Experimental study of shear-driven water film with brightness-based laser-induced fluorescence technique

Abstract

Driven by low-temperature and high-speed airflow, the water droplets impinging the surface of the aircraft will gather into water film, affecting the aerodynamic characteristics and endangering flight safety. In this paper, a high-speed video system with the brightness-based laser-induced fluorescence (BBLIF) technique was used to analyze the transient water film thickness and wavy characteristics on a horizontal metal plate. A series of experiments were performed over a wide range of wind speeds (15.59 m/s ∼ 52.20 m/s) and water volume flow rates (100 ml/min ∼ 900 ml/min). According to the interfacial phenomena observed in the experiment, the water film flow is classified into five regimes: two-dimension-wave, ripple-wave, dual-wave, roll-wave, and entrainment. The water film characteristics such as mean film thickness, film roughness, wave frequency, and rolling wave intermittency are studied under the influences of air velocity and water flow rate. The results show that the complex fluctuation characteristics of water film are the result of the joint action of surface tension, interfacial shear force and inertia term of water film, and are closely related to the water film flow regime. The findings could contribute to a better understanding of the shear-driven water film wavy characteristics and the optimization of the anti-icing or de-icing system.