ID 388

Dynamics of a Spatially Developing Liquid Jet with Coaxial Gas Flow

 

Abstract:

A three-dimensional round liquid jet within a low-speed coaxial gas flow is numerically simulated and analyzed via vortex dynamics. The evolution of instabilities on the liquid-gas interface is correlated with the vortex interactions near the interface. Two types of surface deformations are distinguished: First, those near the jet start-up cap are encapsulated inside the recirculation zone behind the cap. These deformations are directly related to the dynamics of the growing cap and can be explained by the vortices that are generated right behind the cap. The second kind of deformations occurs farther upstream of the cap and are mainly driven by the gas shear which triggers a Kelvin-Helmholtz (KH) instability. The three-dimensional deformation of the axisymmetric KH vortices then leads to several liquid lobes. These lobes stretch first as thinning sheets and then, based on the type of vortex interactions, either continue stretching into elongated ligaments or thin further and tear to create liquid bridges and holes. The different behaviors depend on Weber and Reynolds numbers. This second type of deformation is best portrayed in a frame moving with the convective velocity of the liquid jet. Comparison of our spatial analysis with the temporal studies in the literature show the reliability and consistency of those temporal analyses.