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Breakup Length of Planar Liquid Sheet with Cocurrent Air Flows
( Ryota Kawabata ),( Ippei Oshima ),( Shingo Nishiyama ),( Akira Sou ),( Kazuaki Matsuura ) 한국액체미립화학회 2017 한국액체미립화학회 학술강연회 논문집 Vol.2017 No.-
Air blast atomizer has been employed in a combustor of gas turbine engine. To reduce NOx emissions from a gas turbine, breakup and dispersion of a liquid fuel sheet with cocurrent air flows injected from the air blast atomizer have to be controlled. If we can predict the breakup length of the oscillating liquid sheet, we can estimate and control the spray characteristic in the combustor. When the liquid sheet is exposed to high-speed air flows, it oscillates by the Kelvin-Helmholtz instability, and then thin liquid bags are formed by the Rayleigh-Taylor instability. We define the breakup length as the distance from the nozzle exit to the point where the bags rupture to be a fine spray. In our previous research, we investigated the effects of air and liquid velocities, liquid fluid properties, and gas density on the breakup length. We divided the breakup process into two phases. The first phase is the period largely affected by K-H instability, and the second phase is the period from the onset of bag formation to the bag rupture. We proposed the correlations on the time t<sub>1</sub> and t<sub>2</sub> for each phase. In this paper, we perform a number of additional visualization experiments of the atomizing liquid sheets under different conditions in order to investigate the effects of liquid film thickness D<sub>L</sub>, width D<sub>Lip</sub> of the atomizer lip on the breakup length, and propose new correlations on the time t<sub>1</sub>, t<sub>2</sub> which take into account the effects of D<sub>L</sub> and D<sub>Lip</sub>. In addition, we clarified that the wave velocity V<sub>w</sub> is proportional to the air velocity and the square root of the density ratio of gas to liquid. Finally, the estimated breakup length is confirmed to be in good agreement with the measured data.