Destabilization of a planar liquid stream by a co-flowing turbulent gas stream

Abstract

In Airblast atomization, the disintegration of a liquid stream is assisted by a co-flowing high speed gas stream. The shear instability develops at the interface, forming interfacial waves that propagate and eventually break into droplets downstream. In the present study, the destabilization of a planar liquid stream by a co-flowing gas stream with different turbulence intensities is investigated through direct numerical simulation. A parametric study is conducted to investigate the effect of gas inlet turbulence intensity on the interfacial instability near the nozzle exit and the development of two-phase mixing layer downstream. The gas-liquid interface is resolved by a momentum-conserving volume-of-fluid method. A digital filter approach is used to generate temporally and spatially correlated turbulent velocity fluctuations at the gas inlet. The interfacial stability is absolute for all cases considered. The dominant frequency and the spatial growth rate corresponding to the most unstable mode are measured and compared with experiments and spatial-temporal linear stability analysis. The numerical results of the dominant frequencies agree well with the experimental data. Both the dominant frequency and the spatial growth rate increase with the gas inlet turbulence intensity, after passing a threshold value. The linear stability analysis with the turbulent eddy viscosity model captures the increasing trends of the dominant frequency and the spatial growth rate but significantly underpredicts the values. Two-phase turbulence statistics, including Reynolds stresses and turbulent kinetic energy dissipation, are also presented. It is shown that the gas inlet turbulence tends to enhance interaction between the two streams near the nozzle exit and to reduce the interaction downstream.