Surface wave and splashing of liquid film by oblique water jet impinging on a vertical plate

Liquid film cooling by jet impingement, known as a common thermal protection technique, is extensively applied in liquid rocket engines. The present work investigates the impact of a water jet onto a vertical plate by highspeed visualization system and laser particle analyzer, with a focus on the characteristics of surface waves and droplets splashing during the formation of liquid film. Depending on whether the jet is broken before impact, two regimes are identified, i.e., droplet or continuous jet impingement regime. The frequency and velocity of the surface wave and the splashing rate are jointly affected by the jet angle and the impingement distance. The splashing is mainly caused by the capillary breakup of the crown film that forms at the edge of the surface wave, and most of the splashing droplets are generated from the top of the crown film. The larger the jet angle, the smaller the wave frequency and velocity, but the higher the splashing rate. A large impingement distance causes a small wave frequency and velocity due to the shift of the impingement regime, further resulting in different tendencies in the splashing rate. A parameter expression for the size distributions of splashing droplets is established by the fitting result of the log-normal distribution and the Rosin-Rammler (R-R) distribution, where the parameters are associated with the jet Weber number.