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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. [ABSTRACT FROM AUTHOR]

This work examined the linear instability of a two-dimensional liquid film on an oscillating plane theoretically in the presence of a static electric field perpendicular to the plane. The liquid was considered to be viscous and perfectly conducting, while the gas was considered to be viscous and dielectric. The viscous potential theory and Floquet theory were adopted to obtain the dispersion equation. The influences of electric field intensity, forcing amplitude, forcing frequency, and viscosity were obtained. The results showed that with there is more than one instability region with a non-zero forcing amplitude. The first instability region is called inherent instability, which is due to the electric force overcoming the viscous dissipation, surface tension, and gravity, while the other regions are due to the parametric instability induced by the oscillating plane, forming famous Faraday waves. It was found that increasing the forcing amplitude stabilizes the inherent instability but has a destabilizing impact on Faraday waves. In addition, the increase in the electric field intensity and forcing frequency enhances the inherent instability but has a complex impact on the Faraday waves, depending on the intensity of the viscous dissipation, which is approximately proportional to the square of the wavenumber. [ABSTRACT FROM AUTHOR]