E-MPS法を用いた薄膜を有する壁面に対する水滴衝突による二次液滴の数値シミュレーション

Abstract

The ice accretion on an aircraft threatens navigation safety because it causes deformation of the wing shapes and reduces the aerodynamics performance. In the glaze ice conditions, where the ambient temperature is about -10 to -3 ℃, impinged droplets do not freeze instantly, and they runback along the wing surface as a liquid film. In addition, splashing and rebounding occur, which generate secondary droplets, if supercooled large droplets (SLD) whose diameters are more than 40 μm impinge on an aircraft. Furthermore, liquid film on an aircraft wing at glaze ice conditions significantly affects these phenomena. The purpose of this study is to model the droplet impact behavior and the formation of secondary droplets on a wall with a thin water film in terms of SLD icing under glaze ice conditions by using the three-dimensional E-MPS method. In a vertical impact case, the crown is formed by the impingement, and no secondary droplet is generated by the finger jets. The crown height decreases with decreasing water temperature, which is attributed to the decrease in Weber number. In an oblique impact case, the total mass of secondary droplets increases as the impact angle decreases. The secondary droplet mass generation attains the maximum at about 39 degrees impact angle. Moreover, the secondary droplets do not appear as the impact angle decreases around 30 degrees, resulting from Kelvin-Helmholtz instability. The velocities of secondary droplets decrease as the secondary droplets are generated later.