Turbulence statistics in open-box free surface turbulence

Free surface dynamics are of critical importance in many engineering applications and fundamental physical mechanisms. Surface deformation and gas entrainment can be triggered by turbulence (e.g., breaking waves or submersed jets). However, free surface topography and turbulence characteristics underneath are coupled through a balance mechanism between the disrupting turbulent kinetic energy and the stabilizing surface tension and gravity forces. Despite the great progress in Computational Fluid Dynamics, the effect of this balancing mechanism on the turbulence characteristics is not fully understood yet, mainly due to the lack of experimental evidence for the processes at play. This work introduces a new free surface turbulence facility to generate homogeneous and isotropic turbulence and investigate fundamental energy redistribution and air entrainment in high Reynolds number regimes. Facility design relies on an open-box symmetric configuration inspired by the forced equivalent turbulence boxes. Flow characteristics are investigated in a large region in the vicinity of the free surface by means of particle image velocimetry. Results reveal three main flow zones: a jet merging region, a homogeneous and isotropic core and a free surface influenced zone. We will discuss facility design principals and focus on turbulence statistics in both the free surface influenced, and homogeneous and isotropic regions.