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Post by madpatty on Jun 28, 2014 21:02:56 GMT -5
Thanks Racket,
What are your thoughts on Straight Diffuser blades rather than those wedge type? They are easy to fabricate in absence of mill....
Thanks Patty
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Post by racket on Jun 28, 2014 21:30:23 GMT -5
Hi Patty
Constant thickness vanes are OK , but we need wedges to provide somewhere to fasten the front cover to.
Cheers John
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Post by madpatty on Jun 28, 2014 21:47:31 GMT -5
Hi Racket,
The diffuser that i cast from aluminium is itself doubtful if i will be able to screw my compressor cover to it... It is a bit porous due to bad casting...
What about the efficiency levels of constant thickness diffuser blades (without forward curving) as compared to wedge type?? Is there any appreciable loss or gain(keeping throat area same)
Thanks Patty
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Post by racket on Jun 29, 2014 0:45:32 GMT -5
Hi Patty
Not a lot of difference , ...............theres probably more chance of lowered efficiency from either one or the other, from poor construction rather than the type differences .
Cheers John
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Post by madpatty on Jun 29, 2014 21:37:21 GMT -5
Hi Racket, Needed one suggestion...
In the case of my turbo in its original form at the compressor end, the oil slinger along with the split ring oil seal(compressor end) rotates with the seal's OD in contact with the oil seal plate's internal surface. The oil seal plate is made of some type of steel...
What my question is:- I want to make that oil seal plate as an integral part of aluminium diffuser(therefore the surface upon which that oil seal ring will make contact will be of aluminium) due to oil channeling issues.
WON'T that seal ring scratch that aluminium surface due to aluminium being softer than steel at high rpm's. And thus ruin the setup?? IS IT OK if seal ring's OD makes contact and thus rotates in the aluminium surface?
Thanks, Patty
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Post by racket on Jun 29, 2014 22:02:55 GMT -5
Hi Patty
The piston ring seal doesn't rotate, only the steel piece it fits into does .
If you're concerned about possible damage to the alloy , fit a steel tube insert into the alloy bore
Cheers John
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Post by madpatty on Jun 29, 2014 22:16:33 GMT -5
Thanks Racket....
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Post by madpatty on Jul 1, 2014 21:07:51 GMT -5
Hi Racket, The NGV section i fabricated had some flaws because of the bent vanes and poor welding... So i have decided to get the whole piece cast out of Stainless Steel.....
For that i will have to increase te thickness of NGV(atleast 5mm) so that they come out clean and complete after casting....Thus the total number of NGV will have to be reduced from 15 to say 11 or 12.(in order to keep the THROAT area constant)
Does that effect reducing the no. Of NGV keeping the theoat area constant?
Thanks. Patty
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Post by racket on Jul 1, 2014 22:52:43 GMT -5
Hi Patty
The main thing is keeping the throat area "as designed, otherwise you'll have problems , the number of vanes is less important .
Cheers John
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Post by madpatty on Jul 2, 2014 3:26:17 GMT -5
Thanks John, Here are some of the final dimensions of the flametube that are coming up according to the design:-
Inner wall of flametube length:- 70mm Outer wall:-80mm Inner diameter:-100mm Outer diameter:-133mm
Distance between inner wall of flametube and OD of shaft tunnel:- 6mm(radial)
With these dimensions i am a bit skeptical. What you say?
Thanks, Patty
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Post by racket on Jul 2, 2014 5:06:03 GMT -5
Hi Patty
The 6mm between shaft tunnel and flametube seems a bit small, have you done any flow calculations ??
Without seeing detailed drawings of the flametube and the engine its a part of , its impossible to comment on its suitability .
Cheers John
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Post by madpatty on Jul 2, 2014 7:01:16 GMT -5
Hi Racket,
All I had done till now is calculating diffuser and Turbine NGV calculations....I thought they were enough for an almost running engine.... What other flow calculations i need?
Cant really use CAD for detailed drawings because i am not much experienced with that....i will love to do any calculations regarding the engine... Just suggest me some starting point so that i can get back to you with some results....
Thanks, Patty
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Post by racket on Jul 2, 2014 18:31:15 GMT -5
Hi Patty
You need to calculate the actual volume of air per second exiting the comp diffuser and then make sure your flow areas around the flametube are sufficiently large enough for that air to flow to the flametube wall holes at relatively modest velocities..............your 6mm clearance at the shaft tunnel appears to be too tight .
Just use pencil and paper ............forget CAD :-)
Cheers John
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Post by madpatty on Jul 2, 2014 21:43:25 GMT -5
Hi Racket, If my calculations are right...
Taking overall compression efficiency of 75% and T(inlet) of 303K and overall pressure ratio of 3.0
Temperature at diffuser exit is 452K and therefore density of air at exit is 2.34 kg/m3 Everything was calculated and designed for the mass flow of 0.30kg/sec.
Area at exit of diffuser 900mm2 Therefore radial area comes out to be 900/sin(20) = 2631mm2
Hence velocity at diffuser exit is 48.72m/s......
Please point out if i am wrong anywhere...
Thanks, Patty
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Post by madpatty on Jul 3, 2014 0:46:39 GMT -5
Hi Racket,
Assuming that equal volume of air is divided to both inner and outer flametube..
Velocity in the outer annular area comes out to be 16.99 m/sec
And velocity in the inner annular area between Shaft tunnel and Inner flametube is 36.13 m/sec...
Do these figures appear correct to your intution??
Thanks, Patty
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