An ISPH scheme for numerical simulation of multiphase flows with complex interfaces and high density ratios

This paper presents a numerical model that intends to simulate efficiently the surface instability that arise in multiphase flows, typically liquid-gas, both for laminar or turbulent regimes. The model is developed on the in-house computing platform TermoFluids, and operates the finite-volume, direct numerical simulation (DNS) of multiphase flows by means of a conservative level-set method for the interface-capturing. The mesh size is optimized by means of an adaptive mesh refinement (AMR) strategy, that allows the dynamic re-concentration of the mesh in the vicinity of the interfaces between fluids, in order to correctly represent the diverse structures (as ligaments and droplets) that may rise from unstable phenomena. In addition, special attention is given to the discretization of the various terms of the momentum equations, to ensure stability of the flow and correct representation of turbulent vortices. As shown, the method is capable of truthfully simulate the interface phenomena as the Kelvin-Helmholtz instability and the Plateau-Rayleigh instability, both in the case of 2-D and 3-D configurations. Therefore it is suitable for the simulation of complex phenomena such as simulation of air-blast atomization, with several important application in the field of automotive and aerospace engines. A prove is given by our preliminary study of the 3-D coaxial liquid-gas jet.

A new massively parallel scheme is developed to simulate free-surface flows with the meshless method incompressible smoothed particle hydrodynamics (ISPH) for simulations involving more than 100 million particles. As a pressure-projection method, ISPH requires the solution of a sparse matrix for the pressure Poisson equation (PPE) which is non trivial for large problems where the particles are moving with continuously evolving sparsity. The new scheme uses a Hilbert space filling curve with a cell-linked list to map the entire domain so that domain decomposition and load balancing can be achieved easily to take advantage of geometric locality in order to reduce latency in memory cache access. The computational domain can be subdivided into more than 12,000 partitions using the message passing interface (MPI) for communication between partitions. Load balancing is achieved using the open-source Zoltan library using a new particle weighting system. To solve the PPE for large problems using tens of thousands of partitions, the open-source PETSc library is used which requires the HYPRE BoomerAMG preconditioner to ensure rapid convergence for ISPH. The performance of the code is benchmarked on the U.K. National Supercomputer ARCHER. The results show that domain decomposition with a space filling curve can efficiently treat irregularly distributed particles creating a well-balanced scheme demonstrating that the approach is well matched to the highly irregular subdomains and non-uniform distribution of ISPH free-surface simulations. The benchmark results show that massively parallel ISPH code can achieve over 90% efficiency for the solution of the PPE, but the efficiency of computing matrix coefficients decreases when using more than 12000 partitions giving overall efficiencies in excess of 43% up to 6144 MPI partitions, highlighting future improvements required. The work demonstrates that the Zoltan and PETSc libraries can be effectively combined with ISPH to offer the capability of developing a massively parallel ISPH toolkit.

A new two-phase incompressible-compressible Smoothed Particle Hydrodynamics (SPH) method has been developed where the interface is discontinuous in density. This is applied to water-air problems with a large density difference. The incompressible phase requires surface pressure from the compressible phase and the compressible phase requires surface velocity from the incompressible phase. Compressible SPH is used for the air phase (with the isothermal stiffened ideal gas equation of state for low Mach numbers) and divergence-free (projection based) incompressible SPH is used for the water phase, with the addition of Fickian shifting to produce sufficiently homogeneous particle distributions to enable stable, accurate, converged solutions without noise in the pressure field. Shifting is a purely numerical particle regularisation device. The interface remains a true material discontinuity at a high density ratio with continuous pressure and velocity at the interface. This approach with the physics of compressibility and incompressibility represented is novel within SPH and is validated against semi-analytical results for a two-phase elongating and oscillating water drop, analytical results for low amplitude inviscid standing waves, the Kelvin-Helmholtz instability, and a dam break problem with high interface distortion and impact on a vertical wall where experimental and other numerical results are available.

A coupled distributed Lagrange multiplier (DLM) and discrete element method (DEM) approach to simulate particulate flow with collisions

In this paper, the in-house code based on the smoothed particle hydrodynamics is proposed to simulate a fluid-solid interaction (FSI) problem. This method is a Lagrangian, mesh-free method and it has a high ability to capture the free surface in two phase flows and also the interface in FSI problems. To compare ofweakly compressible SPH (WCSPH) and incompressible SPH (ISPH) schemes, fluid flow under a hypo-elastic gate is simulated in solid and fluid domains with both methods. At first fluid domain is simulated with ISPH method and solid domain is solved with WCSPH scheme. Another simulation is done with both fluid and solid parts solved with WCSPH method. The results of both methods are in a good agreement with each other and also with other researcher’s results. So it is concluded that it is easier to model the fluid flow with ISPH scheme and the solid part with WCSPH in coupling fluid-solid interaction problems with a good accuracy.

A partitioned continuous surface stress model for multiphase smoothed particle hydrodynamics

Computation of compressible flows with high density ratio and pressure ratio

An interface capturing scheme for modeling atomization in compressible flows

Development of singular value decomposition based solution scheme for a numerical simulation of multiphase flow

Elastocapillarity modeling of multiphase flow-induced solid deformation using volume of fluid method

The computation of multiphase flows presenting high density ratios, where the fluids involved are considered immiscible, are of great importance for fundamental physics and industrial applications; such as the study of liquid-gas interfaces, wave motion, simulation of bubbly flows and atomization, injection in diesel engines, chemical processes and others. This work presents and analyzes a collocated and staggered finite-volume mesh discretizations suitable for three-dimensional unstructured meshes, which are able to simulate immiscible multiphase flows with high density ratios. More over, these mesh schemes numerically conserve mass and momentum while minimize errors in the conservation of kinetic energy.

In this paper, electrohydrodynamics (EHD) deformation of a droplet in a highly confined domain is studied by using the incompressible smoothed particle hydrodynamics method. Simulations are performed for six different systems of a droplet and ambient fluid corresponding to different electrical properties. The effects of confinement ratios, from 0 to 0.95, on the droplet deformation are discussed thoroughly. It is shown that the deformation is highly dependent on the ratios of electrical permittivity, electrical conductivity, and confinement ratio. To demonstrate the droplet behavior, electric force components on the droplet interface are calculated and discussed in detail. It is shown that the interaction of these forces plays a major role in the droplet deformation. Furthermore, it is illustrated that the pressure force becomes significant at high confinement ratios and affects the droplet behavior in addition to the electric forces. Different values of unbounded deformation are selected for the EHD simulation. The effect of unbounded deformation on the droplet behavior is also discussed, and it is found that the unbounded deformation influence is important in some of the systems and confinement ratios.

A lattice Boltzmann model for multi-component two-phase gas-liquid flow with realistic fluid properties

A phase-field lattice Boltzmann model for simulating multiphase flows in porous media: Application and comparison to experiments of CO2 sequestration at pore scale

In this paper, we present numerical studies on multiphase flows related to food and pharmaceutical applications, focusing on the Discrete Element Method (DEM) and solid–fluid interaction simulations using the DEM. Specifically, we describe numerical models of the DEM coupled with the Volume-of-Fluid method and the DEM coupled with the Lattice Boltzmann Method, along with their application examples. In addition, we present the studies regarding the Reduced-Order Model based on Proper Orthogonal Decomposition.