- #1
anvesh111
- 32
- 0
why the spools(twin spool,triple spool) are used in compressors,why the stages in compressor must be increased
Last edited by a moderator:
FredGarvin said:Your question doesn't make a whole lot of sense to me in the current form Can you restate it? It appears that you are asking why if you have multiple spool engines must the number of compressor stages increase. Is this correct?
I mean allowed in that compressors are constantly working against an adverse pressure gradient which places a lot of limitations on what kind of delta P across a stage you can have. Has anyone ever noticed that all jet engines (with axial compressors) have a much larger number of compressor stages than the turbine?mugaliens said:By "allowed," I take it to mean you're referring to what the laws of physics allow? Or is it simply a case design optimization, whereby obtaining the same, final compression ratio via multi-stage axial compression does not require planetary gearing or substantially greater weight or strength of materials than would a design with fewer stages?
FredGarvin said:I mean allowed in that compressors are constantly working against an adverse pressure gradient which places a lot of limitations on what kind of delta P across a stage you can have.
Has anyone ever noticed that all jet engines (with axial compressors) have a much larger number of compressor stages than the turbine?
Not in an axial machine. You can with a radial/centrif if you want.mugaliens said:You can design for a very high stage differential pressure, if you want. It's just terribly inefficient. :)
One word answer: separation.mugaliens said:Yes. Why is that, Fred?
FredGarvin said:Not in an axial machine. You can with a radial/centrif if you want.
One word answer: separation.
You're right. What do I know.mugaliens said:Separation occurs when turbines designed for a one pressure differential encounter a significantly greater pressure differential. It's a consequence of the design, as efficiency is highest when operated closest to the stall line.
Turbines with fewer stages and specifically designed for higher per stage pressure differentials do not experience separation within their design parameters. However, as I've mentioned, they're significantly less efficient than turbines designed for optimal efficiency, and which, as a consequence of their design, have more stages.
In short, it's entirely doable. It's simply not practical.
minger said:Whoa whoa, apparently your sarcasto-meter didn't pick me up properly.
We do centrifugal compressors, but I know enough about axial systems to know that a 20:1 pressure ratio (for example) on a 5' fan blade is going to cause some issues.
yeah..i agree with you...thanksmugaliens said:Absolutely. As I said, it's not impossible. Merely grossly inefficient, and therefore impractical.
A similar, and familiar approach would involve a ramjet. Below Mach 0.5, they have almost zero thrust due to poor compression ratios, and below 600 kts, they're grossly inefficient. Between Mach 2 and 4, however, they'll outperform any turbojet.
The issue is one of compression. In a turbojet, we obtain efficiency by using multiple compression stages. A ramjet achieves efficiency by means of high mach to achieve that compression.
In a one-stage design, achieving a 20:1 compression ratio is "easy": just increase the velocity. When we do so, however, we find that achieving that high of a compression ratio requires a mach turbine (airflow over the turbines is mach), which introduces all kinds of wonderful problems.
Grossly inefficient. Very impractical.
But possible.
Again, we do not use multiple stages because achieving high compression with one stage is impossible. We do so because using multiple stages is much more efficient.
It is grossly apparent that you have never even seen a compressor in real life. I would suggest you read Hill and Peterson. You have linked to it. Try reading it especially section on axial compressors.mugaliens said:Absolutely. As I said, it's not impossible. Merely grossly inefficient, and therefore impractical.
A similar, and familiar approach would involve a ramjet. Below Mach 0.5, they have almost zero thrust due to poor compression ratios, and below 600 kts, they're grossly inefficient. Between Mach 2 and 4, however, they'll outperform any turbojet.
The issue is one of compression. In a turbojet, we obtain efficiency by using multiple compression stages. A ramjet achieves efficiency by means of high mach to achieve that compression.
In a one-stage design, achieving a 20:1 compression ratio is "easy": just increase the velocity. When we do so, however, we find that achieving that high of a compression ratio requires a mach turbine (airflow over the turbines is mach), which introduces all kinds of wonderful problems.
Grossly inefficient. Very impractical.
But possible.
Again, we do not use multiple stages because achieving high compression with one stage is impossible. We do so because using multiple stages is much more efficient.
FredGarvin said:It is grossly apparent that you have never even seen a compressor in real life.
mugaliens said:Gee, Fred, I must have missed 'em sitting out there on the wings as I tootled along through the sky. I always wondered what the throttle body was connected to... Thanks for clearing that up!
I'm a retired USAF officer with 2,400+ flight hours and an aero engineering degree from Virginia Tech.
You have yourself a nice day!
Cyrus said:During those 2,400+ hours, were you designing jet engines? That is not to say we don't appreciate your service or your piloting knowledge, but please do not think that means you outclass Fred in jet engine design - it's a bit rude, to say the least.
minger said:To bring another discipline in here, I'm not so sure a single spool would be possible mechanically. Problems arise as it is seeing pressure ratios in the teen range. That's a lot of force to put on the blade roots...
minger said:From what I understand, reaction water turbines are typically only used in low head appliactions. I doubt they rotate anywhere near the speed that gas turbines do either.
I could fly by flapping my arms if I really wanted to. It would be very practical or efficient, but it could work.
From what I read, no one is asserting that one is proposing a single-stage compressure design with a high compression ratio. However, I believe one asserted that it is possible. Please provide an example of such an axial compressor, or failing that, please provide the equation for such a compressor.mugaliens said:I'm flummoxed by your, Fred's, and others' errant belief that I am in any way proposing single-stage designs, particularly given my oft-repeated "possible, but not practical" mantra.
However, I am equally opposed to the hip-shooting "nope, can't be done" engineering nonsense that's been shoveled into this thread. What part of "possible, but not practical" are you and others failing to understand? Are you errantly believing I'm proposing single-stage designs?
I'm not so sure it is "easy". Please provide an example or the equations for an axial compressor stage.mugaliens said:In a one-stage design, achieving a 20:1 compression ratio is "easy": just increase the velocity.
At which point, it is no longer a reaction turbine, it's an impulse turbine. They can use high head application, but like you said, you're using water momentum, not pressure to drive the blades. Because the wheel is spinning at 1/2 speed of the water jet, the actual force on the blades is not astonomical.mugaliens said:Due to the momentum and viscosity of water, they do not need to.
Simply saying "It can be done" doesn't either.Well this is a rather inane remark. Since you chose not to address the science/physics/engineering issue directly,
There's a big difference between not practical and not doable. There is reason behind one. It's not practical to drive a Hummer. However, if I have the money to do so and feel the need to look cool, why the hell not?I'm flummoxed by your, Fred's, and others' errant belief that I am in any way proposing single-stage designs, particularly given my oft-repeated "possible, but not practical" mantra.
Astronuc said:There are numerous design constraints such at the blade tip speed and the speed of sound in the compressed air. The back pressure on a single stage with a compression ratio of 20:1 would be enormous and the rotation of the flow would seem to be problematic.
Please demonstrate that it is possible, or at least provide the equation for the compression ratio of a single compressor stage for an axial flow.mugaliens said:At 280 psi, it would have to be driven beyond mach. I never claimed one was ever designed, much less built. I merely stated it was possible.
Astronuc said:Please demonstrate that it is possible, or at least provide the equation for the compression ratio of a single compressor stage for an axial flow.
A spool system in a compressor is a type of mechanical arrangement where a series of rotating discs, known as spools, are stacked on a central shaft. As the shaft rotates, the spools also rotate, drawing in and compressing air or gas through the gaps between the spools.
A spool system in a compressor works by using the rotating motion of the spools to draw in air or gas from the atmosphere and then compress it in the gap between the spools. This compressed air or gas is then directed to the outlet of the compressor for further use.
There are several advantages of using a spool system in a compressor, including:
While spool systems have many advantages, they also have some limitations, including:
Spool systems are commonly used in various industries for compressing air or gas, including: