We present a novel approach to kinetic theory modeling enabling the simulation of a generic, real gas presented by its corresponding equation of state. The model is based on mass, momentum and energy conservation, and unlike the lattice Boltzmann models enables simulations of fluids exhibiting a liquid-vapor phase transition in both super- and subcritical states. In this new kinetic theory,an arbitrary equation of state can be introduced through rescaling the discrete particle velocities.Different benchmarks associated with real-gas thermodynamics illustrate that the proposed scheme can handle a wide range of compressible multiphase flows.
Derivation of governing equations for multiphase flow on the base of thermodynamically compatible systems theory is presented. The mixture is considered as a continuum in which the multiphase character of the flow is taken into account. The resulting governing equations of the formulated model belong to the class of hyperbolic systems of conservation laws. In order to examine the reliability of the model, the one-dimensional Riemann problem for the four phase flow is studied numerically with the use of the MUSCL-Hancock method in conjunction with the GFORCE flux.
This paper presents a new multiphase flow code, cast under an open-source GNU license. The main characteristics of the different flow models are given, then the numerical method used is briefly presented: it includes temporal flow solvers, meshing features (like AMR technics), results visualization.Two examples of flows solutions are presented: the interaction of a high-speed flow with a droplet and the second concerns the attenuation of a propagating shock wave.
A conservative Godunov-type mesh-free hydrodynamics scheme for weakly compressible multiphase flows
Technical University of Munich (TUM)（慕尼黑工业大学）；Munich Institute of Integrated Materials, Energy and Process Engineering (MEP), Technical University of Munich (TUM)（慕尼黑工业大学集成材料、能源和工艺工程研究所）
The following paper presents two simulation strategies for compressible two-phase or multicomponent flows. One is a full non-equilibrium model in which the pressure and velocity are driven towards the equilibrium at interfaces by numerical relaxation processes, the second is a four-equation model that assumes stiff mechanical and thermal equilibrium between phases or components. In both approaches, the thermodynamic behaviour of each fluid is modelled independently according to the stiffened-gas equations of state. The presented methods are used to simulate the de-pressurization of a pipe cont…
Viscous and gravitational fingering refer to flow instabilities in porous media that are triggered by adverse mobility or density ratios, respectively. These instabilities have been studied extensively in the past for 1) single-phase flow (e.g., contaminant transport in groundwater, first-contact-miscible displacement of oil by gas in hydrocarbon production), and 2) multi-phase immiscible and incompressible flow (e.g., water-alternating-gas (WAG) injection in oil reservoirs). Fingering in multiphase compositional and compressible flow has received much less attention, perhaps due to its high c…
This work describes three diffuse-interface methods for the simulation of immiscible, compressible multiphase fluid flows and elastic-plastic deformation in solids. The first method is the localized-artificial-diffusivity approach of Cook (2007), Subramaniam et al., (2018), and Adler and Lele (2019), in which artificial diffusion terms are added to the conservation equations. The second method is the gradient-form approach that is based on the quasi-conservative method of Shukla et al., (2010) and Tiwari et al., (2013), in which the diffusion and sharpening terms (together called regularizatio…
DNS of compressible multiphase flows through the Eulerian approach
Scuola Normale Superiore di Pisa（比萨高等师范学院）；Istituto Nazionale di Vulcanologia e Geofisica（意大利火山学与地球物理研究所）；Istituto Nazionale di Geofisica e Vulcanologia（意大利地球物理与火山学研究所）
A numerical procedure was developed for solving equations for compressible granular multiphase flows in which the particle volume fraction can range dynamically from very dilute to very dense. The procedure uses a low-dissipation and high-order numerical method that can describe shocks and incorporates a particulate model based on kinetic theory. The algorithm separates edges of a computational cell into gas and solid sections where gas- and granular-phase Riemann problems are solved independently. Solutions from these individual Riemann problems are combined to assemble the fully coupled conv…
A two-phase model and its application to wavefields numerical simulation are discussed in the context of modeling of compressible fluid flows in elastic porous media. The derivation of the model is based on a theory of thermodynamically compatible systems and on a model of nonlinear elastoplasticity combined with a two-phase compressible fluid flow model. The governing equations of the model include phase mass conservation laws, a total momentum conservation law, an equation for the relative velocities of the phases, an equation for mixture distortion, and a balance equation for porosity. They…
Direct numerical simulation of a compressible multiphase flow through the fast Eulerian approach
Scuola Normale Superiore di Pisa（比萨高等师范学院）；Istituto Nazionale di Vulcanologia e Geofisica（火山学与地球物理学国家研究所）；Istituto Nazionale di Geofisica e Vulcanologia（地球物理学与火山学国家研究所）
The seven-equation model is a compressible multiphase formulation that allows for phasic velocity and pressure disequilibrium. These equations are solved using a diffused interface method that models resolved multiphase flows. Novel extensions are proposed for including the effects of surface tension, viscosity, multi-species, and reactions. The allowed non-equilibrium of pressure in the seven-equation model provides numerical stability in strong shocks and allows for arbitrary and independent equations of states. A discrete equations method (DEM) models the fluxes. We show that even though st…
We propose a numerical methodology for the numerical simulation of distinct, interacting physical processes described by a combination of compressible, inert and reactive forms of the Euler equations, multiphase equations and elastoplastic equations. These systems of equations are usually solved by coupling finite element and CFD models. Here we solve them simultaneously, by recasting all the equations in the same, hyperbolic form and solving them on the same grid with the same finite-volume numerical schemes. The proposed compressible, multiphase, hydrodynamic formulation can employ a hierarc…
Multiphase, compressible and viscous flows are of crucial importance in a wide range of scientific and engineering problems. Despite the large effort paid in the last decades to develop accurate and efficient numerical techniques to address this kind of problems, current models need to be further improved to address realistic applications. In this context, we propose a numerical approach to the simulation of multiphase, viscous flows where a compressible and an incompressible phase interact in the low-Mach number regime. In this frame, acoustics is neglected but large density variations of the…
A conservative coupling method of sharp-interface and multi-species model for compressible reacting gas-liquid flows with phase change
School of Aeronautics, Northwestern Polytechnical University（西北工业大学航空学院）；National Key Laboratory of Aircraft Configuration Design（飞机设计国家重点实验室）；Institute of Extreme Mechanics, Northwestern Polytechnical University（西北工业大学极端力学研究所）
The interactions between rocket exhaust plumes and the surface of extraterrestrial bodies during spacecraft landings involve complex multiphase flow dynamics that pose significant risk to space exploration missions. The two-phase flow is characterized by high Reynolds and Mach number conditions with particle concentrations ranging from dilute to close-packing. Low atmospheric pressure and gravity typically encountered in landing environments combined with reduced optical access by the granular material pose significant challenges for experimental investigations. Consequently, numerical modelin…
Speed of sound is a key parameter for the compressibility effects in multiphase flow. We present a new approach to do direct numerical simulations on the speed of sound in compressible two-phase flow, based on the stratified multiphase flow model (Chang & Liou, JCP 2007). In this method, each face is divided into gas-gas, gas-liquid, and liquid-liquid parts via reconstruction of volume fraction, and the corresponding fluxes are calculated by Riemann solvers. Viscosity and heat transfer models are included. The effects of frequency (below the natural frequency of bubbles), volume fraction, visc…
Within the framework of diffuse interface methods, we derive a pressure-based Baer-Nunziato type model well-suited to weakly compressible multiphase flows. The model can easily deal with different equation of states and it includes relaxation terms characterized by user-defined finite parameters, which drive the pressure and velocity of each phase toward the equilibrium. There is no clear notion of speed of sound, and thus, most of the classical low Mach approximation cannot easily be cast in this context. The proposed solution strategy consists of two operators: a semi-implicit finite-volume …
The goal of this report is to present the final project conducted in order to fulfill the requirements of the M.Sc. degree at the Department of Mechanical Engineering, Ben-Gurion University (BGU) of the Negev. The project comprises theoretical research investigating natural convection compressible flow with high temperature differences and with complex geometries. The research motivation comes from long-term research investigating and simulating the steady state and transient multiphase flow regimes existing in the reactor core, that was established by the Soreq Nuclear Center. The main object…
Fluctuating hydrodynamics provides a model for fluids at mesoscopic scales where thermal fluctuations can have a significant impact on the behavior of the system. Here we investigate a model for fluctuating hydrodynamics of a single component, multiphase flow in the neighborhood of the critical point. The system is modeled using a compressible flow formulation with a van der Waals equation of state, incorporating a Korteweg stress term to treat interfacial tension. We present a numerical algorithm for modeling this system based on an extension of algorithms developed for fluctuating hydrodynam…
Although there have been extensive experimental and computational investigations in characterizing cavitation phenomenon in both diesel and gasoline direct injectors, much is still unknown about the mechanisms driving cavitation-induced erosion, and how this complicated fluid-structure interaction should be modeled. To explore current modeling capabilities, a numerical investigation was conducted within the CONVERGE modeling framework to assess proposed cavitation erosion metrics in the literature, and their link to the predicted cavitation cloud collapse mechanism. The multiphase flow within …
In this paper we study the motion of a fluid with several dispersed particles whose concentration is very small (smaller than $10^{-3}$), with possible applications to problems coming from geophysics, meteorology, and oceanography. We consider a very dilute suspension of heavy particles in a quasi-incompressible fluid (low Mach number). In our case the Stokes number is small and --as pointed out in the theory of multiphase turbulence-- we can use an Eulerian model instead of a Lagrangian one. The assumption of low concentration allows us to disregard particle--particle interactions, but we tak…
