Pulsating primary breakup in dual gas-assisted annular liquid sheets

This study investigates pulsation phenomena for dual gas-assisted annular sheet nozzles, employing air and water as working fluids. Three nozzle configurations with varying liquid sheet thickness were examined experimentally utilizing high-speed imaging of the primary sheet breakup, complemented by CFD analyses to clarify the underlying physical mechanism for the observed pulsation. Numerical results revealed that the pulsation originates from liquid-sheet pinching induced by the outer gas stream, causing pressure buildup within the central gas flow and subsequent radial expansion of the liquid sheet. Experimental results obtained over a broad range of operating conditions show that increasing either inner or outer gas velocity, or liquid velocity, generally increases the pulsation frequency, whereas increasing liquid sheet thickness leads to a decrease. Based on the experimental data, an empirical correlation for calculation of the pulsation frequency as a function of the major operating parameters was proposed. However, the pulsation frequency is primarily governed by liquid sheet thickness and liquid velocity.