.

This means that I get a better working condition for the blade bolts, since they have twice the shearing points with DISC/BLADE/DISC instead of just DISC/BLADE.

How close to 10k would this take me before things start to stretch too much?

/Anders

[wannabebuilderuk]

Should just pop this in lol www.instagram.com/reel/C3a4IiQvCxy/?igsh=MTMyZHA1YnVuZHNwag==

[richardm]

Curious about that thing max rpm..

[racket]

www.maritimeinformed.com/man-energy-solutions-man-tca77-prime-mover-technical-details.html

14,200 rpm , diameter probably ~24 -30 inch depending on required boost

[Johansson]

Today I made the blade twisting jig that I have been thinking about for some time, using a vice and a pair of pliers is not the way to go if I want to make 40 identical blades.



A simple setup that should produce repeatable results, I heat the blade root with a propane torch to get the twist as close to the root as possible.



I used the test blade section to find the right setting for a 30 degree twist.



Some heat and gentle twisting later.



This is the result. I am a bit undecided about any further profiling, I´d lose a little weight on the blades but it would be interesting to try them as they are first just to see how they perform.



Cheers!
/Anders

[Johansson]

What is the best suited M6 bolt material for fastening the blades?

12.9? A4? Titanium?

[richardm]

Titanium would be 3 to 4 times stronger than stainless and lighter.

[Johansson]

I tried some Google-Fu on bolt single shear strength but didn´t find any site comparing different materials, and the rotational forces make weight a big factor for me as well.