Abstract
One of the methods of spraying liquid is the ultrasonic mesh method, in which the liquid is pushed out of a thin metal plate with hundreds to thousands of micropores (also called mesh) by ultrasonic vibration. The frequency of the ultrasonic vibration applied is about 100 to 300 kHz. The distance between the vibrating surface and the mesh is very small compared to the radius of the mesh. Due to the pressure distribution on the mesh surface in contact with the liquid, droplets are formed only from a limited area of the mesh. Determining the active area is important in the development of the mesh atomization equipment. As the first step of the research, we investigated the liquid squeeze flow between the ultrasonic vibrating surface and the static plate without micropores. The compressibility of the liquid becomes remarkable at high-frequency ultrasonic vibration. The pressure oscillation generated by the vibrating surface periodically varied displacement is the product of the fluid density, the sound speed, and the vibration velocity. To accommodate this situation with incompressible flow approximation, it is vital to impose a vibrating pressure boundary condition on the vibrating surface. Modeling and numerical analysis of this flow were conducted by applying a sinusoidal pressure vibration on this surface. The cases including and excluding nonlinear inertia terms and the influence of Reynolds number on this flow were investigated. It has been clarified that the pressure has extrema in the center of the plate and exhibits a parabolic distribution in the radial direction. In the absence of the nonlinear inertia terms, the radial velocity component is positively and negatively symmetric during each period. This symmetry is broken when including the non-linear inertia terms. At a higher Reynolds number, the radial velocity component maintains almost constant across the squeeze gap except for at the vicinity near the walls where boundary layers are observed.
