STUDY OF DROPLET MOTION AND WATER FILM FLOW CHARACTERISTICS ON SUPERHYDROPHOBIC SURFACES UNDER AIRFLOW SHEARING

Commercial aircraft are typically equipped with icing protection systems to solve the icing problem, and thermal protection systems are the most common icing protection systems. The thermal protection systems are typically in a wet anti-icing condition, where unevaporated liquid water flows as a water film over the surface under the shear of the airflow. With the widespread use of superhydrophobic materials, researchers are increasingly interested in the use of superhydrophobic materials and thermal protection systems together for anti-icing purposes. The water film flow on superhydrophobic surfaces is quite different from that on conventional surfaces, and the study of droplet motion and water film flow processes on superhydrophobic surfaces can enhance the understanding of the anti-icing mechanism on such surfaces. The test platform for studying droplet motion and water film flow was constructed using a small wind tunnel. A high-speed camera was used to record the droplet motion and water film flow process on the surface of various materials, while the wind speed was adjusted using a variable frequency fan. In the droplet motion test, the droplet motion morphology of the superhydrophobic surface showed minimal difference from the initial state. The total droplet motion time significantly decreased with increasing droplet volume in the range of 10ìL to 40ìL, while the difference in total droplet motion time significantly decreased with increasing droplet volume in the range of 40ìL to 80ìL. In the water film flow test, the water film on the superhydrophobic surface cannot completely cover the test surface. In the low-flow state, the water film thickness was greater and clustered in the middle position due to the weak airflow shear force. After the wind speed gradually increases, the airflow shear force intensifies, causing the water film on the superhydrophobic surface to only sustain a small continuous water film at the initial position, which will quickly break during the development process. Due to the low adhesion of water on superhydrophobic surfaces, the process of water film rupture causes droplets to detach from the water film and break into smaller droplets when exposed to airflow, accelerating them away from the surface. The significant difference in the water film flow characteristics between superhydrophobic surfaces and conventional surfaces is the large number of droplets flying away. The research results can provide a reference for further research on the anti-icing characteristics of superhydrophobic surfaces.