Contemplating an HX82 Turbojet

[finiteparts]

Monty,

Here is a link to the photos of my GTCP36 turbine rotor....it a bit rougher than yours, but I think it bares a very good resemblance to what you have there.

jetandturbineowners.proboards.com/post/11384/thread

What book were you using?   That seems like a giant miss for any turbomachinery book.

I work with a bunch of ex-Pratt guys.   On of the turbine aero chief engineers was telling me about a small radial turbine that he tested while there that was at the time (and may still be) the highest specific power radial turbines.   He couldn't tell me anything other than what was in the AIAA paper, but it was still cool talking shop with him about small radial turbines.

- Chris

[monty]

I've been through all my numbers, and some interesting things are showing up. I find the best performance when nothing is choked, but the exducer is "close" The turbocharger turbine likes more RPM. Helps the inlet vectors out. The turbine solidity and the required work and mass flow fix this number fairly well. Basically I just adjust the NGV angle to an achievable area/angle to meet the requirements. Exducer conditions are set for zero swirl.

I'm currently working on theoretical compressor to match. I'm using some info in Hill and Peterson mechanics and thermodynamics of propulsion. This is my go to text. All the newer texts are too complicated for my use. I don't have enough data to determine all the loss mechanisms they include. I do know rough stage efficiencies, and H&P have straightforward derivations with stage efficiencies and basic loss mechanisms. They have a guide for tip speed ratio vs Pressure ratio. For our pressure ratios, the diameters recommended are quite a bit smaller than the wheel I have. I'm in the process of calculating the "ideal" tip ht. I'll try to match the numbers to something from the KTS catalog....we'll see.

[racket]

Hi Monty

Your calcs are getting closer to my real world ............interesting , so a ~"50/50" split of pressure drop , like an axial stage .

Zero swirl in the exhaust is pretty much what I was getting when I had the "flag" installed .

If you can't find one in the KTS catalogue ..........it ain't made :-)

Cheers
John

[monty]

John,

The aircraft comps all tend towards smaller inducers. The inlet flow is faster and the angles are steep, like 40-45 degrees. This increases the diameter difference so you get more pressure rise for a smaller diameter wheel. Makes sense, smallest wheel, largest flow, most Delta P. There is ONE wheel that is close to the right numbers, but it's a custom reverse rotation. Probably first stage in a multi-turbo high perf diesel setup. The inlet flows are getting close to choke and the diffuser is a nightmare. RPM is up around 74krpm, makes the turbine happy, if it's not too much structurally. Don't know what RPM these turbines are good for. Guess I need to look at that too...

Monty

[racket]

Hi Monty

74 K is getting pretty high , 1640 ft/sec , might need to keep temps down a tad .

The TF15 comp wheel that came with the CHRA has that nice combination of a very low 41 Trim, 10+10 blades with a 33 deg inducer tip , high inflow speeds but only a Mach 1.2 relative speed , exducer backsweep only 70 degrees so definitely a good high pressure wheel , inducer to exducer area ratio ~2:1 , exducer passage height 7.5mm at 170 mm dia , 108.5 mm inducer , ..................lotsa superback at 12mm


Cheers
John

[monty]

John,

I'm still working with the Holset wheel. I have it, and I haven't heard back from the TF15 guys. I really want to confirm my numbers are "close". I'm going to follow the numbers with this wheel and see where it gets me. I'll make sure an put a pressure tap between the Comp and diffuser. Hopefully I can make some sense of things.

Monty

[monty]

I ordered a comp wheel. It's a little smaller than what most are using. However, it matches theory. I can't do much more without being able to measure the actual inducer tip angle. I "should" be able to adjust the mass flow, rpm and pressure ratio to match it and turbine pretty well. I backed off the rpm. I sized it for 64-68krpm. The numbers say about 200 lbs of thrust. Depending on the inducer angle it could do more, or less. The one thing it should do is test the ideas I have about wheel matching. For once, I'm hoping for a HUGE inlet angle....instead of praying for a smaller one that never turns out. Why oh why can't KTS post the inducer inlet tip angle!!?? It looks relatively huge in the pictures so there's hope. I should be able vary the NGV to work with the stock Holset turbine with comp inducer angles between 30-40 deg. Target PR is 5.

[racket]

Hi Monty

If the inducer tip is too low maybe install an IGV with "reverse" angle to rotation .

What wheel have you ordered ??

Cheers
John

[monty]

John,

I went with one a little larger than I wanted. The X863 is the one I wound up settling on. I'm looking at a couple smaller ones to compare results. I'm going to make the diffuser and front cover easily interchangeable on this engine.

I only want enough tip speed to generate the pressure ratio I'm after. Anything larger just means more inefficiencies. Smaller diameter allows more room for longer more efficient diffuser channels. I also want an inducer "just" matched to the flow at that speed. As small as I can get to maximize the tip speed ratio. I WANT a large inducer tip angle. If I could get a smaller inducer with around a 40-45 degree tip angle, that would be ideal. At least to test things.

I'm viewing this engine as a learning exercise, and model validation. I'll also get some good data on the turbine limits. It may not do what I want....but I'll learn something either way.

Monty

[monty]

John,

Another thing I'm wanting to explore is higher sustained pressure ratios and cooling the comp wheel. I'm going to do the bleed air cooler thing. You wouldn't happen to have a link to that ABB paper would you??

Monty

[racket]

Hi Monty

This one www.semanticscholar.org/paper/Single-Stage-High-Pressure-Turbocharging-Gwehenberger-Thiele/eacd43d99e9b5c0a935a5472c5b947f98933d3a6

And another that looks interesting ;-)

library.e.abb.com/public/8922d10142e74e3e84f1d310a91f9864/56-61%20m9052_EN_72dpi.pdf?x-sign=lOAz4nEynTOzju6f9hddewN6ln3HjXaU8Yi+f6b5VKzdsZVA12Ui+T2lGTlWWI4C

ABB is the place to look for new ideas when we get into these higher PRs :-)

Cheers
John

[monty]

Thanks John.

There is going to be an upper limit to useful PR. I'm not sure where it is. It will of course depend on the pressure drop across the combustion liner. Might be able to play some games with higher PR and better mixing in the combustion can...But to figure out the upper limit we need a turbine map. Once the turbine exducer throat chokes, increasing PR = increasing mass flow until the axial exit velocity hits M1. The relative frame M# will be greater than 1. Can't increase PR after axial Mach=1. I'm going to design for choked exducer throat at max rpm standard day. I'll put a stagnation pressure/temp probe in the exit flow. Should allow us to at least learn how close we are and guesstimate if we might squeeze a little more through. The X863 dia should be big enough to explore some higher pressure ratios. Whether the inducer is right for it remains to be seen. It might be, since it is a tad larger diameter than ideal. IGV's might allow exploring this a bit.

Holset info says the HX82 can support up to 1.5 kg/s. I've designed for that, but Scott's engine seems to be doing a bit more..so there may be some room to grow with higher PR. I think 5% BL blockage is a good number for the turbine. Seems to match up nicely with results.

Monty

[racket]

Hi Monty

Now thats an interesting thought .................compressor stage designs like to have inducer throat choking and diffuser throat choking occurring at the same time , why wouldn't the turbine stage .

The ABB comp wheels are just comp wheels , so their high PRs are designed with the matching diffuser throats to get those 80% efficiencies at >5 :1 PRs , theres a penalty at lower "off design" PRs by the looks of their maps .

Getting the comp stage to work at its absolute best is the most important thing , less pressure drop required across the turb stage provides more flexibility , its a juggling act for sure

You'll have no problems getting your 1.5 kgs/sec at the PR you intend using.

Cheers
John

[monty]

John,

I don't think these turbocharger turbines are designed for a choked NGV. At least I can't make the numbers work for that condition. The incidence angle entering the turbine winds up way too shallow. It should be somewhere between 20-40 degrees. Whenever I set the NGV to choked condition the angle is too low for efficient operation. I actually get better numbers the lower I go on M#. Of course you reach a limit where the NGV angle is too shallow. 

Could be I'm doing something wrong.

Monty

[racket]

Hi Monty

Could you Post some "numbers" so that I can have a look to see how they compare with those I did for Anders JU-02 engine .

Cheers
John