Gas foil bearings (GFBs) are key components in high-speed rotating machinery due to their low friction, oil-free operation, and thermal resilience. A crucial performance parameter is the lift-off speed, which defines the minimum rotational speed required to fully separate the rotor and the bearing through a gas film. This study presents a time-domain numerical analysis of GFBs using the finite volume method to solve the compressible Reynolds equation, coupled with a nonlinear structural model of the top foil. The model incorporates geometric imperfections through an ovalization foil profile, allowing evaluation of the effects of depth and angular orientation on the rotor’s static and dynamic behavior. Comparisons with a finite difference formulation validate the proposed methodology. The results demonstrate that the ovalization profile significantly alters the static equilibrium position and the rotor’s trajectories, leading to distinct orbital shapes and displacement patterns. Additionally, the lift-off speed may vary by up to 12% depending on the ovalization parameters, highlighting the sensitivity of this performance metric to geometric imperfections. These findings provide valuable insights into the behavior of gas foil bearings under non-ideal geometries and dynamic conditions, contributing to improved design and reliability in high-performance applications.