Abstract: The influence of topography on rotating fluids may exceed conventional expectations. Here, we numerically examine viscous incompressible flows induced by sidewall topography, confined within a modified cylinder that rotates rapidly about its central vertical axis and precesses about another axis. To investigate specific flow patterns and boundary-interior correspondences, the cylindrical sidewall is modified by adding a vertical fin-type barrier extending all the way from the bottom to the top. The fully nonlinear Navier−Stokes equations with precessional forcing are solved in this modified cylindrical geometry, using a mixed finite element method. Numerical results show that the introduction of sidewall topography significantly alters the precessionally driven flow, particularly at high precession rates. While the primary dynamics associated with inertial wave propagation persist, rich vortical structures and turbulence emerge. Interestingly, the barrier does not invariably suppress the kinetic energy density; when its height approaches the cylinder radius under strong precession, the kinetic energy density even exceeds that of the cylinder case without a barrier. Such an anomalous enhancement of kinetic energy may offer new insights into how precession-driven flows over topography could contribute to sustaining long-lived planetary magnetic fields, including that of the early Moon.