Direct numerical simulation and analysis of instability enhancing parameters in liquid sheets at moderate Reynolds numbers

Direct numerical simulations based on the volume-of-fluid method have been performed in order to identify the influence of the inflow velocity conditions on the sensitivity of primary breakup phenomena. A liquid sheet ejected into a gaseous environment at moderate Reynolds numbers ranging from $Re=3000$ to 7000 was considered. The numerical setup allows to vary the influencing parameters individually such that numerical simulations can be performed as “numerical experiments” by varying each of the possible parameters separately. The focus of the present study was directed to the identification of those parameters that most strongly enhance primary breakup phenomena. These key parameters are the flow quantities such as the range of the inflow velocity and the inherent character of the mean velocity profile as well as the corresponding dimensionless groups and turbulence quantities of the nozzle flow. The present results show that in addition to these well known quantities the kinetic energy flux, which depends on the character of the mean velocity profile generated by the nozzle geometry, has a drastic influence on the instabilities appearing. Detailed insight into the flow phenomena is given, such as the velocity profile relaxation and the development of shear layers as well as the spreading rates appearing depending on the inflow velocity conditions. In addition, the influence of the spatial resolution as well as the influence of a simplified two-dimensional compared to a three-dimensional setup has been investigated. The outcome of different mean velocity profiles at the inflow is compared by analyzing the typical kinetic energy and spreading rate issued by different nozzle designs.