Numerical Simulation And Analysis Of Complex Moving Multimedium Interface

The numerical simulation of multimedium flow problem is of great difficulty in computational fluid dynamics.In addition to the complex geometrical deformation of interface,more restrictive conditions should be satisfied for numerical methods to consider the influences of material properties differences.In this work,the front tracking method is combined with the ghost fluid method to numerically simulate multimedium flow with complex moving interface,which includes compressible mediums,coexistence of compressible gas with incompressible liquid,and fluid-structure interaction with cavitation.Moreover,the effects of numerical methods on conservative errors are analyzed and dicussed for two-dimensional multimedium flow.The research work and achievements are listed as follows:(1)Perform research on the moving interface numerical method for two-dimensional compressible multimedium flow.The interface is discretised by sereval marker points and the ghost fluid method is applied to define the interface boundary conditions.A Riemann problem is constructured along the normal direction of the marker point to predict the interfacial states,with the goal of advancing the interface and obtaining the ghost fluid states directly.The comparison with earlier work in the numerical examples shows the effectiveness of procedures.Beyond that,from the perspective of conservative errors,the adaptativity of ghost fluid method is studied quantificationally with different initial conditions in the flow field.(2)Investigate the numerical method for multimedium flow based on RKDG scheme.Due to the solution plynomials and good compactness of RKDG scheme,the initial conditions to interfacial Riemann problem are obtained directly,and inaccurate ghost fluid states far from the interface are not involved in the computation.The accuracy is validated in the one-dimensional numerical examples,while the two-dimensional numerical examples show that the RKDG scheme possesses the capability of smaller conservative errors compared to the finite difference scheme.(3)Study on the numerical method for compressible gas/incompressible liquid interface.The reasons for the numerical errors in the treatment of interface are analyzed for new GFM,and a compressible/incompressible interfacial Riemann problem is constructured along the normal direction of the marker point to define the interface boundary conditions.Both mediums are solved by the DG method.Since the time step is generally not a constant in the numerical simulation of multimedium flow,a DG method with nonuniform time step is derived here for solving incompressible flow.The conservative errors of compressible gas are calculated in the numerical examples,and it demonstrates that the proposed method is more accurate and robust compared to the new GFM in earlier work.(4)Indagate the numerical method for fluid-structure interaction with cavitation.Both the fluid and structure are modeled as compressible mediums with respective equation of state.A fluid-structure Riemann problem is constructured along the normal direction of the marker point to predict the interfacial states.The solution for Riemann problem is modified when the structure is under plastic deformation,the pressure ratio of fluid and structure is not very high or the caviation occurs near the interface.Different with earlier work,the nonphysical negative interfacial pressure is modified directly from the liquid side by the isentropic one-fluid cavitation model.Extensive complex numerical examples are provided to illustrate the accuracy and effectiveness of proposed method.