Linear stability of viscoelastic confined liquid jet in the presence of gas velocity oscillations

This work examines the linear instability of a viscoelastic confined liquid jet as the acoustic oscillations are taken into consideration, which is expressed as the oscillatory gas velocity, and this theoretical problem is solved using the Floquet theory. The unstable regions are dominated by capillary instability, Kelvin-Helmholtz instability (KHI), and parametric instability, and the impact of heat and mass transfer in the different unstable regions is also discussed. In addition, the different instability mechanism for different azimuthal wavenumbers is found. Because of its viscoelasticity, the liquid jet is more unstable than its Newtonian counterpart. In addition, the influence of the constant time ratio, Reynolds number, and elasticity number is more dramatic on the parametric instability than that on the KHI. The forcing frequency impacts the parametric instability mainly by changing corresponding wavenumber of parametric unstable region. Furthermore, a novel phenomenon is that heat and mass transfer has a complex effect on KHI and parametric instability, depending on the increase extent of aerodynamic force induced by mass transfer. For a smaller density ratio between gas and liquid, heat and mass transfer enhances KHI and parametric instability. Moreover, the increase in the density ratio and Weber number can enhance the interfacial instability and expands the unstable wavenumber range.