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Post by racket on Jun 17, 2023 18:59:31 GMT -5
Hi Andy
Nope , only 127 mm inducer but 7075 material so 70 psi would be no problem , don't know about the turb wheel though :-(
Cheers John
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Post by finiteparts on Jun 18, 2023 21:54:32 GMT -5
Hi John,
I was watching your runs and thought I would have a go at calculating the rotor speed from the acoustic blade passing frequencies with the spectrum analyzer and some calcs.
On your March 22nd test run, with AB duct, but dry, I am getting 61,885 rpm when your P2 gage shows ~ 3.5. Now on your most recent test, with the AB duct,dry, I am getting 60,188 rpms.
It is likely that the reduced NGV area reduced the mass flow, thus shifting the compressor op-line over to the left. This would be consistent with the same P2 but reduced rpm, but the IGV and diffuser mods might also be at play. This new compressor appears to be running consistently lower in speed to produce the same PR, since it was installed.
I am calculating roughly 3.35 lbm/s to get the 268 lbf at max AB, PR~ 4.5. Is that roughly the number you are getting?
I went back and checked some of your older runs, and this is what I collected...
6/9/2022 test: P2 gage ~ 3.0, 64,688 rpm (old compressor impeller)
12/16/2022 test: P2 gage ~ 3.0, 58,662 rpm (new compressor impeller)
12/20/2022 test: P2 gage ~ 3.0, 58,371 rpm ~ 3.5, 61,714 rpm
2/14/2023 test: P2 gage ~ 3.0, 58,328 rpm ~ 3.5, 61,088 rpm
3/4/2023 test: P2 gage ~ 2.0, 51,171 rpm ~ 3.0, 58,885 ~ 3.5, 62,382
3/22/2023 test: No AB (damaged turbine during test) P2 gage ~ 3.0, 58,431 ~ 3.5, 61,885 With AB
P2 gage ~ 3.0, 57,711 ~ 3.5, 60,205
6/16/2023 test: Max AB, 60,565 rpm (new turbine) Idle, 30,960 rpm No AB: P2 gage ~ 2.0, 49,714 rpm ~ 3.2, 58,714 rpm ~ 3.5, 60,188 rpm
Just thought I would share and hoping that it helps something "click" in your mind about what may be going on.
Good luck,
Chris
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Post by finiteparts on Jun 19, 2023 13:30:07 GMT -5
John, I was thinking about what instrumentation that you had available on your tests and if there was sufficient information to back-calculate the mass flow and I think there is enough to get some pretty good ballpark numbers. Because you have a total pressure measurement in the exhaust stream, and when you are not running a nozzle or AB setup, we can assume from the free jet theory that the static pressure at total pressure probe location is equal to the ambient pressure. With a local total and static pressure value, we can use the compressible flow function to find the mass flow with a few assumptions. The compressible flow function can be found in many resources, but I pulled this formulation from J.H. Horlock's "Axial Flow Turbines, Fluid Mechanics and Thermodynamics". It is very useful because it allows the correlation of pressure ratio data and other flow variables that are relatively measurable. The trick here is to realize that you have roughly all the information needed to calculate the right hand side (RHS) of the equation. Then you can reformulate the LHS to solve for the mass flow and calculate it from the other known/assumed flow data, as shown below: Now, I don't have your fuel flow properties and so the gamma and specific gas constant are assumed to be 1.33 and 53.35 lbf ft / lbm R, respectively. As for the area, I took your 127 mm exducer diameter and initially used a discharge coefficient (Cd) of 0.9. This may be subject to variation, but the fact is that you will not have a uniform total pressure across the plane of measurement and we need to account for that somehow. It required iteration to get the flow function calculated mass flow to match the thrust that you mentioned (187 lbf) with the discharge Cd being varied. I ended up with a Cd ~ 0.74, which seems low based on theory, but like I said before, in reality the total pressure profile will vary across the plane and also the TC and Pt probes will produce losses. This is not perfect, but I would think this gets you within the ball park flow rate. So here are the numbers that I got using the data that I could see on the March 4th test: At the PR ~ 4.0 condition, I was getting 4.02 lbm/s At the PR ~ 4.5 condition, I was getting 4.79 lbm/s If you install a static pressure port on your exhaust section, or better yet, three or four that are averaging over the circumference, you could do this calculation for the test cases when you have the AB duct on the engine. Good luck, Chris
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Post by racket on Jun 19, 2023 19:55:45 GMT -5
Hi Chris You've raised some relevant issues and I went looking for something that might help explain the inconsistancies I experienced many years ago with the TV84 engine when trying to reconcile my total and static pressure readings in the jetpipe , and I've found this Paper www.jafmonline.net/article_2213_53a20ee0d016f3e47fb9977f3cc887b3.pdf . It seems the wake from the hub extends a considerable distance downstream and would account for why my jet nozzles were always larger than theoretical . I probably need to fit a 4 foot length of exhaust pipe with my readings being taken near the outlet I'm looking at doing a "dry" test on Thursday , weather permitting , 117 mm jet nozzle , with the load cell fitted instead of my 200 lb butchers spring balance , I did check each against themselves by hooking them in tandem and with me hanging off the end , the readings were within a pound or two , so close enough :-) Cheers John
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Post by racket on Jun 20, 2023 22:52:26 GMT -5
Hi Guys Todays test , rather disappointing thrust result considering it was fitted with a 117mm jet nozzle and only an extra 10 lbs of thrust compared to the previous test without any jet nozzle , I just don't understand whats going on youtu.be/X3cwhXU0F3Yyoutu.be/ITzogKz3flwyoutu.be/1GEL8d79_vQCheers John
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ripp
Veteran Member
I'm sorry, I don't speak english, so I torment you (and myself) with a translation program,Sorry
Joined: January 2013
Posts: 236
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Post by ripp on Jun 21, 2023 0:51:40 GMT -5
Hi John
how do you feel about the surg slot.
in the range 0.6 - 3.5 par , does a lot of air escape?
do you lose mass flow overall?
thanks Ralph
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ripp
Veteran Member
I'm sorry, I don't speak english, so I torment you (and myself) with a translation program,Sorry
Joined: January 2013
Posts: 236
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Post by ripp on Jun 21, 2023 1:25:58 GMT -5
interesting to see 0,9par 3,0par maybe a nice bell entrance would be beneficial, no harsh edge Cheers Ralph
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Post by racket on Jun 21, 2023 2:33:12 GMT -5
Hi Ralph
At the lower power setting theres considerable air exiting the surge slot , the red manometer measures the pressure in millimeters of water , at high power settings things become close to neutral , hence the string gets sucked towards the bellmouth inlet by the general airflow around the engine .
The surge slot certainly helps at lower power settings to dump enough flow to keep the comp from sort of "surging", rough airflow :-(
I've yet to view the Youtube vids at half speed to record the various parameters so that I can compare them with the test run on 9 June where I had an open jetpipe .
There were pluses with the test ,...... the spoolup was good , my P2 and P4t gauges were reasonably stable and my two TOT readings were fairly consistent , but that measly 10 lbs-4 kgs of extra thrust from fitting the jetnozzle , just doesn't seem right considering I was burning more fuel, the fuel pump was at max as the dump to tank was closed .
There wasn't much "colour" at the turbine at full power , just a dull red glow from the NGV area.
I'll get into the numbers tomorrow and see if I can find any sort of aberration :-)
Will keep you posted on what I find
Cheers John
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Post by stoffe64 on Jun 21, 2023 3:53:06 GMT -5
Maybe the starter setup is in the way? It become a disturbance when everything is fitted to the engine ? Scratching my head here! Interesting and frustrating at the same time!
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Post by racket on Jun 21, 2023 4:23:20 GMT -5
Hi Stephan
But I had the same bits in place on the previous test .
A couple of early observations , thrust at 1 Bar increased by 50% , at 2 Bar 25% , at 3 Bar 13% and 3.5 Bar ~5% ...................theres a trend going on here :-)
Temps were ~50 C degrees hotter across the entire power range .
Cheers John
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Post by stoffe64 on Jun 21, 2023 12:20:52 GMT -5
Hmmm,THAT was interesting, more speed less thrust gain,wonder why....Hmmm? Maybe need longer jetpipe? So the gasses can level out but temps would go up
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Post by stoffe64 on Jun 21, 2023 12:24:14 GMT -5
Me Again,i Think it need more air in to engine, if you go higher pressure you would loose thrust instead...Hmmm?
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Post by stoffe64 on Jun 21, 2023 12:28:11 GMT -5
It feel like the engine becomes shorter the higher pressure become
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Post by racket on Jun 23, 2023 20:04:11 GMT -5
Hi Guys A couple of mods before the next test run . New manometer mounting for easier viewing And a short extension on a rather badly abused jet nozzle to reduce the diameter by ~6 mm to ~111-112 mm I'll be ready for a testrun once the fuel tank is replenished Cheers John
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Post by finiteparts on Jun 24, 2023 12:37:54 GMT -5
Hi John,
I was thinking that maybe instead of looking at rpm, which can float due to ambient conditions, it would be better to report corrected speed, thus I would ask a quick favor to include the ambient temperature and humidity if it is not too much of an ask.
Also, can you include a picture of your total pressure probe and your EGT probe?
From the Pt/Ps ratio, it looks like your 117 mm nozzle throat Mach number is ~0.93, so I am wondering if you are starting to push up against the flow limits of the nozzle given the pressure ratio capability of the compressor system. The next test will be telling.
Good luck,
Chris
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