Abstract
Self-excited high frequency combustion instability (HFCI) of first-order tangential (1T) mode was observed in a staged-combustion LOX/Kerosene liquid rocket engine numerically. Two different kinds of 1T patterns, standing wave mode and traveling wave mode, were captured in the present work. In the nominal operation condition, the ratio of oxygen-to-fuel (O/F) was 2.5. Propellant was evenly distributed in all injectors and no HFCI occurred. The chamber pressure obtained from the numerical simulation and experiment showed a good agreement, which validated the numerical model. When the mass flow of fuel for two injectors was modified, severe HFCI occurred. The pressure wave node was located at a fixed diameter, showing a 1T standing wave mode. As the O/F was set 4.4 and the propellant distribution was completely uniform, the numerical result yielded a 1T wave node featured a spinning behavior, which was a traveling 1T wave mode. Once the HFCI arose, no matter what standing mode or spinning mode, the pressure and heat release oscillated totally in phase temporally and coupled spatially. The heat release from combustion was fed into the resonant acoustic mode. This was the thermoacoustic coupling process that maintained the HFCI.
Highlights
high frequency combustion instability (HFCI) remains an unresolved problem for the development of liquid rocket engines (LREs)
The results indicated that combustion instability was associated with periodic vortex shedding
From the numerical simulation results and analysis above, the following three conclusions were reached: 1. HFCI is sensitive to initial conditions
Summary
HFCI remains an unresolved problem for the development of liquid rocket engines (LREs). Urbano et al (2016) conducted a corresponding high-fidelity calculation, which is a landmark work for its high accuracy and enormous computing load Both the experimental analysis and numerical results indicated that the 1T mode thermoacoustic instability was strongly coupled with oxidizer injectors. The pressure-time trace indicates that it is an equalamplitude oscillation, and the dominant frequency is 3738 Hz. The chemical equilibrium acoustic velocity is 1092.2 m/s, calculated by CEA, so the theoretical 1T frequency is 3556 Hz. The error between the numerical and theoretical values is 4.8%. A conclusion can be drawn that it is a spinning 1T HFCI mode and the direction of rotation is counter-clockwise The pressure and heat-release coupling process drives the HFCI
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