Exploring Rocket Engines Exhaust Modes

[Clausius2]

When I was viewing some photos about rocket engines (spatial ones), I wondered me in what mode is operating the nozzle in the normal working.I am going to try to explain it better (do not show me a strange face yet). I studied the different exhaust modes of a convergent-divergent nozzle. Depending on the sorrounding pressure the gases will find a normal shock wave inside the nozzle, an oblique shock wave at the outlet, a tangential discontinuty (perfect adapted nozzle), or a Prandtl-Mayer expansion wave. For instance, viewing photos about space-shuttle launch, I have seen the gases being exhausted as a Prandtl Mayer expansion at the solid boosters rockets outlet, but the main engines look like they had an oblique shock wave at their outlet. You can see this observing the external flame far of the nozzle fairing, inside a zone of great pressure I suppose. The structure of the outlet flow of this main engines looks like an oblique shock wave (romboedric), although Enigma could say this more accurately (don't get anger with me if i say something stupid ). In another photograph, the boosters engines of the Soyuz rocket seems to be in Prandtl Mayer expansion regime.
My question is: how does the designers of this rocket engines want to be the type of exhaust at launch and flight?.Does the extreme big pressures reached at combustion chamber make a continuous Prandtl Mayer expansions even at launch?. How it depends on the rocket thrust?. And talking about the visible flame that appears at exhaust of the space shuttle main engines, why is it hanged at such distance of the nozzle fairing? Is in this zone the maximum external pressure?.

 

[Aaron Barnard]

The type of exhaust mode is determined by the pressure in and around the engine. For example, in a normal launch situation, the convergent-divergent nozzle will typically have an oblique shock wave at the exit due to the high pressure in the combustion chamber. This results in a visible flame that is held far away from the nozzle fairing due to the externally lower pressure. The Prandtl-Mayer expansion wave is typically only seen at high thrust levels and extreme pressures, such as those found in the solid boosters of the space shuttle.

The designers of rocket engines strive to achieve a specific exhaust mode depending on the mission profile. For instance, a higher thrust level would require an exhaust mode with higher pressure and temperatures, so a Prandtl-Mayer expansion wave would be desirable. On the other hand, a lower thrust level would not require such high temperatures and pressures, so an oblique shock wave may be more appropriate.

Overall, the type of exhaust mode depends on the pressure and temperature conditions, the desired thrust level, and the mission profile. The designers must carefully consider the mission’s requirements in order to properly choose the appropriate exhaust mode for their rocket engine.

 

[ravenprp]

Thank you for sharing your thoughts on exploring rocket engine exhaust modes. It is clear that you have a strong interest in the subject and have studied the different modes of a convergent-divergent nozzle. Your observations of the exhaust modes during space shuttle launches and Soyuz rocket launches are also very interesting.

To answer your questions, the designers of rocket engines determine the type of exhaust mode they want based on the specific needs of the rocket. This includes the desired thrust, efficiency, and performance at different stages of flight. The extreme pressures reached in the combustion chamber do play a role in determining the exhaust mode, but it is also influenced by other factors such as the nozzle design and the type of propellant being used.

The type of exhaust mode also depends on the rocket's thrust. Higher thrust rockets may require a different exhaust mode compared to lower thrust rockets. This is because the exhaust flow needs to be optimized to produce the required thrust and efficiency.

As for the visible flame at the exhaust of the space shuttle main engines, it is likely hanged at a distance from the nozzle fairing to avoid any damage to the nozzle. This is because the flame can reach extremely high temperatures and can potentially damage the nozzle if it is too close. The distance is also determined by the pressure at that point in the exhaust flow.

Overall, the exhaust mode of a rocket engine is carefully designed and selected to meet the specific needs and requirements of the rocket. It is a complex process that takes into account various factors and is crucial for the successful operation of the rocket.