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Post by madpatty on Jan 2, 2021 9:14:39 GMT -5
All, That is an interesting paper, as are all the others that are offered free on the Dyrobes site...highly recommended by us all I am sure. Just to clarify though, the paper is discussing the behavior of floating journal bearings, not squeeze film dampers. Additionally, in particular to the SFD design, I recommend that you wander over to Texas A&M University's Rotordynamics Laboratory, specifically, to Dr. Luis San Andrés's "Modern Lubrication Theory series, Lecture 13. Here is a perma-link: oaktrust.library.tamu.edu/handle/1969.1/93197Or here is the site location: rotorlab.tamu.edu/TRIBGROUP/default.htmthen navigate down to Lecture 13. It is much more informative for someone learning rotordynamics than the little bits that can get gleaned from the bits and pieces that you typically find in the technical papers. I also highly recommend poking around the TAMU Rotor Lab Tribology Group's site for all kinds of other rotordynamics gold. Patty, what kind of damping value are you trying to achieve? Are you doing any simulations to try to get it to a good spot, or are you just trying to experiment with it? Enjoy, Chris Hi Chris. Honestly I am chasing any damping I can get. But my models have taken into account a value of approx. 8 N-s/mm. Regards
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Post by racket on Jan 2, 2021 17:41:38 GMT -5
Hi Patty
You may need to make the damper holding bolt hole a blind hole and/or increase your lube pressure .
What results did you achieve when testing the lube flow to the damper using oil rather than diesel ??
What pressure did you use ??
How much oil exited the various holes ??
The "hairs on my butt" are telling me you might not be able to get things right without a remake of your shaft tunnel so that things can be accomodated/positioned/constructed better , sometimes a "modification" can't be done to achieve that end , its only a half way result due to limitation of the original design.
Cheers John
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Post by madpatty on Jan 2, 2021 20:23:29 GMT -5
Hi Patty You may need to make the damper holding bolt hole a blind hole and/or increase your lube pressure . What results did you achieve when testing the lube flow to the damper using oil rather than diesel ?? What pressure did you use ?? How much oil exited the various holes ?? The "hairs on my butt" are telling me you might not be able to get things right without a remake of your shaft tunnel so that things can be accomodated/positioned/constructed better , sometimes a "modification" can't be done to achieve that end , its only a half way result due to limitation of the original design. Cheers John Hi Racket. The bolt hole was leaking the maximum oil during pressure testing. I would say at 1 bar supply pressure total flow was close to 400-500 ml/min ~80% through the bolt hole, ~5% through the 2 lube holes and rest through the front (compressor side) leaking O-ring. The way this shaft tunnel is designed, its very similar to RC type shaft tunnels with thinner cross sections and "I" type structure so no meat at the centre of it. I only have 2.5mm wall thickness left at the centre region so can't make any drain channels. Me also thinks Redesign needed. Regards.
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Post by madpatty on Jan 3, 2021 21:30:57 GMT -5
Hi Guys.
I was playing around with the rotor dynamics, trying to find a suitable configuration of this rotor bearing system, where the forces transmitted to the bearings are lesser.
I tried several design iterations which we normally carry out with our jet engines like making shaft thicker by putting a sleeve spacer between bearings, lengthening the shaft by adding a shaft extension, changing the location of the bearings on the shaft, to name a few.
Most configurations caused bearing forces to shoot up like anything except two- Adding a spacer between bearings and moving the rear(turbine) bearing near the turbine.
Now spacer addition causes the bending critical to increase. In our rotors(TV94, HX82) it generally occurs near ~80k rpm so we are already almost safe but adding a spacer increased it beyond 100k rpm, even better. Also adding the spacer slightly decreased the forces transmitted to the bearings at conical modes(occurring at 20-25k rpm).
The biggest effect as many would’ve already guessed is moving the turbine side bearing closer to the turbine (reducing the turbine overhang). In my design iteration I have the capability to add bearing to any point on the entire rotor, so to experiment I moved the bearing to the point where the turbine side piston seal goes.
Force to turbine bearing decreased from 9.5kN to just 1.8kN
The unbalance in the rotor was kept same at 130g.mm for this simulation.
Cheers.
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Post by racket on Jan 3, 2021 22:13:38 GMT -5
Hi Patty
Probably why the GTBA engine has tried machining "back" the turb boss to move the bearing closer to the wheel , but with the exact weld position unknown it can be risky .
Cheers John
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Post by madpatty on Jan 4, 2021 2:36:55 GMT -5
Hi racket . DO you seem to have some pictures of your FM-1 and 9/94 shaft tunnel and maybe some ideas on how to route the lube oil channels I have having hard time trying to figure out how to route in/out the oil channels. Also how do you design O-rings grooves. How much squeeze and all? Regards.
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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: 230
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Post by ripp on Jan 4, 2021 2:45:24 GMT -5
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Post by racket on Jan 4, 2021 2:48:19 GMT -5
Hi Patty
It was a long time ago , most pics would have been on the old Yahoo Site , I didn't keep much info on the 9/94 as it was a pretty fast build and the 10/98 was in the pipeline before I'd really finished it .
I'll have a look through the CDs I have to find whats here .
The O'ring grooves ............if I remember correctly I had problems getting just the right depth so that there was a firm push required on the cup to fit it into its recess, but not too firm that it overode the preload .
Do you intend using a "cartridge" or individual cups ??
Cheers John
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Post by madpatty on Jan 4, 2021 2:52:44 GMT -5
Hi Patty It was a long time ago , most pics would have been on the old Yahoo Site , I didn't keep much info on the 9/94 as it was a pretty fast build and the 10/98 was in the pipeline before I'd really finished it . I'll have a look through the CDs I have to find whats here . The O'ring grooves ............if I remember correctly I had problems getting just the right depth so that there was a firm push required on the cup to fit it into its recess, but not too firm that it overode the preload . Do you intend using a "cartridge" or individual cups ?? Cheers John Hi Racket. Cartridge will give more damping so I am leaning towards that. Maybe I can get away with O-rings this way as I will already have a pretty long damper and not have to worry about O-rings on hotter side as well. O-rings like you said is critical in our case. Old yahoo site is gone with all the data as well. Regards.
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Post by racket on Jan 4, 2021 22:02:31 GMT -5
Hi Patty
Well , I've looked and I've looked , but can't find any pics :-(
Lotsa pics from 2008 and 2010 but it seems 2009 was either lost or I didn't take many , too long ago and too many builds inbetween .
OK , if you want to go cartridge then you'll need to have a blind hole at the securing bolt to prevent leakage if you want to continue using bleed fuel lubrication to the bearings .
It would be possible to use fuel as the squeeze film fluid to save having a seperate system , I'd invisage 2 small bore lines feeding the "fluid" into the bottom of the damper , one line at each end under the bearing position , the fluid should push any air out of the system as it works its way up to the top and out through either the securing bolt or a pair of return lines positioned above the delivery ones .
Ideally you probably want at least 3 Bar of delivery pressure to make sure the fluid is flowing freely across the damper
Cheers John
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Post by madpatty on Jan 5, 2021 2:38:47 GMT -5
Hi Racket. No problems. I'll figure out something. I am pretty skeptical at using fuel for damping due to it's very low viscosity but it's worth trying. Also what were your bearing positions on the turbine shaft? Same as where brass bush journals are? The 74mm OD of the shaft tunnel for your 9/94 engine is quite tight keeping in mind that you used 47mm OD bearings that too mounted in bronze cups. How did you channelize the oil inlet and outlet? The bearings you used are quite bigger than mine. I think mine are just marginal for the loads posed by this big rotor. Regards.
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Post by racket on Jan 5, 2021 3:16:47 GMT -5
Hi Patty Yep , my ball bearings were placed in the same position as the brass bushes. The fact that they were much larger than your current bearings undoubtedly allowed me to get through those early ( lowish RPM) whirl modes unscathed until I ran into the vibes ~50,000 rpm . Once I'd started getting the dampers doing their job I was able to use the smaller Allison C20 bearings 20 X 42 X 12 , probably helped also by the pressure balancing labyrinth seal behind the comp wheel that reduced shaft axial thrust. If you are using diesel for fuel then it might be OK for the damper , but yes I agree some normal light grade oil would be better . Maybe have another look at this Paper I posted last year www.academia.edu/21192172/Elastomer_O_Rings_as_Centering_Spring_in_Squeeze_Film_Dampers_Application_to_Turbochargers . The bronze cup probably only had a wall thickness of ~4 mm If you checkout imgbb.com/Qdx8gMJ the lube was fed into a gallery that had an angled drill hole feeding the lube to a circumfrential groove around the bronze cup , there was a blind radial hole drilled from the groove that the lube jet drill hole intersected , the jet was aimed at the inner raceway which requires the lube to be forced onto it otherwise it "runs dry" , the outer raceway has centrifuged lube and is easily take care of. My 6204 bearings probably had at least twice the load carrying capacity of yours , and even when I ran standard C3 bearings I was able to idle at 30,000 rpm without problems . Cheers John
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Post by madpatty on Jan 5, 2021 3:51:24 GMT -5
Hi Racket.
Damper length changes by 1/(viscosity)^1/3.
For diesel fuel which is approx. 10 times less viscous than 15W-40 at room temperature, I will need almost 2.15 times damper length to get same damping. Quickly running the Cals for my setup, I will need a damper close to 40mm in length if using diesel, sorta risky.
On a side note, I read that paper multiple times, the viscosity used in that paper for SFD lube is same as 15W-40 at 60 degrees Celsius.
Regards.
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Post by turboron on Jan 5, 2021 7:26:15 GMT -5
Patty, I support using the 15W-40 or other oil to the damper. My concern is that the longer damper sleeve will cause problems.
Thanks, Ron
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Post by racket on Jan 5, 2021 15:22:19 GMT -5
Hi Patty
Have you considered simply fitting a couple of bigger bearings ??
Cheers John
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