Main Injector Assembly

Spark igniter

Fluted oxidizer posts where hot hydrogen evaporates the oxygen

Thrust load

Oxygen

FIGURE 9-6. Main injector assembly of the Space Shuttle main engine showing baffle with five outer compartments. (Courtesy of The Boeing Company, Rocketdyne Propulsion and Power.)

Spark igniter

Fluted oxidizer posts where hot hydrogen evaporates the oxygen

Oxygen inlet manifolds ^

Thrust load transmitting . cone

Oxygen from main' oxygen valve

FIGURE 9-6. Main injector assembly of the Space Shuttle main engine showing baffle with five outer compartments. (Courtesy of The Boeing Company, Rocketdyne Propulsion and Power.)

Various mechanisms of energy absorption or vibration damping exist in a thrust chamber. Damping by well friction in combustion chambers is not significant. The exhaust nozzle produces the main damping of longitudinal mode oscillations; the reflection of waves from the convergent nozzle entrance departs from that of an ideal closed end. The principal damping source affecting propagation in the transverse plane is combustion itself. The great volumetric change in going from liquid to burned gases and the momentum imparted to a particle (solid or liquid) both constitute damping phenomena in that they take energy from high instantaneous local pressures. Unfortunately, the combustion process can generate a great deal more pressure oscillation energy than is absorbed by its inherent damping mechanism.

Acoustical absorbers are applied usually as discrete cavities along or in the wall of the combustion chamber near the injector end. Both act as a series of Helmholtz resonators that remove energy from the vibratory system which otherwise would maintain the pressure oscillations. Figure 9-7 shows the application of discrete cavities (interrupted slots) at the "corner" of the injector face. The corner location usually minimizes the fabrication problems, and it is the one location in a combustion chamber where a pressure antinode exists for all

1 Volume jH Orifice

-L + AL Helmholtz resonator

Spring

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Project Management Made Easy

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