  The study deals with the breakup behavior of swirling liquid sheets
discharging from gas-centered swirl coaxial atomizers with attention focused
toward the understanding of the role of central gas jet on the liquid sheet
breakup. Cold flow experiments on the liquid sheet breakup were carried out by
employing custom fabricated gas-centered swirl coaxial atomizers using water
and air as experimental fluids. Photographic techniques were employed to
capture the flow behavior of liquid sheets at different flow conditions.
Quantitative variation on the breakup length of the liquid sheet and spray
width were obtained from the measurements deduced from the images of liquid
sheets. The sheet breakup process is significantly influenced by the central
air jet. It is observed that low inertia liquid sheets are more vulnerable to
the presence of the central air jet and develop shorter breakup lengths at
smaller values of the air jet Reynolds number $Re_g$. High inertia liquid
sheets ignore the presence of the central air jet at smaller values of $Re_g$
and eventually develop shorter breakup lengths at higher values of $Re_g$. The
experimental evidences suggest that the central air jet causes corrugations on
the liquid sheet surface, which may be promoting the production of thick liquid
ligaments from the sheet surface. The level of surface corrugations on the
liquid sheet increases with increasing $Re_g$. Qualitative analysis of
experimental observations reveals that the entrainment process of air
established between the inner surface of the liquid sheet and the central air
jet is the primary trigger for the sheet breakup.
