The Effects of Froude Number on a Turbulent Boundary Layer with a Free-Surface

We present direct numerical simulations of a temporally developing turbulent boundary layer along a moving flat plate piercing through the free surface. The influence of the Froude number on the results is examined. We confirm the findings in the literature, that the vorticity and secondary flows generated at the free surface for low Froude numbers (\(Fr\sim 0\)) is primarily due to anisotropy of the normal Reynolds stresses. At intermediate Froude numbers however, the vorticity generated at the free surface is related to the curvature of the interface, and is directly injected in the outer and logarithmic portions of the turbulent boundary layer. This has an impact on its overall structure with increased levels of turbulent kinetic energy production. The deformable interface results in changes to the velocity distribution in the near-surface region and loss of self-similarity within the log-law region of the boundary layer.