10157 2026 eng 1 38 article AIP Publishing Physics of Fluids 1 2026-01-14 -- -- The Kelvin-Helmholtz instability arises at the interface between two fluid layers with a tangential velocity discontinuity, significantly impacting the safety of systems in industrial applications. Despite extensive studies, many theoretical analyses neglect viscosity and frictional drag due to the complexity of solving the dispersion equation. However, including these effects is crucial, as viscosity alters the growth rate of the instability, while frictional drag influences energy dissipation and momentum transfer. In this study, these effects are incorporated into both finite and infinite flows. The assumption of a potential flow combined with a dissipation method is employed to derive the dispersion equation, providing a more tractable approach than direct calculation methods. The results indicate that, in the case of infinite flows, the frictional drag suppresses the growth of the instability for long waves (small wavenumber k) but enhances it for short waves (large k). In contrast, the surface tension dominates, while the frictional drag only slightly affects the growth rate in the case of finite flows bounded by solid walls. Physics of Fluids 10.1063/5.0306177 yes Physics of Fluids 2025-12-15 Mako Sato Thi Thai Le Thorsten Koch Thi Thai Le Koch, Thorsten MODAL-Gesamt Le, Thi Thai MODAL-EnergyLab Applied Optimization https://opus4.kobv.de/opus4-zib/files/10157/Frictional_drag_KHI.pdf