SPREADING MORPHOLOGIES AND FLUCTUATION CHARACTERISTICS OF LIQUID FILM FORMED BY OBLIQUE IMPINGEMENT OF LIQUID JETS ON WALL

To deeply understand the formation and evolution mechanism of surface waves on obliquely impinging wall jets and the different spreading morphologies of liquid films, experimental observations and numerical simulations of oblique impingement of jets on walls are carried out. High-speed cameras record the spreading morphologies of liquid films under different jet velocities and impingement angles, and numerical simulations combined with experimental observations revealed the formation and evolution process of surface waves on the liquid film. The results show that with increasing jet velocity, the spreading morphology of the liquid film will undergo three flow patterns: smooth liquid film with a closed rim, fluctuating liquid film with a closed rim, and fluctuating liquid film with an open rim. The spreading height and width of the film are approximately proportional to the jet velocity, but non-linear changes occur when the liquid film edge breaks up. As the jet impingement angle increases, the spreading of the liquid film changes from narrow to wide, and the rim morphology of the liquid film can change from closed to open. Increasing jet velocity and impingement angle destabilize and break up the region above the impingement point, leading to finger-like structures appearing at the rim of the liquid film. Turbulent disturbances in the liquid jet excite two-dimensional surface waves on the liquid film after impinging on the wall. The initial surface waves near the impingement point undergo spanwise evolution during downstream development, exhibiting three-dimensional characteristics. Faster jet velocities lead to stronger disturbances on the jet surface, resulting in more complex surface waves on the liquid film surface, while three-dimensional surface waves are closer to the impingement point. The formation of surface waves affects the flow and thickness distribution of the liquid film. At the wave crests, the flow velocity of the liquid film is faster. As the waves develop downstream, the velocity at wave crests will gradually decrease. A chasing phenomenon between waves can also be observed on the liquid film surface.