Simulating collisions of droplets with walls and films using a level set method.

摘要

A coupled level set and Marker and Cell is developed for computing axisymmetric, incompressible, and immiscible two-phase flows. Instead of using marker particles to track the free surface, the level set function is employed to "capture" the complex interfacial structure. An iterative process is devised in order to maintain the level set function as the signed distance from the interface.; As a base line case, the two-phase fluid code is implemented for simulating zero gravity capillary oscillations of liquid droplet in order to validate its capability to handle surface tension effects. Initially deformed shapes of the second spherical harmonics are to oscillate and the simulation results are compared with linearized analytic solutions as well as other numerical calculations. A viscous damping towards an equilibrium sphere and capillary oscillation-period variations are investigated. Axisymmetric steady rising bubbles in an unbounded quiescent viscous liquid are simulated for a validation of code's ability in buoyancy driven deformations and stable breakup processes. The simulation results show a consistency with other numerical results for a high Weber number cases. It should be pointed out that no additional treatment is necessary to handle bubble breakups.; An impact of a liquid droplet onto solid surface and/or shallow liquid layer has been simulated and compared with corresponding experimental data. Case studies on the radial extension versus variable Weber numbers show good agreements with experimental observation. Drop collisions onto shallow liquid layer are chosen for splash simulations. The effects of layer thickness are studied by analyzing radial extension and elevation of the splash rim. Drop impingement on deep pool is also examined on purpose to simulate a crater and a central jet.; It is found that there exists a criterion to distinguish between the splashing and the deposition events in terms of a single impact parameter. A simple dimensional analysis on the energy/mass conservation during the impact and the deformation process is performed and discussed with a comparison of experimental and other numerical results.