Experiments on a Coaxial Injector Under an Externally-Forced Transverse Acoustic Field (POSTPRINT)
ENGINEERING RESEARCH AND CONSULTING INC (ERC INC) EDWARDS AFB CA
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In order to gain a better understanding of some of the underlying physics associated with the interaction of high-amplitude acoustic waves and a coaxial-jet type injector similar to those used in cryogenic liquid rockets, a non-reacting-flow experimental investigation was conducted under sub-, near-, and supercritical chamber pressures, with and without acoustical excitation. Past research works on this subject have shown both the relevance and importance of geometrical changes in an injectors exit-area and its nearby physical and fluid mechanical processes. On this basis, special attention is paid in collecting spatially-resolved mean temperatures and documenting the aforementioned interactions at the exit of this injector. Short-duration and high-speed digital cameras provided information on the dynamic behavior of this jet. Mean and root mean square RMS values of the coaxial-jet dark-core length fluctuations were measured from the acquired images via a computer-automated method. It is seen that as the outer-to-inner jet velocity ratio increases, the RMS of the dark-core length fluctuations decreases. It is hypothesized that a connection to rocket instability can be obtained from the data analyzed thus far by way of the magnitude of the RMS values of the dark-core length fluctuations. It is possible that decreases in the fluctuation levels, which were shown here to occur at higher velocity ratios, could weaken a key feedback mechanism for the self-excitation process that is believed to drive the combustion instability in rocket engines. This could offer a possible explanation of the combustion stability improvements experienced in engines under higher outer-to-inner jet velocity ratios. Finally, there also appears to be a good correlation between the dark-core length and the outer-to-inner jet momentum flux ratio, but the form of this dependence was found to be different at subcritical pressures than the rest of the chamber conditions.
- Liquid Propellant Rocket Engines
- Test Facilities, Equipment and Methods
- Liquid Rocket Propellants