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Post by racket on May 19, 2016 20:43:52 GMT -5
Hi Ryan
Now there appears to be a "difference??" between your Kamps copy and mine which is a fairly early 1995 edition , page 64.
My copy doesn't have the -9 ,...........in mine, Modulus of elasticity of steel in my edition is 210 x 10 to the 9th power N/m2, and the shaft .....I= 1.47 X 10 to the 9th power m4
LOL, .......I'd just go for a 30 mm shaft dia ;-)
Cheers John
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greazy
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Post by greazy on May 20, 2016 5:34:18 GMT -5
i finally cracked the first part if you do the proposed equation using x10^9 for shaft and modulus get the answer (about 14 digits long) then you must x10^-9 to get the 5 digit number that is the bending critical angular velocity known as ( w ) in the book.
so that parts all sweet for the comp and turb wheel however i have now found the equation for the shaft on its own should be a slightly different equation to the first one. however they have just copied the first equation again... so i cant work out the shaft w and that stops me from figuring out the entire rotor critical rpm soooo annoying. this page is riddled with cockups like decimals instead of commas and visa-versa g instead of kg missing equations ect . its 3rd edition 2005 reprinted in 2008
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Post by racket on May 21, 2016 1:07:05 GMT -5
Yep , very frustrating , you might need to find an engineering text with the "correct" formulii.
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Post by racket on May 21, 2016 1:42:41 GMT -5
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greazy
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Post by greazy on May 27, 2016 0:03:32 GMT -5
thanks john thats more helpful than the book.
quick question for you mate, I'm looking for a suitable compressor map to get some details like you suggested. what is more appropriate? one with the closest trim and physical features then scale it up or just go for the biggest inducer size? also i know trim is = ind^2 ÷ exd^2 × 100 but with the taper tip do you use the outside tip diameter or an average between tip and wheel base as the exducer size?
cheers ryan
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Post by racket on May 27, 2016 1:13:08 GMT -5
Hi Ryan
Yep , it even made sense to me :-)
Probably go for a wheel with the same physical characteristics and scale up .
I compromised and used a mid point of 157 mm for the exducer diameter in my calcs, theres a big reduction in axial tip height between 151mm dia at ~12mm down to ~10mm at 163 mm , I ended up working on a diffuser vane height of 10 mm
Cheers John
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greazy
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Post by greazy on Jun 1, 2016 16:34:11 GMT -5
closest comp map i could find its 90% smaller than the x813 but is very simmilar in its proportions the only thing i cant find is the tip height. so scaleing it up im going to work off 65,000 rpm 78% efficency 3.5pr 1.7kg/s throughput ryan , Attachments:
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Post by racket on Jun 2, 2016 5:04:48 GMT -5
Hi Ryan
I've designed on a rpm of 60,000 at a 3.5 PR with a mass flow of 3.65 lbs/sec - 1.66 Kgs/sec , hopefully I'll be able to give you some actual PR, efficiency and rpm data once I give the 12/118 engine an extended test run.
Generally a bigger compressor wheel will perform a bit better than a smaller wheel so I'm hopeful of even better efficiency than the turbo specs indicate .
Cheers John
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greazy
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Post by greazy on Jun 2, 2016 7:45:12 GMT -5
can't wait to read about a full throttle run of the fatboy. I didn't want to just copy your work so im giving it a go best i can it's comforting to know I got something close to your estimations. when you do have the real life numbers i can adjust mine if needed. I'm too buzy with the house to start making anything for a month or two anyways. so im just gathering info and parts for the time being.
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greazy
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Post by greazy on Jun 30, 2016 4:07:00 GMT -5
got a question for you john im working out the turbine dimensions and was wondering what changing the blade angle from the 30° kamps book suggests to something higher like 35-40 will effect the running of the engine. i say this because a 150mm turbine wheel will need a blade height of 46.5mm at 30 degrees and i want to shorten it for strength and to be able to craft it easier.
cheers ryan,
cheers
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greazy
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Post by greazy on Jun 30, 2016 4:17:30 GMT -5
here are my numbers so far Attachments:
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Post by racket on Jun 30, 2016 6:01:18 GMT -5
Hi Ryan
Kamps book fall short once we start getting up into higher pressure ratio engines where we don't have most of the pressure drop across the turb stage but have substantial pressure downstream .
The turbine wheel needs to power the comp , once we know the horsepower requirement of the comp , then we can workout the required gas deflection at the turbine wheel that produces that horsepower.
The gas deflection is "half" from the NGV but also "half"from the outflow angle of the wheel , so it does make a big difference going from 30 to 40 degrees .
I notice in your numbers a 3.36 Bar before and only 1.017 bar after , so you are attempting full expansion across the stage , this will "overpower" the comp unless the outflow angle is fairly large to reduce the gas deflection .
You need to draw up the velocity triangles at mid turb blade to check on gas deflection "horsepower"
I'll get back to you on this tomorrow :-)
Cheers John
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greazy
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Post by greazy on Jun 30, 2016 17:49:23 GMT -5
the input power the comp requires at 17° ambient to 3.5bar 78% = 272,425 J/kg
kamps book said it was practical to expand all the enpalthy thats why i went that path
just so you don't invest alot of effort I'm trying to design to my estimates but ultimately I want to wait for your data from a full power run before i commit to manufacturing anything but I appreciate your help mate
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Post by racket on Jun 30, 2016 19:47:06 GMT -5
Hi Ryan
Yep , with an engine thats only going to be used as a pure jet it can be convenient to have high gas speeds out of the turbine wheel , not too high as losses occur .
Will your engine only be used as a pure jet or is there the possibility that it could have a freepower attached at some stage ??
I was looking at a horsepower requirement of ~300 HP from my turbine wheel or ~82 HP/lb/sec , my apologies for working in imperial rather than SI :-)
It shouldn't take too long to come up with some rough estimates , I'll hopefully have something by this arvo .
Cheers John
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greazy
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Post by greazy on Jun 30, 2016 20:15:14 GMT -5
haha i have a converter handy ☺ yes there is definitely a possibility of a freepower attachment in the future. is there a happy medium i could aim for with decent thrust and decent shaft horsepower or will i need 2 seperate turbine wheels for each job to be done?
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