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In this study, the standard unsteady vortex lattice method (UVLM) is modified by different approaches to accommodate the viscous effects on the flow field and lift force history of a moving airfoil. Firstly, the conventional inviscid vortices are replaced with ones that satisfy Oseen’s approximation of the Navier–Stokes equations. These are known as viscous vortices and are a function of the Reynolds number. Compared to the standard UVLM, the results show a different behavior for the wake deformation at lower Reynolds numbers where the viscous effects are more dominant. The second modification is implemented by an elegant alteration in the conservation of circulation condition based on the fact that the whole domain composed of the fluid and solid can be treated as a single kinematic entity. The no-slip boundary condition enables considering the moving solid vorticity in the Kelvin condition, where the results for the frequency response indicate more phase lag compared to the standard UVLM or potential flow theories (i.e., Theodorsen), which increases at higher reduced frequencies. Furthermore, the effect of the position of the shed vortices is analyzed and seen to affect the amplitude of the resulting lift history. Finally, the no-slip boundary condition is also explicitly considered by implementing source singularities along the surface of a thick airfoil, resulting in a better prediction of the lift magnitude compared to CFD results. The combination of all the aforementioned modifications has the potential to enhance the performance of the UVLM in case of viscous flows at relatively high reduced frequencies.