A front-tracking/ghost-fluid method is introduced for simulations of fluid interfaces in compressible flows. The new method captures fluid interfaces using explicit front-tracking and defines ...interface conditions with the ghost-fluid method. Several examples of multiphase flow simulations, including a shock–bubble interaction, the Richtmyer–Meshkov instability, the Rayleigh–Taylor instability, the collapse of an air bubble in water and the breakup of a water drop in air, using the Euler or the Navier–Stokes equations, are performed in order to demonstrate the accuracy and capability of the new method. The computational results are compared with experiments and earlier computational studies. The results show that the new method can simulate interface dynamics accurately, including the effect of surface tension. Results for compressible gas–water systems show that the new method can be used for simulations of fluid interface with large density differences.
•A three-phase numerical model for air–steam mixture condensation flows is presented.•A fully compressible multiphase homogeneous mixture flow model is adopted.•The numerical results are in good ...agreement with experimental data.•Condensate water film layer thickness of almost 4.0 mm is observed at the outlet tube.•The effects of air mass fraction on condensation rate are investigated.
In this study, a fully compressible three-phase numerical model for steam condensation flow in the presence of air is presented. The model solves the Reynolds-averaged Navier–Stokes equation coupled with two interface advection equations. The Lee condensation model was applied to simulate the mass and energy transfer processes via interfaces. Several test cases were simulated for the air–steam mixture condensation flow in a vertical tube with different air mass fractions to verify the numerical model. The validity was demonstrated through comparisons of the centerline temperatures along the tube and experimental data; the results were in good agreement with experimental data. A detailed radial profile of the temperature, species mass fraction, and velocity was analyzed. A developing thin condensate water film along the tube and the thickest film layer at the outlet tube wall of approximately 4.0 mm were observed. Air accumulation at the steam–water interface was also represented. In addition, the effects of air mass fraction on the characteristics of the condensation rate were investigated.
•Cavity pulsation can substantially depend on this content because of compressibility of gas-liquid mixtures within the cavities.•Compressibility is predetermined by the local sound speed that ...sharply depends on void fraction and pressure within the cavities.•This paper provides numerical analysis of the influence of cavity content on pulsations and compares the results with experimental data for a specially designed hydrofoil.
Assumptions on the cavity content have an insignificant influence on predictions of time-average characteristics of sheet cavitation. However, cavity pulsation can substantially depend on this content because of compressibility of gas-liquid mixtures within the cavities. Compressibility is predetermined by the local sound speed that sharply depends on void fraction and pressure within the cavities. This speed can be indeed very small, whereas used in many CFD solvers definitions of the mixture density as a linear combination of component densities can lead to enormous overestimation of this speed and, as a result, to underestimation of pulsations of cavity volume and of body lift and drag. This paper provides numerical analysis of the influence of cavity content on pulsations and compares the results with experimental data for a specially designed hydrofoil.
Here we extend the Toro–Vázquez flux vector splitting approach (TV), originally proposed for the ideal 1D Euler equations in 1, to the Baer–Nunziato equations of compressible two-phase flow. ...Following the TV approach we identify corresponding advection and pressure operators. We perform a rigorous analysis of the associated non-conservative pressure system and derive its complete characteristic structure. The choice of the advection numerical flux is obvious. For the pressure system, several schemes are presented. The complete schemes are then implemented in the setting of finite volume and path-conservative methods and are systematically assessed in terms of accuracy and efficiency, through a carefully selected suite of test problems. The presented schemes constitute a building block for the construction of high-order numerical methods for solving the Baer–Nunziato equations. Here, as an illustrative example of such possibility, we present the construction of a second-order scheme.
We first construct an approximate Riemann solver of the HLLC-type for the Baer–Nunziato equations of compressible two-phase flow for the “subsonic” wave configuration. The solver is fully nonlinear. ...It is also complete, that is, it contains all the characteristic fields present in the exact solution of the Riemann problem. In particular, stationary contact waves are resolved exactly. We then implement and test a new upwind variant of the path-conservative approach; such schemes are suitable for solving numerically nonconservative systems. Finally, we use locally the new HLLC solver for the Baer–Nunziato equations in the framework of finite volume, discontinuous Galerkin finite element and path-conservative schemes. We systematically assess the solver on a series of carefully chosen test problems.
•The numerical simulation method of underwater implosion of spherical ceramic pressure hulls in 11,000 m depth based on compressible multiphase flow and adaptive mesh refinement is established.•The ...characteristic of shock wave generated by underwater implosion in 11,000 m depth spherical ceramic pressure hulls are analyzed.•The chain-reaction implosion is simulated, and the superposition effect between two spheres is found.•The research results of implosion are of great significance to the development of pressure hulls of deep-sea underwater vehicle.
Pressure hulls play an important role in deep-sea underwater vehicles. However, in the ultra-high pressure environment, a highly destructive phenomenon could occur to them which is called implosion. To study the characteristics of the flow field of the underwater implosion of hollow ceramic pressure hulls, the compressible multiphase flow theory, direct numerical simulation, and adaptive mesh refinement are used to numerically simulate the underwater implosion of a single ceramic pressure hull and multiple linearly arranged ceramic pressure hulls. Firstly, the feasibility of the numerical simulation method is verified. Then, the results of the flow field of the underwater implosion of hollow ceramic pressure hulls in 11000 m depth is analyzed. There are the compression-rebound processes of the internal air cavity in the implosion. In the rebound stage, a shock wave that is several times the ambient pressure is generated outside the pressure hull, and the propagation speed is close to the speed of sound. The pressure peak of the shock wave has a negative exponential power function relationship with the distance to the center of the sphere. Finally, it is found that the obvious superimposed effect between spheres exists in the chain-reaction implosion which enhances the implosion shock wave.
•An efficient parallel GPU-CPU two-phase solver is presented.•Performances and scalability are illustrated on a heterogenous supercomputer.•Several shock-induced bubble collapses near a wall are ...investigated.•Results underline the importance of 3D simulations to predict wall damages.
SCB is an efficient fluid solver developed for computing two-phase compressible flows involving strong shocks and expansion waves. It solves a four-equation diffuse-interface model, which is derived from the five-equation model proposed by Kapila et al. The governing equations are discretized by a finite volume method with explicit time stepping. SCB uses a fully parallel environment via Message Passing Interfaces (MPI). With the fast growing number of heterogeneous computing platforms including disparate hardware architectures, it becomes nowadays necessary to develop hybrid parallelization strategies with a special care to portability. In this context, we present an heterogeneous computing framework based on MPI library and OpenACC. The choice of OpenACC is discussed. Performances, scalability and adaptability are illustrated through a series of tests on an heterogeneous architecture. Validations are proposed on various bubble collapses, in free-field or near a rigid wall. Comparisons are done with existing results and analytical solutions. Furthermore a stiff shock-induced bubble collapse demonstrates the capabilities and the high potential of the code.
A modified interfacial Riemann problem accounting for phase change and surface tension was developed to couple a reacting gas to a vaporizing compressible liquid. Results from the proposed numerical ...method compare well with empirically measured separation locations over spheres, established heat-transfer correlations, and droplet deformation criterion. The numerical algorithms developed in this work are robust and applicable to a wide variety of highly transient compressible chemically reacting flows involving phase change. Computed example problems of shock wave and droplet interactions compare well with empirical measurements and show counterintuitive vaporization trends that are explainable from basic physical arguments. To the authors’ knowledge, this paper represents the first time in the open literature that a compressible reacting gas-dynamic flow has been directly coupled to a compressible cavitating liquid with vaporization using multi-fluid modeling techniques.
A numerical solver coupling the Runge-Kutta discontinuous Galerkin method to the finite element method is proposed to solve the two-dimensional (2D) or axisymmetric response of deformable sandwich ...structures with metallic foam cores subjected to underwater explosion, in which the interactions of the gas bubble, the shock wave, the sandwich structure and cavitation are taken into account. The coupling method combines the advantages of the ghost fluid method (GFM) and the modified ghost fluid method (MGFM), where the Lagrangian interface velocity is directly set as the solution of the Riemann problem and the interface pressure and the fluid density are obtained by solving the Riemann problem (with the pre-known interface velocity). The obtained interface pressure then serves as the boundary condition to the Lagrangian domain. For the Eulerian domain, the remaining procedure is similar to the MGFM. The method proposed in this paper is material independent in simulating the fluid-structure interaction which is its major advantage compared with the original MGFM. The method is successfully validated by using analytical, numerical, and experimental results.
•We propose a numerical solver coupling RKDG to FEM on a basis of MGFM.•The coupling method is structural material independent.•We validate the method by analytical, experimental and reference numerical results.•The response of a sandwich structure subjected to underwater explosion is solved.
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