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Hub AI
Pogo oscillation AI simulator
(@Pogo oscillation_simulator)
Hub AI
Pogo oscillation AI simulator
(@Pogo oscillation_simulator)
Pogo oscillation
Pogo oscillation is a self-excited type of vibration in liquid-propellant rocket engines caused by combustion instability. The unstable combustion results in variations in engine thrust, causing variation in the acceleration exerted upon the vehicle's flexible structure, which in turn causes variations in engine propellant pressure and flow rate, closing the self-excitation cycle.
The name is metaphorical, comparing the longitudinal axis vibration to the bouncing of a pogo stick. Pogo oscillation places stress on the vehicle frame, which can be dangerous if excessive.
NASA Associate Administrator for Manned Space Flight George Mueller explained Apollo 6's pogo oscillation to a congressional hearing:
Pogo arises fundamentally because you have thrust fluctuations in the engines. Those are normal characteristics of engines. All engines have what you might call noise in their output because the combustion is not quite uniform, so you have this fluctuation in thrust of the first stage as a normal characteristic of all engine burning.
Now, in turn, the engine is fed through a pipe that takes the fuel out of the tanks and feeds it into the engine. That pipe's length is something like an organ pipe so it has a certain resonance frequency of its own and it really turns out that it will oscillate just like an organ pipe does.
The structure of the vehicle is much like a tuning fork, so if you strike it right, it will oscillate up and down longitudinally. In a gross sense it is the interaction between the various frequencies that causes the vehicle to oscillate.
In general, pogo oscillation occurs when a surge in combustion chamber pressure increases back pressure against the fuel coming into the engine. This reduces fuel flow and thus chamber pressure. The reduced chamber pressure in turn reduces back pressure at the fuel pump, causing more fuel to come in and repeating the cycle. In this way, a rocket engine experiencing pogo oscillations is conceptually operating somewhat like a pulsejet or pulse detonation engine.
If the pulse cycle happens to match a resonance frequency of the rocket, dangerous oscillations can occur through positive feedback, which can, in extreme cases, tear the vehicle apart. Other situations that can induce fuel pressure fluctuations include flexing of fuel pipes.
Pogo oscillation
Pogo oscillation is a self-excited type of vibration in liquid-propellant rocket engines caused by combustion instability. The unstable combustion results in variations in engine thrust, causing variation in the acceleration exerted upon the vehicle's flexible structure, which in turn causes variations in engine propellant pressure and flow rate, closing the self-excitation cycle.
The name is metaphorical, comparing the longitudinal axis vibration to the bouncing of a pogo stick. Pogo oscillation places stress on the vehicle frame, which can be dangerous if excessive.
NASA Associate Administrator for Manned Space Flight George Mueller explained Apollo 6's pogo oscillation to a congressional hearing:
Pogo arises fundamentally because you have thrust fluctuations in the engines. Those are normal characteristics of engines. All engines have what you might call noise in their output because the combustion is not quite uniform, so you have this fluctuation in thrust of the first stage as a normal characteristic of all engine burning.
Now, in turn, the engine is fed through a pipe that takes the fuel out of the tanks and feeds it into the engine. That pipe's length is something like an organ pipe so it has a certain resonance frequency of its own and it really turns out that it will oscillate just like an organ pipe does.
The structure of the vehicle is much like a tuning fork, so if you strike it right, it will oscillate up and down longitudinally. In a gross sense it is the interaction between the various frequencies that causes the vehicle to oscillate.
In general, pogo oscillation occurs when a surge in combustion chamber pressure increases back pressure against the fuel coming into the engine. This reduces fuel flow and thus chamber pressure. The reduced chamber pressure in turn reduces back pressure at the fuel pump, causing more fuel to come in and repeating the cycle. In this way, a rocket engine experiencing pogo oscillations is conceptually operating somewhat like a pulsejet or pulse detonation engine.
If the pulse cycle happens to match a resonance frequency of the rocket, dangerous oscillations can occur through positive feedback, which can, in extreme cases, tear the vehicle apart. Other situations that can induce fuel pressure fluctuations include flexing of fuel pipes.