RESUMO

The liquid core structure in the near-injector dense spray region of pressure-atomized sprays is observed using a laser tomographic imaging technique for Weg of 12 to 85. Small-amplitude instability waves are observed to form on the liquid-air interface with subsequent growth of these waves; and an abrupt disintegration of the liquid core is observed at x/d of approximately 50. The diameter of the liquid core up to this point increases due to the deceleration effect. A relatively small number of droplets is observed near the liquid-air interface as long as the liquid core is intact in comparison to the downstream locations following the liquid core breakdown, which involves the liquid-phase flow field consisting of large ligaments and droplets. This suggests an atomization mechanism dominated by the liquid core breakdown which leads to a rapid secondary atomization of the ligaments and large droplets. The development of the length-scale distribution of the liquid phase is consistent with the above atomization mechanism in that the dominant length scale is that of the liquid core up to x/d of approximately 50, at which point a broadened spectrum in the liquid-phase length scales is observed. Subsequent to the liquid core breakdown, a trend toward smaller length scales, indicative of further atomization, is observed while an equilibrium drop size distribution is not achieved by x/d of 150 in that some presence of ligaments and nonspherical liquid elements is detected at this axial location. Surface wave amplitude and wavelength of the liquid-air interface are also measured using the current tomographic imaging technique for up to x/d of 30, which show that the overall amplitude of the waves grows linearly as a function of axial distance up to x/d of 30 and has similar magnitude for Weber numbers of 12 to 85. The wavelength tends to increase with increasing distance from the injector, and smaller wavelength is observed for higher Weber number.