The One Man Turbofan

[monty]

Not a lot to report. Back at work...takes all my time.

I have been working on the diffuser design along with the front cover/gear-case when I can. Lots of moving parts with these two things.

Still working on the ring gear blanks. After breaking a couple home-made internal grooving tools, and ruining a couple blanks, I gave in and ordered a proper tool...

Making the replacement parts this weekend. My hands, arms, back and forehead all have burns from the hot chips flying everywhere!! I'm sure it would make a viral video...Ouch....OW....ouch OOOOOWWWW...$)$###......$*#%&#.....ouch..##%@%^!!!!!..OWOWOWOWOWO!!!!

The good news is this thing works GREAT!

Hope to get the gear blanks sent off to be cut this week, and finish up the diffuser design next weekend.

[roberto_b]

Hello Monty,
i find this forum searching for turbofan solutions, it's a lot of time i'm looking for, now i find this forum and you thanks to GTBA UK forum, i like very much your project, also if you are using some uncommon techinques, not so easy, my comliments for all this.
Now i'm involving in a turboprop project, but i'm thinking about next one, will be a turbofan, i hope you will have success on this project, so i hope replicate it.
I hear about the DGEN engine, have you design a complete 3D project of your engine ?

[monty]

Jan 27, 2019 9:23:02 GMT -5 roberto_b said:

Hello Monty,
i find this forum searching for turbofan solutions, it's a lot of time i'm looking for, now i find this forum and you thanks to GTBA UK forum, i like very much your project, also if you are using some uncommon techinques, not so easy, my comliments for all this.
Now i'm involving in a turboprop project, but i'm thinking about next one, will be a turbofan, i hope you will have success on this project, so i hope replicate it.
I hear about the DGEN engine, have you design a complete 3D project of your engine ?

Hi Roberto,

Thanks for the kind words. My thinking on this project is to be the non-aero engineer. I'm trying to incorporate as much from the automotive and consumer product/hobby world as I can. This means sacrificing efficiency on the alter of cost. I want to use as much modern tech as possible on the manufacturing side, so yes everything is modeled in 3D.

I am the polar opposite of the DGEN engine. Beauty and the beast...Hopefully it works.

Follow along to see.

Monty

[roberto_b]

Fine Monty, are you available to share the 3D design ? i would like evaluate your same task.

Roby

[monty]

Jan 28, 2019 14:24:43 GMT -5 roberto_b said:

Fine Monty, are you available to share the 3D design ? i would like evaluate your same task.

Roby

Roby,

At this time it's very much a work in progress. Not something I'm willing to share with the world other than what I post here. The turbo-fan isn't even to beta test phase. Perhaps at some point, but not yet.

It would be really interesting to see your turbo-prop project in a build thread on here!

Monty

[roberto_b]

Ok no problem, i don't want start a new project in short time, may be in timegap you will proceed with the project.
I hope you continue to keep us informed, i'm confidence the project will run, looking the pictures on this thread seem a classic radial engine with gear reduction and fan , tecnically more easy then a turbofan with second stage, like turboprop.
I'm working on Wren turboprop project, nothing of unknow or new, gas engine is ok, but now i will start 2d stage, i'm thinking the better method to realize the interstage spider, casting or 3D printing, but the material need to resist at high temeperature, not so easy...

[monty]

Put the finishing touches on the gear blanks today.

Off to the gear cutter tomorrow.

Monty

[monty]

Calculated the turbine exducer flow area in as accurate a way as I know how....

First I carefully carved a piece of card stock that would fit between the blades:

Then I traced it on graph paper, took a photo, imported it into Rhino and scaled it to the same grid size as the paper. After that I created a surface using splines and measured the area.

The magic program tells me 0.8311 sqin/passage. There are 11 total passages yielding 9.142 sqin of flow area in the exducer!!!

Needless to say I was happy with this number

[turboron]

Monty, good work. We packed the passage with RTV with an embedded bolt. We then removed the RTV once it was cured and measured the area. Now that you have an area for the exducer throat how does it compare the IGV throat area? I would think you would compare them on a total throat area basis since the number of passages is not the same. What is the ratio?

Thanks, Ron

[monty]

Jan 31, 2019 14:37:24 GMT -5 turboron said:

Monty, good work. We packed the passage with RTV with an embedded bolt. We then removed the RTV once it was cured and measured the area. Now that you have an area for the exducer throat how does it compare the IGV throat area? I would think you would compare them on a total throat area basis since the number of passages is not the same. What is the ratio?

Thanks, Ron

Ron,

Do you mean the IGV's in the diffuser?? Or the NGV for the turbine inducer?

Monty

[turboron]

Monty, sorry. I mean the turbine IGV's (NGVs).

Thanks, Ron

[monty]

Jan 31, 2019 16:41:26 GMT -5 turboron said:

Monty, sorry. I mean the turbine IGV's (NGVs).

Thanks, Ron

Ron,

That is actually what I am working on at the moment. Any recommendations?? I was just going to size the throat based on choked flow, and then make sure it isn't larger than the exducer.

Monty

[turboron]

Monty, the one data point I have for radial inflow turbines is an area ratio of NGV throat area/Exducer throat area of 0.6. My axial gas turbine experience is that choke (throat area flow is sonic) should be in the NGV. I think you could go as high as 0.9 ratio NGV/Exducer based on John's recent comment on the Allison Model 250 turbine. Boundry layers affects maybe small in a expansion. Note that you can not choke the throat unless you exceed the critical pressure ratio of around 2/1( it is 2.4 on room temperature air, I think). What do you expect your expansion ratio to be in this design?

Thanks, Ron

[monty]

Some additional info that may help some folks:

near as I can tell exducer OD is 113mm, ID is about 35mm. the triangle is about .8 in at the base, .18 or so at the tip, and about 1.6in long. I checked the dimensions in Rhino and they check out. For comparison I imported the triangle I used to estimate the Garrett wheel flow area (Cyan) and superimposed it over the Holset (green). Granted I used a much rougher estimate with the Garrett. I just measured and laid it out. I didn't take into account the actual curved shape of the throat. This creates a large discrepancy on the outer periphery as you can see below. The OD of the Holset wheel seems to be about 1.5-2 mm larger. Perhaps Andy can set me straight.

Monty

PS: I re-checked the OD of the Holset exducer. It's hard to measure with calipers. I need to put it on the lathe and use the DRO. It seems to be about 111mm maybe a bit larger. The curve of the pattern when laid out makes it appear the OD is even larger. It may be 1-1.5 mm larger but not 2.

[monty]

Jan 31, 2019 18:18:46 GMT -5 turboron said:

Monty, the one data point I have for radial inflow turbines is an area ratio of NGV throat area/Exducer throat area of 0.6. My axial gas turbine experience is that choke (throat area flow is sonic) should be in the NGV. I think you could go as high as 0.9 ratio NGV/Exducer based on John's recent comment on the Allison Model 250 turbine. Boundry layers affects maybe small in a expansion. Note that you can not choke the throat unless you exceed the critical pressure ratio of around 2/1( it is 2.4 on room temperature air, I think). What do you expect your expansion ratio to be in this design?

Thanks, Ron

Ron,

I'm shooting for max power expansion ratio of 3/1. Boundary layer always behaves better under expansion! Unless there is some kind of weird shock interactions I don't think I have to worry about boundary layers much. I'm more worried about choking the exducer before the NGV.

Monty