Microgravity Research on Liquid Jet Instability
- Paper number
IAC-05-A2.7.08
- Author
Mr. Akira Ihara, Nagoya University, Japan
- Coauthor
Prof. Akira Umemura, Nagoya University, Japan
- Year
2005
- Abstract
Liquid atomization technology is a key to control spray combustion. However, the understanding of turbulent atomization mechanism is not enough although many researchers have spent a lot of time and efforts. This is because the involved elemental processes which occur on very small scales and at high speeds, are difficult to observe in detail. To overcome this difficulty, we have developed a new approach to the turbulent atomization mechanism. It utilizes a liquid jet with near-critical-mixing surface in microgravity, a new experimental environment that no one has used in the past liquid atomization researches.
Characteristic to the turbulent atomization consists of two processes: (1) surface tension-associated destabilization of an issued laminar liquid jet and (2) disintegration of liquid ligaments at the condition of gas Weber number nearly equal to unity. When a liquid is issued into an otherwise quiescent gas at a high pressure exceeding the critical pressure of the liquid, the liquid has the surface which is close to the critical mixing condition. In this condition, small surface tension and large gas-to-liquid surface density ratio enable us to observe the scaled-up, large-Weber-number instability behaviors at low jet speeds, if the flow is not disturbed by gravity forces.
We found that the instability of a circular liquid jet changes drastically at a certain value of pressure, Pt, when the gas pressure is increased at a fixed jet speed. (i) When the gas pressure is smaller than Pt, the issued liquid surface starts to be rapidly distorted at immediately downstream of the nozzle exit, leading to short-wavelength breakup at a short distance from the nozzle exit. The breakup mechanism was revealed experimentally and theoretically on the basis of the microgravity observation. (ii) When the gas pressure is higher than Pt, the issued liquid keeps the laminar flow flows until the hydrodynamic instability is excited far apart from the nozzle exit. Considering the origin of this instability transition, we could gain insight into the excitation mechanism of Rayleigh-Taylor instability at the nozzle exit at the gas pressure less than Pt.
- Abstract document
- Manuscript document
IAC-05-A2.7.08.pdf (🔒 authorized access only).
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