Experimental exploration of free-surface turbulence

Free surface flows are complex, multiphase and multiscale flow regimes with great interest for naval hydrodynamics (e.g., white water behind ships). Interfacial transport, mixing and bubble entrainment are some of the physical processes present in this environment that still need attention experimentally to validate Computational Fluid Dynamics (CFD) solvers and fill gaps or assumptions in existing models. Generating free-surface turbulence (FST) in a lab is not a trivial process, especially when needed to fulfill specific flow requirements and reach turbulence levels that up to date had been unexplored experimentally. In this study we discuss challenges and practices to generate homogeneous isotropic turbulence (HIT) in an open-box facility that can reach strong turbulence levels to capture bubble entrainment events. We will discuss turbulence statistics in a large region in the vicinity of the free surface to characterize the facility, and we will explore how turbulence levels can affect turbulence statistics to challenge the energy redistribution mechanism imposed by the kinematic boundary condition at the surface. Finally, we will discuss additional challenges that arise in strong FST and practices to tackle them during data acquisition.