experimental study on self-pulsation of a gas/liquid swirl coaxial injector in high pressure environment
- Paper number
IAC-09.C4.8.9
- Author
Mr. Ji-Hyuk Im, Seoul National University, Korea, Republic of
- Year
2009
- Abstract
The effects of the ambient pressure on self-pulsation characteristics of a gas/liquid swirl coaxial injector are studied experimentally. Self-pulsation has strong influences on the atomization and mixing process and accompanies strong noises. A strong pressure and flow rate oscillation are detected when self-pulsation occurs. This unstable phenomenon can generate the heat release oscillation in combustion chamber of liquid rocket engine and intensive noise can provide harmful disturbances to combustion instability. A sharp and narrow increase in frequency spectrum by self-pulsation is observed at a certain frequency. Core swirling liquid and surrounding annular gas injector was design. A gas/liquid swirl coaxial injector was mounted in the high pressure chamber and the ambient pressure was increased up to 10 bar. The liquid and gas velocity were varied as an operating parameter and recess length was varied as an geometric parameter. The spray patterns were investigated according to the ambient pressure using digital camera and stroboscope. The spray patterns are compared with the results in the atmospheric conditions. The frequency spectrum of strong noise and spray oscillation by self-pulsation was obtained using acoustic device and laser diagnostics technique. To identify the mechanism of self-pulsation, the unstable wave of the liquid sheet was observed and the dominant frequency of the liquid sheet was measured by He-Ne laser and photo detector. From the results, it is found that the ambient pressure has great effects on self-pulsation and the increase of the ambient pressure suppresses self-pulsation phenomena. The frequency of the spray oscillation is the same with the acoustic frequency of the noise and all frequency range is from 2 to 4 kHz. Also, the self-pulsation boundary is obtained according to injection conditions for various recess length. The liquid phase momentum plays a role of the inertial element against self-pulsation and the gas phase momentum induces self-pulsation. The increase of the recess length widens the self-pulsation region. The dominant frequency of the liquid sheet is proportional to the liquid Reynolds number. From proper assumptions, self-pulsation frequency can be normalized with the dominant frequency and it is found that self-pulsation occurs due to the unstable wave of the liquid sheet and its frequency is determined by the dominant frequency of the liquid sheet.
- Abstract document
- Manuscript document
IAC-09.C4.8.9.pdf (🔒 authorized access only).
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