The One Man Turbofan

[racket]

Hi Monty

I was using 67,000 rpm without fan supercharge and 65,000 rpm with supercharge .

Without supercharge I had inlet velocity ~530 ft/sec and pressure of 12.5 psia but with supercharge ~ 480 ft/sec and ~14.4 psia going through ~0.08 sq ft of flow area at the inducer , inducer tip speeds a bit each side of 1,200 ft/sec , requiring inducer tip to be at ~22-24 degrees .

As for trying to guess the inducer tip angles of KTS wheels , I think the size of the superback is an indication , the X846 has 12.88 mm , the X856 only 10.08 , more superback would perhaps indicate higher stresses from higher RPM , higher RPM would indicate faster inducer tips with lower angles .

Another possible indicator is inducer to exducer annulus area ratios , if inducer area is twice the exducer area its a high pressure wheel , less than 2:1 its a low pressure wheel , the X846 has an exducer tip height of 8.8mm whereas the X856 has 11.8 mm at roughly the same inducer and exducer diameters

Cheers
John

[racket]

Hi Tony

Thats a possibiity , but that'll also change the rpm to PR ratio , and because its a single shaft engine any increase in rpm will affect the fans configuration , its also another "complication" thats best avoided if possible.

Unfortunately I haven't any clear idea what flow quantity will be able to exit the turb exducer , its only rough guesstimates at best

Cheers
John

[monty]

John,

I've crawled through these numbers up one side and down another. I think the 106mm inducer is going to be on the large side especially at altitude. I am using 66Krpm and my velocity, temp, and density numbers are close to yours. I'm leaning towards the X861. It has a 102mm inducer, the large super-back, and 9.38mm tip ht. When I scaled off one of the Garrett maps I get around a 103mm inducer for my flow rate. The 102 will be slightly small at SL static full throttle and slightly oversize at altitude. I'm getting about a 24-25 degree inlet angle at SL and 23-24 at altitude.

I wish I knew what the inlet angle on that wheel is...

The 862 and 869 are also possibilities.

Monty

[racket]

Hi Monty

The X869 seems to be the best bet I feel, >2:1 inducer : exducer area , probably based on the earlier X842 but with extended tip.

The X862 is out , no superback .

The X861 has a 9.38 mm tip height which is getting a tad large resulting in a < 2 : 1 in/out area ratio and lowish exducer air angles at higer PRs .

The X869 has a 8.10 tip height whereas Anders X846 has a 8.8 mm tip height so "closeish" in/out ratios if we take into account the differences in inducer diameters.

Perhaps shoot an email direct to KTS enquiring about the inducer tip angle before taking any further action

Cheers
John

[monty]

Feb 6, 2019 19:56:54 GMT -5 racket said:

Hi Monty

The X869 seems to be the best bet I feel, >2:1 inducer : exducer area , probably based on the earlier X842 but with extended tip.

The X862 is out , no superback .

The X861 has a 9.38 mm tip height which is getting a tad large resulting in a < 2 : 1 in/out area ratio and lowish exducer air angles at higer PRs .

The X869 has a 8.10 tip height whereas Anders X846 has a 8.8 mm tip height so "closeish" in/out ratios if we take into account the differences in inducer diameters.

Perhaps shoot an email direct to KTS enquiring about the inducer tip angle before taking any further action

Cheers
John

John,

I have no idea how I missed the 862 not having a superback! Just looking at the inlet and outlet I guess..

If I had my way I'd like an inducer designed to flow the correct amount with proper angles and a larger tip height to have more diffusion in the wheel so the static diffuser doesn't have to work so hard. Unfortunately none of these wheels seem to be made that way. A larger tip ht is going to mean the wheel is designed to be low pressure ratio and high flow. Just going to have to make the best of it. The other possibility is the 892. Unfortunately, all of these are more expensive!

I assumed 5% BL blockage, is that close to your number?

I'm waiting to hear back from KTS...

Monty

[racket]

Hi Monty

Our problem is that these are turbocharger comp wheels with hugely varying flow requirements rather than gas turbine ones which would have narrower ones.

A larger tip height will produce lower exit angles which can then cause problems with diffuser design, longer flow paths increase losses :-( .....................the 106 mm inducered Garrett GT6041 has ~12 mm tip height, but the vaneless diffuser has a "pinch" outboard of the wheel to reduce the axial height of the passageway to ~9mm to maintain/increase radial velocity to prevent a long flow path with large losses at the higher PRs .

Heres a pic of the diffuser from a 170 lb thrust RC engine


You'll note very little vaneless space between wheel and diffuser tip , and a very short "high tangent angle" diffuser.

Cheers
John

[Chuks]

hi John,

but cant KTS or any of those machine shop that makes compressor wheels customize these wheels for us? just thinking...

hi Monty,

don't really know what you are aiming at but maybe you should take a look at the X851 wheel...100mm inducer,
I will be using that in my turbo shaft build.
Cheers
Chuks

[monty]

Hi Chucks,

I looked at that one, but 100mm is starting to be on the small side for my current full power mass flow target. All of this depends on what the turbine exducer can do...and that is a question mark at the moment. That is why I don't want to spend the money on a custom wheel. If I knew that number for sure and could design a wheel specifically matched to my engine I would. Right now though I just want to get a running prototype to take some measurements.

It would be nice if we could all post the inducer tip angles of the wheels we have in our possession and start a database!

So far I know the X856 is 30 degrees.

Monty

[dieselguy86]

Hi Monty,

I deal alot with KTS, when they first started they use to do one-off customs. However now that they have been establish and have a large market, they no longer make one-off’s unless you order a quantity of 5 wheels, plus a $100 design fee.

My suggestion would be to find a wheel with the right exducer you need and larger inducer than you need, then go to a machine shop and have them trim the inducer/radius to your specs. Alot of places here do it, but im also in the heart of tractor-pulling country. As far as blade angles go, probably gonna be “slim-pickings”.

-Joe

[monty]

Feb 8, 2019 13:46:16 GMT -5 dieselguy86 said:

Hi Monty,

I deal alot with KTS, when they first started they use to do one-off customs. However now that they have been establish and have a large market, they no longer make one-off’s unless you order a quantity of 5 wheels, plus a $100 design fee.

My suggestion would be to find a wheel with the right exducer you need and larger inducer than you need, then go to a machine shop and have them trim the inducer/radius to your specs. Alot of places here do it, but im also in the heart of tractor-pulling country. As far as blade angles go, probably gonna be “slim-pickings”.

-Joe

Hey Joe,

I thought about  that. I've got a lathe I can use to do that. Unfortunately when I ran the numbers, the trim would be excessive to make the angles work. Then the flow area was too small. Unless the inducer is in the ballpark to start with, trimming isn't going to fix a large mismatch. It might allow me to fine tune things, a degree or two, but not 5 or 6.

Monty

[racket]

Hi Monty

You must have gotten the "odd man out" , the X846 , X 831 and X 858 all have inducers around that 22-24 degree area .

106 mm inducers is a "class" for drag racing , so maybe yours is a "special" to get as much airflow through that sized hole as possible irrespective of any efficiency concerns which can be "acceptable" with a turbocharger setup

Cheers
John

[racket]

Hi Joe

As you're in tractor pulling territory, whats your thoughts on powering those large compressor wheels ??

I've searched around the Net but theres not much "technical" info available other than peak boost levels , but those huge boost levels need massive amounts of horsepower especially as the efficiency levels must be getting kinda poor at the required tip speeds.

Initially when I started building the 12/118 I did some numbers for a higher pressure ratio of ~4.5-5:1 so as to "lower" the NGV angle and get more gas deflection as well as mass flow through the restricted flow area ,but it was going to require something around 500 HP from the turb wheel to drive the comp , a horsepower level I felt was beyond the turb , but in the last year or so I've been having second thoughts because of those "pullin" configurations and started exploring options a little more earnestly since Monty was able to help me out with the G Trim turb wheel .

Your thoughts would be appreciated .

Cheers
John

[jetric]

    Hi Monty,

   Have you thought about using IGVs before the comp inducer to change the angle of the relative airflow into the inducer?


 Rich.

Feb 8, 2019 16:59:37 GMT -5 monty said:

Feb 8, 2019 13:46:16 GMT -5 dieselguy86 said:

Hi Monty,

I deal alot with KTS, when they first started they use to do one-off customs. However now that they have been establish and have a large market, they no longer make one-off’s unless you order a quantity of 5 wheels, plus a $100 design fee.

My suggestion would be to find a wheel with the right exducer you need and larger inducer than you need, then go to a machine shop and have them trim the inducer/radius to your specs. Alot of places here do it, but im also in the heart of tractor-pulling country. As far as blade angles go, probably gonna be “slim-pickings”.

-Joe

Hey Joe,

I thought about  that. I've got a lathe I can use to do that. Unfortunately when I ran the numbers, the trim would be excessive to make the angles work. Then the flow area was too small. Unless the inducer is in the ballpark to start with, trimming isn't going to fix a large mismatch. It might allow me to fine tune things, a degree or two, but not 5 or 6.

Monty

[monty]

Feb 8, 2019 18:21:25 GMT -5 jetric said:

    Hi Monty,

   Have you thought about using IGVs before the comp inducer to change the angle of the relative airflow into the inducer?


 Rich.

Rich,

I don't really have room for IGV's. The support struts for the gear case take up most of the transition duct. And unfortunately, like John pointed out, using IGV alters the work/rpm output and would mean changing the fan since this is a single shaft engine. Not something I really want to do. This isn't a show stopper, I just need to find the right wheel. I think I just happened to pick the wrong one because I was trying to find a larger exit ht on the exducer.

Monty

[dieselguy86]

Hi John,

My thoughts? Honestly i dont know how they do it. Most pullers are farmers that buy everything as assemblies, then just assemble it. They’ll buy a built engine from X company, Turbo comes from Y, frame from Z etc. the companys that build the turbos arent giving their secrets anytime soon. Very little is done by math, most of it is trial and error, build it, run it. I know they are getting so much power out of the turbines they are making larger quills, and keying them to keep the comp from slipping on the shaft.

While im being honest, you guys are much, MUCH smarter than me! Im learning the equations, and slowly climbing the ladder of “turbo smarts”. I WISH i was at the level you guys are to be able to follow the math and understand it all alot better.

Anyways, i do have some numbers for you if that helps. Good friend of mine pulls and has a data logger on his puller. I believe his charger is based off the Hx83, with a 4.5” inducer they are making 120psi at 100k rpms. I believe tit’s are around the 1,800°f mark. Ambient air temp during pulling season is usually between 75°-85°f, ~800’ elevation. I know they spray water into the comp to mostly control its speed. At 105k rpm they know it’ll only last 2-3 pulls before she lets go. I asked about airflow, and he said he doesnt have that working yet, so unfortunately its a guess.

Wish i could be of more help you guys are a huge inspiration!