A multi-phase fluid method has been adopted to model the behaviour of fragmenting interfaces. The flow field is described through the solution of the Navier-Stokes equations with an approximate projection method. The interface separating the two phases is captured by a {\em level-set} function. The interface dynamics and its modelling are the main topics addressed in the present numerical study. High gradients of density, viscosity, pressure and velocity are localized at the interface. Therefore attention has to be paid to the discretization of the equations in that area. Here, an original variable coefficients ENO scheme and a redefined reinitalizaiton procedure for the Level set function led to higher accuracy. An exponential smoothing of the density and the split of the Poisson equations for the pressure terms improved the stability properties of the solver. The resulting scheme has been extensively verified and validated through canonical problems, where the method showed good capability of handling: a) high deformation of the interface with breaking and air entrainment; b) generation and evolution of vorticity and c) its interaction with the interface. Dedicated experiments have been performed for the case of a surface piercing plate in forward motion. Flow visualizations and velocity field measurements were carried out and compared with the numerical results. The globally satisfactory agreements allowed for a synergistic use of the numerical and experimental tools within a parametric analysis. The influence of the Froude number and of the plate inclination have been investigated. The former highlighted the role of the post-breaking phenomena in the definition of the different regimes of interaction between vorticity and free surface. The latter highlighted the influence of the inclination on the occurrence of breaking and on the dynamics of the vorticty released. In particular, very large positive and negative inclinations of the plate prevent energetic breaking.
Violent disturbance and fragmentation of free surfaces
2004
Abstract
A multi-phase fluid method has been adopted to model the behaviour of fragmenting interfaces. The flow field is described through the solution of the Navier-Stokes equations with an approximate projection method. The interface separating the two phases is captured by a {\em level-set} function. The interface dynamics and its modelling are the main topics addressed in the present numerical study. High gradients of density, viscosity, pressure and velocity are localized at the interface. Therefore attention has to be paid to the discretization of the equations in that area. Here, an original variable coefficients ENO scheme and a redefined reinitalizaiton procedure for the Level set function led to higher accuracy. An exponential smoothing of the density and the split of the Poisson equations for the pressure terms improved the stability properties of the solver. The resulting scheme has been extensively verified and validated through canonical problems, where the method showed good capability of handling: a) high deformation of the interface with breaking and air entrainment; b) generation and evolution of vorticity and c) its interaction with the interface. Dedicated experiments have been performed for the case of a surface piercing plate in forward motion. Flow visualizations and velocity field measurements were carried out and compared with the numerical results. The globally satisfactory agreements allowed for a synergistic use of the numerical and experimental tools within a parametric analysis. The influence of the Froude number and of the plate inclination have been investigated. The former highlighted the role of the post-breaking phenomena in the definition of the different regimes of interaction between vorticity and free surface. The latter highlighted the influence of the inclination on the occurrence of breaking and on the dynamics of the vorticty released. In particular, very large positive and negative inclinations of the plate prevent energetic breaking.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
