greazy
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Post by greazy on Feb 24, 2016 9:34:43 GMT -5
so im in the process of designing a turbojet i bought the kamps book to learn all the tricky math and its great except for one thing I have no idea how to calculate anything because i have no start point for my compressor wheel calcs (i can't fond a compressor map for it) am i missing something? i have the size of the compressor wheel i want to use, the trim and number of blades it has but thats it. I'm getting frustrated i have read the book 3 times over and still can't figure where to start. any help would be greatly appreciated
ryan
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BFTO
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Post by BFTO on Feb 24, 2016 10:52:35 GMT -5
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greazy
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Post by greazy on Feb 24, 2016 15:49:46 GMT -5
that's all helpful info but they know their expected throughput from the compressor already allowing all other calculations from there, thats the info i cant seem to find.
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Post by smithy1 on Feb 24, 2016 18:33:44 GMT -5
A lot will depend on the inducer size, exducer size and the "trim" of the wheel itself. If you can give us those numbers, we should be able to get some figures for you.
Smithy.
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greazy
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Post by greazy on Feb 24, 2016 20:12:26 GMT -5
I belive it may he the same compressor racket is using in his 118/12 engine but I can't be positive. the information I can gather is.
ind:117.5mm exd:151mm trim:61 tip height:11.99mm there is also an option for extended tapered tip diameter of 163.11mm max boost 5 bar/70 psi
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Post by smithy1 on Feb 24, 2016 20:30:12 GMT -5
Damn...that's a big impeller..! You'll be close to ~180-190lbs of static thrust with that as a pure jet.
John may be able to give you some more accurate numbers.
Smithy.
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Post by racket on Feb 24, 2016 23:34:19 GMT -5
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greazy
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Post by greazy on Feb 25, 2016 3:36:40 GMT -5
that helps a lot thanks john can i ask how you found your mass flow and pressure ratio? also is it advisable to get the extended taper tip as i understand it would give a higher PR
cheers ryan
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Post by racket on Feb 25, 2016 3:50:51 GMT -5
Hi Ryan I used a Garrett GTX 5537 comp map turbobygarrett.com/turbobygarrett/turbocharger#GTX5533R and simply made some "calculated" assumptions , which is about all we can do as turbo comp maps are for a vaneless diffuser/scroll whilst I used a vaned diffuser. Mass flow for most comps is in the 11 - 13 lbs/sq inch/minute of inducer area , with some variation due to how hard the engine is being pushed, whilst pressure ratios are a function of tip speed and exducer tip sweptback , again they'll be assumptions with where on the comp map influencing the final pressure ratio . I'm using the extended tip option as it reduces the Trim number a tad and hopefully will provide some additional benefits with regards pressure ratio and efficiency . Where are you getting the comp wheel from ?? Cheers John
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greazy
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Post by greazy on Feb 25, 2016 4:51:26 GMT -5
Kinugawa.com its the cheapest and largest compressor wheel I can find its advertised for $380. its a bit pricy but size is power.
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greazy
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Post by greazy on Feb 25, 2016 8:39:32 GMT -5
when calculating the mass flow do you take into account the center hub area as it isn't part of the compressor that dose any work. or do you use the whole inducer area blades hub and all as the intake area for calculations ? sorry for the noob questions but im determined to calculate everything on my own as to understand as much as possible before I launch into the production phase.
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Post by racket on Feb 25, 2016 14:58:09 GMT -5
Hi Ryan Yep , I use the entire inducer , the hub is only a very small percentage so not worth worrying about excluding , its the "hole in the front" that matters . Kinugawa get their comps from KTS , ktsturbobilletx.com/ its their X831 compressor wheel . Cheers John
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Post by smithy1 on Feb 25, 2016 15:38:49 GMT -5
when calculating the mass flow do you take into account the center hub area as it isn't part of the compressor that dose any work. or do you use the whole inducer area blades hub and all as the intake area for calculations ? sorry for the noob questions but im determined to calculate everything on my own as to understand as much as possible before I launch into the production phase. As John has told you...we often tend to make some "assumptions", we don't really need to be terribly accurate, mainly because there's too many variables, something +/- ~4-5% will get you up and running. TBH, we've seen some really incorrectly or strange sized/shaped combustion chambers etc which do run...rather poorly, but they still run. We tend to talk "ball park" here so as long as you're in the ball park, you should be fine. Sometimes it's not feasible or practical to make things to exact numbers, maybe due to size constraints or material availability etc...We are a bunch of DIY people and making "allowances" is what we need to do sometimes. If you follow John's advice and you won't stray far off track, he's helped most, if not all of us get our machines running at some stage or another. Cheers, Smithy.
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Post by racket on Feb 25, 2016 15:41:04 GMT -5
Hi Ryan
If you check through the KTS catalogue you'll find bigger comp wheels , but I have to ask you why do you want to suddenly go to such a large engine ??
Do you intend making the turbine wheel ??
Power consumption by the comp wheel is enormous , so turb construction will be a daunting task .
If you intend simply scaling up from the Kamps engine , it might be possible with some parts but not others unless you have a reasonable grasp on all the other component requirements .
I'm not trying to talk you out of the project , just trying to give you reality check , its a big job making a big engine :-)
Cheers John
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greazy
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Post by greazy on Feb 25, 2016 20:33:40 GMT -5
well the last jet i made took about 3 years to build from the day i got the turbo charger I'm a bit of a perfectionist and refused to do things for the sake of getting it done so it took a while and life gets in the way too. I'm assuming this more complex engine will take a while too so may as well go for a big one. I found a supplier of inconel bar stock and will be making my own turbine wheel I'll look into using plate as another option. big job but I am in no rush I want to take my time one step at a time and get it right.
i plan on having an axial turbine ceramic roller bearings and as for the lube im not sure yet between a closed circuit or the waste dump method with cooling air. I want it to be a thrust engine but also want to possibly attach a freepower turbine if it all works out well. but that would be way in the future
ryan
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