Direct numerical simulation of a high-Froude-number turbulent open-channel flow

In this study, we successfully conducted a direct numerical simulation of a high-Fr turbulent open-channel flow at a Froude number of 1.8 and a Reynolds number of 2325 based on bulk velocity, gravitational acceleration, water depth, and kinetic viscosity, using the multi-interface advection and reconstruction solver (MARS). We confirmed that typical wall-bounded turbulent structures were observed in this high-Fr open-channel flow. On the other hand, near free-surface, surface deformations are constituted of large-scale gentle bumpy waves with the maximum wave height corresponding to approximately 4% of the water depth and small-scale isotropic waves on the large-scale waves. The large-scale waves would generate the high-speed streaky structures near the free-surface and the scale of the small waves would be equivalent to the near free-surface turbulent kinetic energy. Near the free-surface, wall-normal turbulent intensity and energy-dissipation rates increase toward the free-surface, and the tendencies of...