Study of the Modes Responsible for the Breakup of High-Speed Cylindrical Jets Injected into a Quiescent Gas*

The current study involves understanding the modes observed in the breakup of high-speed cylindrical jets using mean flow linear stability analysis and volume of fluid (VoF) simulations. Previous studies on the breakup of high-speed rectangular liquid sheets have shown the development of large wavelength sinuous modes, which are dominant at high gas shear layer thickness, leading to the complete breakup of the sheet. In addition, the perturbation kinetic energy in gas is dominant for the spatially growing sinuous mode. Extending the work to 3D cylindrical geometry, mean flow linear stability analysis shows that the helical (asymmetric) modes shift to higher wavelengths than the axisymmetric modes when the gas shear layer thickness is increased. The shift to higher wavelengths is also accompanied by the dominance of perturbation kinetic energy in gas compared to that in the liquid. Volume of Fluid simulations are performed for the high-speed cylindrical jets to observe the manifestation of perturbations in the non-linear regime leading to the complete breakup of the liquid jet. The VoF simulations show that the complete fragmentation of the jet is caused by large-wavelength helical modes, accompanied by a significant increase in gas shear layer thickness.