Simulations of Thin Film Dynamics on a Flat Plate and an Airfoil 2019-01-1938

The goal of the present study is to investigate the dynamics of a thin water film on a flat plate and an airfoil using direct numerical simulation (DNS). The first case for a wetted flat plate is used to model former experiments and investigate the dynamics of a wind-driven water film. The second case for a thin film on a NACA 0012 airfoil of chord length 0.5 m is used to investigate the dynamics of a wind-driven water film on a curved surface. Particular attention is paid to the interaction between the liquid film and the air shear-layer above the film. As the incoming airflow moves over the thin water film, instability is triggered at the gas-liquid interface. Interfacial waves develop and are advected downstream. The interaction between the air flow and the interfacial waves induces shedding vortices near the interface, which in turn perturb the liquid film farther downstream. Simulations are performed using the open source multiphase flow solvers, Gerris and Basilisk. Both solvers employ a finite-volume approach and the interface is captured using a Volume-of-Fluid (VOF) method. While the long-term goal of this research effort is to investigate glaze ice formation in water films on airfoils, the current simulations focus on liquid film dynamics starting with a constant thickness exposed to a relatively low flight airspeed. The resulting simulations demonstrate the unsteady film dynamics and thickness evolution and natural waviness generated by the liquid-film and free-stream flow interactions.