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The boundary layer (in the outer core) between the core and the mantle is known to be thin, with the nominal value about 0.11 meters. The presence of turbulence in the boundary layer has been proposed as a mechanism to explain the observed damping of the Free Core Nutation (FCN). However, the small amplitude of FCN makes the turbulence scenario unlikely. A recent study shows that the precession-driven flow is at the margin of turbulence. Here, we use a local Cartesian box model to study numerically the boundary layer. Our numerical results show that the boundary layer at certain latitudes is not turbulent. By considering the total dissipation in the boundary layer, we find an increase by a factor of 1.86 compared to the laminar solution, implying that the effective viscosity is increased by a factor of 3.5. This may have implications for the chemical interaction occurring at the core-mantle boundary., The 28th IUGG General Assembly (IUGG2023) (Berlin 2023)