Compressor stall? How do U explain this?
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Compressor stall? How do U explain this?
Hello gents...
Did anyone check this out already?
http://www.airliners.net/open.file?i...&sok=&photo_nr=
The pix tag says compressor stall. Is this the case of a catastrophic failure or the jet-version of a detonation in a piston engine? I would like to discuss this topic after few opinions where given...damn good stuff for powerplant ground lessons, I guess.
Kind regards
PZ
Did anyone check this out already?
http://www.airliners.net/open.file?i...&sok=&photo_nr=
The pix tag says compressor stall. Is this the case of a catastrophic failure or the jet-version of a detonation in a piston engine? I would like to discuss this topic after few opinions where given...damn good stuff for powerplant ground lessons, I guess.
Kind regards
PZ
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Definitely looks like a cpr stall - in reverse thrust.
Essentially it's the result of loss of pumping capacity by one or more stages in the compressor, resulting in the remaining stages being overloaded and losing their ability to contain the high-pressure air in the combustor section. The fuel-air mix "burbs" out the front, then reingests and blows out the back. Generally sounds like a cannon shot!
It may be a very transient phenomenon, a temporary mismatch between stages. During engine accel it's likely to be the front stages trying to pump more than the aft stages can deliver to the burner. Engine developers work hard to prevent this, but r/t and especially crosswinds can defeat their efforts.
Essentially it's the result of loss of pumping capacity by one or more stages in the compressor, resulting in the remaining stages being overloaded and losing their ability to contain the high-pressure air in the combustor section. The fuel-air mix "burbs" out the front, then reingests and blows out the back. Generally sounds like a cannon shot!
It may be a very transient phenomenon, a temporary mismatch between stages. During engine accel it's likely to be the front stages trying to pump more than the aft stages can deliver to the burner. Engine developers work hard to prevent this, but r/t and especially crosswinds can defeat their efforts.
PZ I'm not sure how deep you want to go in this and for what purpose.
For starters do a search in this forum on engine surge/stall. probably all that could be said you will find here, along with lots that should not have been said
I like barit1 KISS answer
If you need more than simply lead back with a simple question or two after you have done the search recommended above.
For starters do a search in this forum on engine surge/stall. probably all that could be said you will find here, along with lots that should not have been said
I like barit1 KISS answer
If you need more than simply lead back with a simple question or two after you have done the search recommended above.
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I'll stick with barit1 asw, just deepen my qs a bit...
To my knowledge (pilot), the "burp" of fuel-hp air mixture from the aft to the fwd and aft again sections of compressor is ejected through the combustion chambers and the exhaust not completely burnt and ignited outside. That should explain the spectacular firebreath of the pix, ain't? My qs was also about overall consequences on engine components after that. barit1 gave also another nice tip to ask for. Why r/trusth and x/wind are more suitable condition for this phenomenon? My engineering past is a long way behind me...I forgot most of the concepts...Uni wasn't exactly the way I wanted to go!
Thanks for the fun
PZ
To my knowledge (pilot), the "burp" of fuel-hp air mixture from the aft to the fwd and aft again sections of compressor is ejected through the combustion chambers and the exhaust not completely burnt and ignited outside. That should explain the spectacular firebreath of the pix, ain't? My qs was also about overall consequences on engine components after that. barit1 gave also another nice tip to ask for. Why r/trusth and x/wind are more suitable condition for this phenomenon? My engineering past is a long way behind me...I forgot most of the concepts...Uni wasn't exactly the way I wanted to go!
Thanks for the fun
PZ
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Distorted inlet airflow, or sometime reingestion or cross-ingestion is frequently the cause of a stall/surge. Crosswinds and/or r/t can produce the this
During this very transient event, the airflow through the burner is greatly reduced but the fuel flow is still about the same, so there's a temporary over-rich mixture that doesn't fully burn inside the intended space - thus the fireball. (There may be a series of them... organ-pipe effect you know)
If it doesn't last too long there may be no real damage, because the heat is so intermittent it doesn't raise the metal temperature much. But the mfr probably will require some kind of inspection to be sure.
During this very transient event, the airflow through the burner is greatly reduced but the fuel flow is still about the same, so there's a temporary over-rich mixture that doesn't fully burn inside the intended space - thus the fireball. (There may be a series of them... organ-pipe effect you know)
If it doesn't last too long there may be no real damage, because the heat is so intermittent it doesn't raise the metal temperature much. But the mfr probably will require some kind of inspection to be sure.
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PZ
BTW:thanks for joining this matter...
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The complex answer is that a jet engine is a Brayton cycle engine, thtat's what they told us in school, but I don't know what it means.
The last stage of compression, is the point of highest pressure in the engine. The burner can generally opens up in area. This would generally cause the pressure to drop but it only drops a little due to the addition of fuel and combustion. The rear end of the burner section opens even further giving more pressure drop but a large increase in velocity.
If inlet airflow is disrupted, which allows the last stage of compression pressure to drop, the burner pressure will be higher. The air finds it easier to go back out the front of the engine rather than through the turbine section. Another cause could be too high burner pressure, due to too much fuel,
same result, different cause.
The primary thing is that the air finds it easier to go out the front rather than through the engine. The picture shows a combination of increased pressure in the rear of the engine due to thrustreverser deployment and disrupted inlet airflow.
I hope you are now confused at a much higher level.
The last stage of compression, is the point of highest pressure in the engine. The burner can generally opens up in area. This would generally cause the pressure to drop but it only drops a little due to the addition of fuel and combustion. The rear end of the burner section opens even further giving more pressure drop but a large increase in velocity.
If inlet airflow is disrupted, which allows the last stage of compression pressure to drop, the burner pressure will be higher. The air finds it easier to go back out the front of the engine rather than through the turbine section. Another cause could be too high burner pressure, due to too much fuel,
same result, different cause.
The primary thing is that the air finds it easier to go out the front rather than through the engine. The picture shows a combination of increased pressure in the rear of the engine due to thrustreverser deployment and disrupted inlet airflow.
I hope you are now confused at a much higher level.
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Definitely looks like a cpr stall - in reverse thrust.
Essentially it's the result of loss of pumping capacity by one or more stages in the compressor, resulting in the remaining stages being overloaded and losing their ability to contain the high-pressure air in the combustor section. The fuel-air mix "burbs" out the front, then reingests and blows out the back. Generally sounds like a cannon shot!
Essentially it's the result of loss of pumping capacity by one or more stages in the compressor, resulting in the remaining stages being overloaded and losing their ability to contain the high-pressure air in the combustor section. The fuel-air mix "burbs" out the front, then reingests and blows out the back. Generally sounds like a cannon shot!
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This happened to an RNZAF 757-200 last year and the surge of pressure against fan blades from behind cracked many of the blades. The entire engine needed to be pulled.
Aircraft which keep flying after such an incident risk losing fan blades in flight during future flights.
Aircraft which keep flying after such an incident risk losing fan blades in flight during future flights.
This happened to an RNZAF 757-200 last year and the surge of pressure against fan blades from behind cracked many of the blades. The entire engine needed to be pulled.
Aircraft which keep flying after such an incident risk losing fan blades in flight during future flights.
Aircraft which keep flying after such an incident risk losing fan blades in flight during future flights.
Any details to clarify or support this?
More typically compressor blades and not fan blades were involved. Typically cracked compressor blades precede the surge, by one of the blades coming loose in the gas stream. On rare occasions repeated surging left unabated over a minute or so could crack the compressor blades.
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I spent 16 years flying aeroplanes that surged merrily- VC10 and B747-100 (Pratt & Whitneys) and to a lesser extent, B747-200s. Surging caused no ongoing problems. I believe they are no more serious than a backfiring car- indeed usually if the engine parameters recover themselves, you can leave the engine running normally. A surge with no reasonable cause, like power change, is often a 'don't use', 'no relight unless really needed' restriction. As long as they don't bang for too long they are harmless. The cause is incorrect pressure distribution through the engine, usually just pressure relief valves not spring loading open to relieve excess pressure, so the air finds a new way to go!
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Compressor stalls on the number 2 engine was and still is a problem in the Boeing 727 during takeoff with a strong crosswind from either side around 60 or more degrees with wind near 20 knots or higher.
Standard procedure to avoid this problem was bring 1 and 3 up to max EPR while sitting static on the end of the runway. As airspeed increased to 70-80 IAS either the NPF of the FE would bring #2 up to max EPR. The stronger the crosswind the more airspeed was needed to avoid the compressor stall. However, sometimes no matter what you did you would still have the #2 bang a couple of time.
As far as I know the 727 was the only tri-jet to have this problem. I know the Falcon 50/900 had no problems in this area.
Standard procedure to avoid this problem was bring 1 and 3 up to max EPR while sitting static on the end of the runway. As airspeed increased to 70-80 IAS either the NPF of the FE would bring #2 up to max EPR. The stronger the crosswind the more airspeed was needed to avoid the compressor stall. However, sometimes no matter what you did you would still have the #2 bang a couple of time.
As far as I know the 727 was the only tri-jet to have this problem. I know the Falcon 50/900 had no problems in this area.
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I don't recall where I read this but I have read an article that engine surges can send supersonic shock waves forwards through the fans and then in an instant the flow reverses again. The effect is like bending metal very quickly in two directions, just like the forces which snapped the tail of that AA A300 over New York in 2001. The result (so I read in the article) is to cause minute hairline cracks in the fan blades which will propagate.
Worth asking some engineer types to comment?
Worth asking some engineer types to comment?
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Let's not sensationalise them! They do send shocks through the engine- an engine designed to operate at temperatures down to -70 degrees C or colder...in severe turbulence....with ice forming on the fan blades causing vibration....to withstand the shock of landings (like mine)....with rapidly changing thrust and acceleration. If an engine cannot take the shock of a surge without damage, it should not be licensed for passenger use! I repeat what I have said before, surges are harmless. I have never known, even in a large airline like BA, a surge to result in damage. I have seen repeated surging at high reverse power for several minutes (to stop rolling), no damage done, aircraft flew quite happily next day. Early 747s were surge monsters....again harmless. They are just a backfire, and bland with it.
I take issue with the expression 'supersonic' shock waves, just shock waves will do, and I really see no connection between fan blades and Airbus fins which is a totally separate and unconnected issue! Engines can take it quite happily, just as they take the shock of startup and the explosion of fuel then every time they operate!
I take issue with the expression 'supersonic' shock waves, just shock waves will do, and I really see no connection between fan blades and Airbus fins which is a totally separate and unconnected issue! Engines can take it quite happily, just as they take the shock of startup and the explosion of fuel then every time they operate!
Last edited by Rainboe; 22nd Nov 2006 at 07:08.
