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Post by racket on Nov 26, 2023 16:05:55 GMT -5
Rotor dropped off for balancing :-)
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Post by andym on Nov 29, 2023 16:39:10 GMT -5
Rotor dropped off for balancing :-) Soon start up
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Post by racket on Dec 5, 2023 18:58:24 GMT -5
Rotor back home :-)
Test run before Christmas
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Post by andym on Dec 6, 2023 5:25:52 GMT -5
Rotor dropped off for balancing :-) Time to play.... when its a liitle cooler
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Post by racket on Dec 6, 2023 17:29:04 GMT -5
Hi Andy
Rotor back in engine , just painting the black/white snout for the tach :-)
Cheers John
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Post by racket on Dec 12, 2023 3:09:18 GMT -5
Hi Guys
Test run completed , engine still OK :-)
Running cooler but thrust down , I might have reduced the NGV throats a tad too much as there was chuffing like a steam train at lower P2s with lotsa air going in the wrong direction :-(
Will look at vids and numbers tomorrow
Cheers John
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Post by racket on Dec 12, 2023 16:53:40 GMT -5
Hi Guys Video of yesterdays test run youtu.be/ui5TW2mqRcACool running , low P4t and low thrust. Good spoolup though :-) Cheers John
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Post by racket on Dec 12, 2023 17:26:38 GMT -5
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Post by racket on Dec 12, 2023 17:31:41 GMT -5
Thrust youtu.be/i724mpfv60MWay way down on previous runs :-( with tighter NGV throats which are now choking , mass flow reduced and combined with a now "oversized"jet nozzle the P4t is lower along with the temps so lower velocity produced .
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praendy2203
Veteran Member
Joined: August 2020
Posts: 178
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Post by praendy2203 on Dec 13, 2023 1:58:28 GMT -5
Moin John,
At least your engine is running again and still alive.😊
Now you have higher temps with lower P2 and lower temps with high P2. That reminds me on my engine before mods.
I think thats a better start to work with, like opposite values😉
Do you have m chance to open up the ngv, without much work?
Are the vanes trailing edge only bended, or welded?
Andy
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Post by racket on Dec 13, 2023 3:28:46 GMT -5
Hi Andy
The trailing last half of the vanes isn't welded so able to be bent a bit to open up the throats , previously I was running 11mm throats now its only 9.2mm , so maybe a 10mm throat would be a good compromise .
The amount of air getting blown out of the surge slot was very high, the red manometer was indicating 470mm of water head of pressure , this is twice what I had previously, ideally I'd like a maximum of 100 mm of water head at the surge slot
Also it was possible to feel the air being forced back out of the inducer at low P2 pressures , the comp was well into surge .
It wasn't an ideal afternoon for testing with 28 deg C ambient temp with high humidity , but at least the numbers are sort of understandable .
With 0,5 Bar of P4t at ~900 deg K we'd expect a temp drop of ~78 deg thru the jet nozzle producing a gas velocity of ~1400 ft/sec , density at 900 minus 78 = 822K would be ~~37.3 cu ft/lb , jet nozzle 113 mm - 4.448"dia , 15.54 sq ins - 0.1079 sq ft , 0.1079 X 1400 = ~150 cubic ft/sec , 150/37.3 = 4.02 lbs/sec , right on my designed flow , but the thrust level is too low for that flow :-(
165 lbs of thrust from 1400 ft/sec only requires~3.8 lbs/sec , a bit below design , but not much .............really not enough to cause the large amounts of surge slot discharge .
I may need to increase the IGV angle a tad more to create more preswirl , but my green manometer at 1260 mm water head vacuum indicates pretty high air velocities and static pressure drop already.
This compressor wheel is giving me a headache :-(
More thinking required .
I'll pull the engine apart and open up the NGV a tad to hopefully ease the compressor wheel out of surge , normally I'd just tighten the jetnozzle a tad to increase backpressure and P4t to increase thrust from an increase in TOT, but I feel that'll only exacerbate the surge problem .
Cheers John
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monty
Senior Member
Currently being spanked by mother nature.......
Joined: September 2018
Posts: 400
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Post by monty on Dec 13, 2023 9:40:42 GMT -5
John,
Haven't gotten a chance to re-write my spreadsheet yet. I have re-derived the work relationships. I have a hunch the problem is specific speed mismatch between the comp wheel and turbine. When I solved things for the choked exducer condition, I had a chance to play around with the behavior of the system a bit. It seemed the larger diameter wheels are building pressure too fast. Before the turbine is able to efficiently "digest" the flow. I haven't been able to play with the choked NGV condition yet. There is an ideal ratio of the turbine inducer tip speed to the Euler work vector. If things stray too far from that point the efficiency suffers quite a bit. A large vortex forms in the inducer passage. This happens either side of the ideal case. So it's possible to have the correct area and the wrong NGV angle, shallow or tight. I hope I can get to this problem this week. Rough week at work though, it might be next week before I can really look at it.
Monty
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Chuks
Senior Member
Joined: August 2015
Posts: 498
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Post by Chuks on Dec 13, 2023 14:39:45 GMT -5
Hi John. feels good to see its running again.
you said, "The trailing last half of the vanes isn't welded so able to be bent a bit to open up the throats , previously I was running 11mm throats now its only 9.2mm , so maybe a 10mm throat would be a good compromise" can you share pictures of how you are able to achieve that? thanks.
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Post by racket on Dec 13, 2023 15:25:03 GMT -5
Hi Chuks
I'll take some pics when I do the adjustment :-)
Cheers John
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Post by racket on Dec 13, 2023 16:10:33 GMT -5
Hi Monty
Yep , we're forced to work with turbocharger parts that have different requirements , turbochargers have an excess of energy entering the turb stage , so need real need to be too concerned about efficiency but are concerned about keeping the rate of acceleration as low as possible along with costs , we just have to wear the consequences :-(
If we can get an 80% efficiency it'll do the job :-)
Cheers John
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