Numerical simulation for fluid flow over an attached rigid body with a deformable ring bubble is analyzed based on the velocity potential theory together with the boundary element method （BEM）. The analysis is focused on the axisymmetric case. The bubble surface is treated as a well defined air-liquid interface and is tracked by a mixed Eulerian-Lagrangian method. The points of intersection between the bubble and body are treated, specially in the numerical procedure. The auxiliary function method is adopted to calculate the pressure on the body surface and in the flow field. The convergence study is undertaken to assess the developed numerical method and the computation code. Some case studies are undertaken in which the interactions between the bubble/body and the incoming flow field are simulated. The effects of various physical parameters on the interactions are investigated.
To solve the problems concerning water entry of a structure, the RANS equations and volume of fluid （VOF） method are used. Combining the user-defined function （UDF） procedure with dynamic grids, the water impact on a structure in free fall is simulated, and the velocity, displacement and the pressure distribution on the structure are investigated. The results of the numerical simulation were compared with the experimental data, and solidly consistent results have been achieved, which validates the numerical model. Therefore, this method can be used to study the water impact problems of a structure.
This paper presents a review of the work on fluid/structure impact based on inviscid and imcompressible liquid and irrotational flow. The focus is on the velocity potential theory together with boundary element method （BEM）. Fully nonlinear boundary conditions are imposed on the unknown free surface and the wetted surface of the moving body. The review includes （1） vertical and oblique water entry of a body at constant or a prescribed varying speed, as well as free fall motion, （2） liquid droplets or column impact as well as wave impact on a body, （3） similarity solution of an expanding body. It covers two dimensional （2D）, axisymmetric and three dimensional （3D） cases. Key techniques used in the numerical simulation are outlined, including mesh generation on the multivalued free surface, the stretched coordinate system for expanding domain, the auxiliary function method for decoupling the mutual dependence of the pressure and the body motion, and treatment for the jet or the thin liquid film developed during impact.
Simulations of bubble entrainment into a stationary Gaussian vortex are performed by using the combined particle tracking method(PTM)and boundary element method(BEM).Before the bubble is captured by the vortex core,oscillation and migration of the quasi-spherical nucleus are solved by using improved RP equation and the momentum theorem in the Lagrangian reference frame simultaneously,and the trajectory of the nucleus presents a kind of reduced helix shape.After captured by the vortex core,the bubble grows immediately and moves and deforms along the vortex core axis.The non-spherical evolution and deformation of the bubble is simulated by adopting a mixed Eulerian-Lagrangian method.The output of quasi-spherical stage is taken as the input of non-spherical stage,and all the behaviors of the entrained bubble can be simulated such as inception,motion,deformation and split.Numerical results agree well with published experimental data.On this basis,the influences of various factors such as viscosity,surface tension,buoyancy are studied systemically.Hopefully the results from this paper would provide some insight into the control on vortex bubble entrainment.
