Qantas A380 uncontained #2 engine failure
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Bear - Once again I find myself astonished at the breadth and depth of your engineering knowledge.
I must confess that I had understood that material science had moved on rather since the J58's time, and that the disc temperatures on the HP and IP turbines of the Trent (and any other modern engines ) would be significantly higher than the J58's HP disc.
Certainly, my ignorance is such that I had thought the turbine entry temperature of the Trent was significantly higher than the J58 despite the absence of donuts and flame at the exhaust.
As to the materials involved, I'm afraid that I understood that the IP compressor discs (which you remember include rim, diapragmy middle bit and hub) are probably titanium, the connecting shaft will be a fancy steel, and the turbine dic will be a nickel alloy.
THE IP TURBINE DISC IS NOT TITANIUM. But, as ever, I stand to be corrected.
Sorry to raise my voice.
I must confess that I had understood that material science had moved on rather since the J58's time, and that the disc temperatures on the HP and IP turbines of the Trent (and any other modern engines ) would be significantly higher than the J58's HP disc.
Certainly, my ignorance is such that I had thought the turbine entry temperature of the Trent was significantly higher than the J58 despite the absence of donuts and flame at the exhaust.
As to the materials involved, I'm afraid that I understood that the IP compressor discs (which you remember include rim, diapragmy middle bit and hub) are probably titanium, the connecting shaft will be a fancy steel, and the turbine dic will be a nickel alloy.
THE IP TURBINE DISC IS NOT TITANIUM. But, as ever, I stand to be corrected.
Sorry to raise my voice.
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CAAAD
Hello again. The Turbojet is primarily locked into the creation of as much heat as possible, the Turbo Fan has the opposite mission, to squeeze out thrust that depends on the "efficient" and economical use of as little fuel as possible, whilst extending maintenance intervals to the maximum. The RR engine is so well developed that initially it was intended to have no "variable" Pitch Blades, it has one set, to mitigate surge.
"Archaic"?? All in the mind, Sir. Inconel has an extensive pedigree, as does the Propellor. The TRENT, actually all TurboFan engines utilize what amounts to a Propellor to translate heat into motion. The exhaust is warm, but instead of relying on it to move things along, it 'exhausts itself' into producing power to spin the "Propellor" in the front.
The TRENT relies on COOL temperatures to protect its guts. Heat is money, if not at the bowser, certainly at the OH side. Metal is speced to do what it does within limits of temperature, mechanicals, and cost. Regardless the composition of the Wheel(s), it is in this area that all of us can be confident in the extreme, relative to design, performance, and conversation.
I hope this is modern enough a reply.
bear
Hello again. The Turbojet is primarily locked into the creation of as much heat as possible, the Turbo Fan has the opposite mission, to squeeze out thrust that depends on the "efficient" and economical use of as little fuel as possible, whilst extending maintenance intervals to the maximum. The RR engine is so well developed that initially it was intended to have no "variable" Pitch Blades, it has one set, to mitigate surge.
"Archaic"?? All in the mind, Sir. Inconel has an extensive pedigree, as does the Propellor. The TRENT, actually all TurboFan engines utilize what amounts to a Propellor to translate heat into motion. The exhaust is warm, but instead of relying on it to move things along, it 'exhausts itself' into producing power to spin the "Propellor" in the front.
The TRENT relies on COOL temperatures to protect its guts. Heat is money, if not at the bowser, certainly at the OH side. Metal is speced to do what it does within limits of temperature, mechanicals, and cost. Regardless the composition of the Wheel(s), it is in this area that all of us can be confident in the extreme, relative to design, performance, and conversation.
I hope this is modern enough a reply.
bear
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Bear - No no no. You have lurched off on another tangent.
My point was that the king of efficiency is the turbine inlet temperature, and a large portion of engineering effort has gone into designing turbines and materials able to cope with astonishing temperatures. So the J58 turbine inlet temperature was very modest compared with all modern engines. As was the Avon etc.
We start with a very high gas temperature at turbine inlet and then we squeeze out as much energy as possible through the many lower stages of turbine such that the exhaust gas can scarcely trickle out of the jetpipe.
I'm afraid your analysis lacked a bit of precision since variable stators are to do with compressor surge margin and efficiency, not really a turbine temperature issue.
Anyway, many thanks for the explanation as to the purpose of the fan, I am sure many of us would have been unaware of that.
But do you agree that the IP turbine disc is not titanium?
My point was that the king of efficiency is the turbine inlet temperature, and a large portion of engineering effort has gone into designing turbines and materials able to cope with astonishing temperatures. So the J58 turbine inlet temperature was very modest compared with all modern engines. As was the Avon etc.
We start with a very high gas temperature at turbine inlet and then we squeeze out as much energy as possible through the many lower stages of turbine such that the exhaust gas can scarcely trickle out of the jetpipe.
I'm afraid your analysis lacked a bit of precision since variable stators are to do with compressor surge margin and efficiency, not really a turbine temperature issue.
Anyway, many thanks for the explanation as to the purpose of the fan, I am sure many of us would have been unaware of that.
But do you agree that the IP turbine disc is not titanium?
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"We start with a very high gas temperature at turbine inlet and then we squeeze out as much energy as possible through the many lower stages of turbine such that the exhaust gas can scarcely trickle out of the jetpipe."
That's interesting, never thought of it that way. So ideally the fan produces 100 percent of the thrust, right? We're actually all traveling around at mach .87 behind ducted propellers, essentially...no more of the old action/reaction jet-thrust exhaust.
That's interesting, never thought of it that way. So ideally the fan produces 100 percent of the thrust, right? We're actually all traveling around at mach .87 behind ducted propellers, essentially...no more of the old action/reaction jet-thrust exhaust.
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To the crowd who have never really studied the physics of a gas turbine:
You would be amazed at the temperature rise through the compressor - many thousands of internal shaft horsepower bucking up P and T across a dozen-to-twenty stages.
You would also be amazed at the P and T extracted by each turbine stage in driving each compressor or fan.
I'm speaking here of any high-bypass turbofan - PW4000, Trent, CF6, two-spool, three-spool...
That said, a pure turbojet (J58, J75, Olympus etc) runs relatively cool through its turbomachinery cycle. Only about 25% of the available oxygen is burned. The other 75% is available for the afterburner (OK,OK, augmenter or relight) to use. THAT'S where the real hot-hot temperature and velocity (exhaust diamonds and REALLY LOUD NOISE) come from. But that's ALL DOWNSTREAM of the turbine.
You would be amazed at the temperature rise through the compressor - many thousands of internal shaft horsepower bucking up P and T across a dozen-to-twenty stages.
You would also be amazed at the P and T extracted by each turbine stage in driving each compressor or fan.
I'm speaking here of any high-bypass turbofan - PW4000, Trent, CF6, two-spool, three-spool...
That said, a pure turbojet (J58, J75, Olympus etc) runs relatively cool through its turbomachinery cycle. Only about 25% of the available oxygen is burned. The other 75% is available for the afterburner (OK,OK, augmenter or relight) to use. THAT'S where the real hot-hot temperature and velocity (exhaust diamonds and REALLY LOUD NOISE) come from. But that's ALL DOWNSTREAM of the turbine.
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stepwilk:
Oh, action-reaction still applies, just as it always did ever since the Wright Bros. It's merely a matter of degree. In fact, the fan produces 75-80% of thrust, and the core exhaust the remainder.
But when I was instructing on an early turbofan (OMG - 40 years ago!) I had to get the whole fan thrust concept across to technicians in their language. I called it a "Fixed-pitch, direct-drive, multiblade ducted propeller" - and after they thought about that a minute or so, they understood the concept.
That's interesting, never thought of it that way. So ideally the fan produces 100 percent of the thrust, right? We're actually all traveling around at mach .87 behind ducted propellers, essentially...no more of the old action/reaction jet-thrust exhaust.
But when I was instructing on an early turbofan (OMG - 40 years ago!) I had to get the whole fan thrust concept across to technicians in their language. I called it a "Fixed-pitch, direct-drive, multiblade ducted propeller" - and after they thought about that a minute or so, they understood the concept.
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@ post 1362 I don't know anything about Trent engines, but judging by the size of the fan (It seems to be twice the height of a man by looking at some photos) I don't see how it can be direct drive.
If the LP turbines are running at 3,000 rpm (as mentioned earlier in the thread) there must be reduction gears for the fan (Unless the fan blade tips are well supersonic)
Flight Idle.
If the LP turbines are running at 3,000 rpm (as mentioned earlier in the thread) there must be reduction gears for the fan (Unless the fan blade tips are well supersonic)
Flight Idle.
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Originally Posted by stepwilk
So ideally the fan produces 100 percent of the thrust, right?
regards,
HN39
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Flight Idle
The 116 inch single stage fan is driven directly by 5 turbines. The only large geared turbofan engine in development at the moment is a PW design.
Thanks to Mr. Zimmer the Quick's link:
Thanks to Mr. Zimmer the Quick's link:
The 116 inch fan operates at nearly 3,000rpm with tip speeds 1.5 times the speed of sound
Last edited by vapilot2004; 25th Nov 2010 at 21:13. Reason: copy & paste fail per Mr. Zimmerfly. cheers!
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I think you will find the fan is driven by a 5 stage turbine
The HPC is connected to the HPT
The IPC is connected to the IPT
The Fan is connected to the LPT.....(could almost set that to music)
Stages:
- Fan
- 8-stage intermediate pressure compressor (IPC)
- 6-stage high pressure compressor (HPC)
- Annular combustor
- Single-stage high pressure turbine (HPT)
- Single-stage intermediate pressure turbine (IPT)
- 5-stage low pressure turbine (LPT)
- Fan
- 8-stage intermediate pressure compressor (IPC)
- 6-stage high pressure compressor (HPC)
- Annular combustor
- Single-stage high pressure turbine (HPT)
- Single-stage intermediate pressure turbine (IPT)
- 5-stage low pressure turbine (LPT)
The IPC is connected to the IPT
The Fan is connected to the LPT.....(could almost set that to music
)
Last edited by ZimmerFly; 25th Nov 2010 at 20:30. Reason: clarity
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@ post 1362 I don't know anything about Trent engines, but judging by the size of the fan (It seems to be twice the height of a man by looking at some photos) I don't see how it can be direct drive.
If the LP turbines are running at 3,000 rpm (as mentioned earlier in the thread) there must be reduction gears for the fan (Unless the fan blade tips are well supersonic)
If the LP turbines are running at 3,000 rpm (as mentioned earlier in the thread) there must be reduction gears for the fan (Unless the fan blade tips are well supersonic)
It is not geared, and the fan blade tips are indeed "well supersonic".
Geared turbo fans do exist, allowing more flexibility to optimise LP turbine and fan speeds, but I am not aware of RR making anything of that type.
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You sure?
Not 'challenging' you at all, just wondering how that fits in with maximum efficiency in cruise.
And yes, I know the the Harvard (T-6, Texan) prop tips were supersonic most of the time (made them most distinguishable, noise-wise...) but I can't see how that would work on a large fan.
CJ
Not 'challenging' you at all, just wondering how that fits in with maximum efficiency in cruise.
And yes, I know the the Harvard (T-6, Texan) prop tips were supersonic most of the time (made them most distinguishable, noise-wise...) but I can't see how that would work on a large fan.
CJ
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Zimmerfly, do you fancy nipping a few miles down Derby Road with a couple of bits of the turbine? I know you have very good facilities up there, but we probably have better 
!
!
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Bear - Please return to the point under discussion, which was whether the Trent has a higher turbine entry temperature than the J58. Of course it does.
And that temperature is a carefully developed trade off between efficiency and durability.
Once again your knowledge in this field outstrips mine because I don't know what 'core temperature' is.
Have you finally come to the view that the IP Turbine Disc is not titanium? Is this closure? Can the metallurgical enthusiasts relax?
And that temperature is a carefully developed trade off between efficiency and durability.
Once again your knowledge in this field outstrips mine because I don't know what 'core temperature' is.
Have you finally come to the view that the IP Turbine Disc is not titanium? Is this closure? Can the metallurgical enthusiasts relax?
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You sure?
Not challenging either, but the fact that the peripheral velocity is higher than the speed of sound (in your example at sea level, normal atm. conditions), does not necessarily mean the tips of the fan blade are running supersonic. I assume that their swept back design (looking from the front), prevents that, much like the sweep on the wings of airplanes is designed / implemented for that reason. It could be hard to imagine how complicated an airflow over a blade would be, if part of it is subsonic (root), transonic and supersonic (as we approach the tip) and how this varies at different RPMs. Besides the implications of mach waves across the tips and in such tight tolerances with the nacelles, would induce high energy losses, impact on efficiency and structural complications to take into consideration tip foil design, blade structural design to take into consideration varying loads in transonic phase, internal nacelle design ( to take into consideration 2 flow types, sub/ supersonic) and of course noise abatement which is a considerate factor for the airframe manufacturer.
Again, not an expert on modern aircraft engines but I assume the flow is subsonic or well near transonic.. I f anything can confirm this or the opposite, thnx in advance....
Again, not an expert on modern aircraft engines but I assume the flow is subsonic or well near transonic.. I f anything can confirm this or the opposite, thnx in advance....