A study of turbulence structure and large-scale motion in the Ekman layer through direct numerical simulations

Direct numerical simulations (DNSs) of the turbulent Ekman layer over a smooth. at surface were performed. The Reynolds numbers Ref (=G/root((nuf)/2)) of 400, 510, 600 and 775 were chosen, where G is the geostrophic wind velocity, nu the kinematic viscosity and f the Coriolis parameter. A large computational box and a long averaging time were employed to capture the turbulence structure and the inertial oscillation. A unique turbulence structure was found in the region where the mean velocity reached its maximum, whereas the well-known streak structure appeared in the vicinity of the wall. Detailed characteristics of the turbulence structures have been discussed using the obtained instantaneous flow field and statistics such as the premultiplied energy spectra and the two-point correlations. The effect of turbulence structure on the turbulence statistics is also examined. At the same time, inertial oscillation is detected in the upper region. Its existing area and comparison with the analytical solution are discussed.