Multiphase Mixture Flow Research Articles

A Computational Fluid Dynamics Study on Shearing Mechanisms in Thermal Elastohydrodynamic Line Contacts

A computational fluid dynamics (CFD) model of the thermal elastohydrodynamically lubricated (EHL) line contact problem has been developed for the purpose of exploring the physical processes that occur inside a thin EHL film subjected to shearing motion. The Navier–Stokes equations are solved by using the finite volume method (FVM) in a commercial CFD software, ANSYS Fluent. A set of user-defined functions (UDF) are used for computing viscosity, density, heat source, temperature of moving surfaces and elastic deformation of the top roller according to well-established equations commonly used in the EHL theory. The cavitation problem is solved by taking into account multiphase mixture flow. The model combinations of Houpert and Ree–Eyring and of Tait and Carreau were used for modeling the non-Newtonian behavior of Squalane and the results were compared. Both rheological models suggest the existence of shear-band and plug-flow at high fluid pressure. Due to the differences in viscosity at GPa-level pressure, the chosen model has substantial influence on the computed shear stress and temperature distributions in the high-pressure region. This shows the importance of using correct rheology information in the whole range of pressure, temperature, and shear strain rate.

Numerical investigation of the rake angle effect on the hydrodynamic performance of propeller in a uniform and nonuniform flow

Marine propeller always operates in the wake of a vehicle (ship, torpedo, submarine) but (due to the high computational cost of simulating vehicle and propeller simultaneously) to investigate the propeller geometric parameters, simulations are usually performed in open-water conditions. In this article, using the computational fluid dynamics method with the control volume approach, the effect of the rake angle on the propeller performance and formation of cavitation in the uniform flow (open water) and the nonuniform flow (wake flow) was investigated. In the nonuniform condition, the array of plates was used to simulate wake at upstream propeller. For uniform flow, steady solution scheme was adopted and for nonuniform flow unsteady solution scheme was adopted, and a moving mesh zone was generated around the propeller. To simulate cavitation a multiphase mixture flow, the Reynolds-averaged Navier–Stokes method was used and modeled by Schnerr Sauer's cavitation model. First, the E779a propeller model for numerical validation in the uniform flow and nonuniform flow was investigated. Numerical results were compared with the experimental result, and there was a good agreement between volume of the cavity, thrust, and torque coefficients. To study the effect of rake angle on the performance of B-series propellers, four models with different rake angles were modeled, and simulation was investigated behind the wake. The results of thrust, torque coefficients, and cavitation volume according to the flow parameters and cavitation number were presented as graphs. The results reveals that in the uniform flow, the rake angle has no significant effect on the propeller performance, but behind the wake flow, increase of rake causes to reduce the force applied to the propeller blades, cavitation volume, and pressure fluctuations on the propeller.

Numerical investigation of a modified family of centered schemes applied to multiphase equations with nonconservative sources

Systems of hyperbolic partial differential equations are frequently used to model the flow of multiphase mixtures. These equations often contain sources, referred to as nozzling terms, that cannot be posed in divergence form, and have proven to be particularly challenging in the development of finite-volume methods. Upwind schemes have recently shown promise in properly resolving the steady wave solution of the associated multiphase Riemann problem. However, these methods require a full characteristic decomposition of the system eigenstructure, which may be either unavailable or computationally expensive. Central schemes, such as the Kurganov–Tadmor (KT) family of methods, require minimal characteristic information, which makes them easily applicable to systems with an arbitrary number of phases. However, the proper implementation of nozzling terms in these schemes has been mathematically ambiguous. The primary objectives of this work are twofold: first, an extension of the KT family of schemes is proposed that formally accounts for the nonconservative nozzling sources. This modification results in a semidiscrete form that retains the simplicity of its predecessor and introduces little additional computational expense. Second, this modified method is applied to multiple, but equivalent, forms of the multiphase equations to perform a numerical study by solving several one-dimensional test problems. Both ideal and Mie–Grüneisen equations of state are used, with the results compared to an analytical solution. This study demonstrates that the magnitudes of the resulting numerical errors are sensitive to the form of the equations considered, and suggests an optimal form to minimize these errors. Finally, a separate modification of the wave propagation speeds used in the KT family is also suggested that can reduce the extent of numerical diffusion in multiphase flows.

Numerical Simulation and Influencing Factors Analysis of the Leakage and infiltration diffusion for Fuel Underground Storage Tank

Mass and heat transfer processes of three fuels commonly used (Liquefied Petroleum Gas (LPG), gasoline, diesel oil) flow dispersing in underground environment for the leak at different zones of underground storage tank (UST) were studied. On the basis of the mass and heat transfer process analysis and employing the three-dimensional multiphase mixture flow model, the migration processes of LPG, gasoline, diesel oil in tank pond for UST leak were simulated. The velocity, density, concentration, pressure, temperature fields can be obtained. From the simulation results, the detailed analysis were performed to investigate the characteristics of the three fuels infiltration flow processes and the effects of various influencing factors on infiltration flow such as storage pressure, fuel composition, leak position of tank, position of outlet, gravity, viscous force, etc.

Numerical Simulation of High Velocity Waterjet Characteristics and Impact Pressure

This paper presents a numerical simulation approach to analyze high velocity waterjet characteristics and impact pressure. For the complexity of waterjet formation in air, multiphase mixture flow model is used, and the simulation is performed in FLUNET software. The simulation includes the hydrodynamic characteristics and pressure distribution of high velocity waterjet in air. The decay of pressure at different distance along centerline under different pump pressure is analyzed and the length of the initial region of waterjet is determined. In addition, the impact pressure of waterjet at different stand-off distance is also simulated, and the impact pressure distribution and its changing tendency with the stand-off distance are obtained. This paper provides theoretical parameters for waterjet incremental sheet metal forming.

Towards numerical prediction of unsteady sheet cavitation on hydrofoils

The paper presents a study of using a modified k-ω model to predict the unsteady cavitating flows around 2D and 3D hydrofoils in the framework of multi-phase mixture flow RANS approach. The cavitation is modeled by Schnerr-Sauer's cavitation model. A 2D NACA0015 foil at cavitation number σ=1.0 (unsteady with cloud shedding) is studied first, followed by the Delft twisted 3D foil. It is found that the present RANS method is able to predict the essential features like re-entrant jets, the periodic shearing and shedding of cloud cavities. Two distinct shedding dynamics are noted for the 2D foil: (a) Shedding of medium to large scale structures (at low frequency); (b) Shedding of a series of secondary vortex cavities (at high frequency). For the 3D twisted foil, the collaborated effect of re-entrant jets from the curved closure line to break up a primary cavity, as well as the formation, roll-up and transport of cavitation vortices that are observed in the experiment are truly reproduced in the simulation. The method is found to have a tendency to under-predict the lift coefficients.

An investigation of interface-sharpening schemes for multi-phase mixture flows

This work evaluates several approaches for sharp phase interface-capturing in computations of multi-phase mixture flows. Attention is focused on algebraic interface-capturing strategies that fit directly within a finite-volume MUSCL-type framework, in which dimension-by-dimension reconstruction of interface states based on extrapolated fluid properties is the norm. In this scope, linear, sine-wave, and tangent hyperbola volume-fraction reconstructions are examined for a range of problems, including advection of a volume-fraction discontinuity, the Rayleigh–Taylor instability, a dam-break problem, an axisymmetric jet instability, the Rayleigh instability, and flow within an aerated-liquid injector. An implicit dual-time stepping approach, applied directly to a preconditioned form of the governing equations, is used for time-advancement. The results show that the sharpening strategies are successful in providing two-to-three-cell capturing of volume-fraction discontinuities.

Modeling of multicomponent multiphase mixture flows on the basis of the density-functional method

Modeling of multicomponent multiphase mixture flows on the basis of the density-functional method

Modeling of multicomponent multiphase mixture flows on the basis of the density-functional method

Examples of numerical calculations of isothermal flows of two-phase two-component mixtures based on the density-functional method are presented. Using this method, the following problems are calculated in the two-dimensional formulation: drop impact on a liquid layer, drop rupture in a Couette flowfield, wetting-angle formation for a drop on a solid surface, development of Rayleigh-Taylor and Kelvin-Helmholtz instability on a gas-liquid interface.

A Model for Multiphase Flows through Poroelastic Media

A continuum model for multiphase fluid mixture flows through poroelastic media is presented. The basic conservation laws developed via a volume averaging technique are considered. Effects of phasic equilibrated forces are included in the model. Based on the thermodynamics of the multiphase mixture flows, appropriate constitutive equations are formulated. The entropy inequality is exploited, and the method of Lagrangian multiplier is used along with the phasic conservation laws to derive the constitutive equations for the phasic stress tensors, equilibrated stress vectors, and the interactions terms. The special cases of wave propagation in poroelastic media saturated with multiphase fluids, and multiphase flows through porous media, are studied. It is shown that the present theory leads to the extended Darcy’s law and contains, as a special case, Biot’s theory of saturated poroelastic media.

Computation of Multiphase Mixture Flows with Compressibility Effects

A time-marching computational fluid dynamics method is developed and applied to the computation of multiphase mixture flows. The model accounts for finite acoustic speeds in the constituent phases, which typically lead to transonic/supersonic flow and associated compressibility phenomena such as shock formation in the mixture region. Preconditioning or artificial compressibility methods are devised using perturbation theory to insure that the method retains efficiency and accuracy in both the incompressible and compressible flow regimes. The resulting algorithm is incorporated within an existing multiphase code, and several representative applications are used to demonstrate the capabilities of the method. In particular, our results suggest that the present compressible formulation provides an improved description of cavitation dynamics compared with previous incompressible computations.

Critical and Subcritical Flow of Multiphase Mixtures Through Chokes

SummaryEquations that describe isentropic (adiabatic with no friction loss) flow of multiphase mixtures through chokes can be deduced from the general energy equation. These flow equations are valid for both critical and subcritical flow. Equations, physical property correlations for oil/water/natural gas systems, and a computer method that will handle both flow regimes are described. The procedure will determine whether flow will be in the critical or subcritical regime. The analysis method has been tested by comparing measured and calculated flow rates of 1, 432 sets of literature data comprising both critical and subcritical air/water, air/kerosene, natural gas, natural gas/oil, natural gas/water, and water flows. An average discharge coefficient of 0.826 gave a negligible average error with a 15.4% standard deviation.