Numerical Study On The Interaction Between Solid Obiects And Gas-liquid Interface

The interaction between solid object and gas-liquid interface widely exists in nature and industrial applications,involving complicated flow phenomena such as fluidstructure interaction,moving contact line and capillary wave evolution.The research on the mechanism of these flows has important scientific significance and industrial application prospect.In this thesis,we develop a fluid-structure interaction multiphase flow method upon an adaptive mesh open-source platform,and invetigate three typical interface flow problems:maximal spreading of droplets impacting the no-slip wall,water-exit of particles through a gas-liquid interface and impact dynamics of a compound droplet with a solid particle onto a wall.The summary of the research is given below:(1)The maximum spreading of droplets impacting no-slip walls with different wettability is studied,and a universal model is proposed to predict the maximal spreading of droplets at moderate Weber number.We find that the wettability plays an important role in the maximal spreading,and the ratio of transformed surface energy to the initial kinetic energy of the drop at maximal spreading obeys the scaling law of η～We-1/2 at high Reynolds number.Combined with the energy conversion analysis,the maximum spreading scaling law βmax～We1/4(1-cosθ)-1/2 is obtained at high Reynolds number.In addition,a new impact parameter is defined to make all the maximal spreading data collapse onto a single curve.A universal model for maximal spreading is obtained by smooth crossover between the viscous regime and viscous-capillary regime through Pade approximation.The model can accurately predict the maximal spreading ratio of the impacting droplet in a wide range of Reynolds number and Weber number.(2)The dynamic process of millimetric water-exit particles passing through the gasliquid interface is studied.By changing the Weber number and Bond number of the particle,three different regimes are found:break,bouncing-off and penetration.The critical conditions for the transformation between different regimes are predicted theoretically,and the critical features between bouncing-off and penetration are studied based on energy conversion analysis and Rayleigh-Plateau instability theory.The critical condition between bouncing-off and penetration is obtained by comparing the pinch-off time of liquid bridge with the time when particles fall back to the undisturbed gas-liquid interface.By analyzing the thickness of the liquid film at the top of the particle,the critical condition between break and bouncing-off is given.The theoretical predictions are in good agreement with the numerical results.(3)The spreading and retraction process of compound droplets wrapped with particles after impacting on the solid wall is studied.It is found that due to the block of the particle,the actual fluid volume involved in spreading is only(1-α)2 times of the total volume of compound droplets,where α is the volume ratio of the particle.The scaling law of the evolution of the spreading radius at early time is derived through the conservation of the mass flow.Then the retraction dynamics of droplets are analyzed,and the scaling laws for retraction rate are obtained for the cases dominated by inertia and surface tension and the cases dominated by viscosity and surface tension.It is found that the maximal spreading ratio of compound droplets is(1-α)times that of pure droplets under the same impact parameters,and a universal model of maximal spreading of compound droplets is obtained,which is in good agreement with the numerical simulation results.