Numerical study on the breakup mechanisms and characteristics of liquid sheets

The pre-film breakup in a high-performance gas turbine combustor is simplified into a two-dimensional and three-dimensional liquid sheet breakup, and the liquid sheet breakup processes, mechanisms and characteristics are investigated under nearly representative operating conditions. First, the two-dimensional flat liquid sheet breakup processes are simulated using a Reynolds-averaged Navier-Stokes (RANS) model and a VOF (volume of fluid) method. The effect of airflow velocity on the liquid sheet breakup distance is analyzed under various high-speed airflow velocities of 80 m/s, 180 m/s and 280 m/s. Then, the three-dimensional liquid sheet breakup processes are simulated using the large eddy simulation (LES)/VOF method, and the variations of the characteristics of both the horizontal liquid sheet and the oblique liquid sheet, such as the breakup process, breakup mode, breakup distance, wave characteristics and liquid sheet thickness, are analyzed. It's found that for the two-dimensional flat liquid sheet breakup, the liquid sheet breakup distance decreases with the increase of airflow velocity or Weber number (We). When the airflow inlet velocities are 80 m/s (We = 6.13), 180 m/s (We = 220.5) and 280 m/s (We = 741.13), the liquid sheet breakup distances are 22.2 mm, 16.0 mm and 10.5 mm, respectively. An empirical formula of the liquid sheet breakup distance was thus summarized. For the three-dimensional liquid sheet breakup, as the airflow inlet angle increases, the breakup distance is significantly shortened, which is 2.21 mm at 0 degrees and 1.85 mm at 15 degrees, and the oscillation angle of the liquid sheet becomes larger. For the oblique liquid sheet breakup, the liquid sheet breakup mode becomes more complicated and the surface wave fluctuation amplitude increases. The empirical formula prediction values of the liquid sheet breakup distance developed in this study are in good agreement with the numerical results.