scholarly journals Determination of Phase-Eigenvalues by Rational Factorization and Enhanced Simulation of Two-Phase Mass Flow

2019 ◽  
Vol 2 (2) ◽  
pp. 61-77
Author(s):  
Puskar R. Pokhrel ◽  
Bhadra Man Tuladhar
Keyword(s):  
Fluid Dynamics ◽  
Debris Flows ◽  
Lateral Pressure ◽  
Solid Phase ◽  
Fluid Phase ◽  
Factorization Method ◽  
Phase Interaction ◽  
Two Phase ◽  
Simulation Results

In this paper, we present simple and exact eigenvalues for both the solid- and fluid-phases of the real two-phase general model developed by Pudasaini (2012); we call these phase-eigenvalues, the solid- phase-eigenvalues and the fluid-phase-eigenvalues. Results are compared by applying the derived phase- eigenvalues that incorporate the phase-interactions in the two-phase debris movements against the simple and classical solid and fluid eigenvalues without any phase interaction. We have constructed several different set of eigenvalues including the coupled phase eigenvalues by using rational factorization method. At first, we consider for general debris height; factorizing the solid and fluid lateral pressure contributions by considering the negligible pressure gradient; negligible solid lateral pressure; negligible fluid lateral pressure; negligible solid and fluid lateral pressure. Secondly, for a thin debris ow height, we also construct the fourth set of eigenvalues in three different cases. These phase-eigenvalues incorporate strong interaction between the solid and fluid dynamics. The simulation results are produced by taking all these different sets of coupled phase-eigenvalues and are compared with the classical uncoupled set of solid and fluid eigenvalues. The results indicate the importance of phase-eigenvalues and supports for a complete description of the phase- eigenvalues for the enhanced description of real two-phase debris flows and landslide motions.

scholarly journals A two-phase model for numerical simulation of debris flows

2014 ◽  
Vol 2 (3) ◽  
pp. 2151-2183 ◽  
Author(s):  
S. He ◽  
W. Liu ◽  
C. Ouyang ◽  
X. Li
Keyword(s):  
Debris Flow ◽  
Debris Flows ◽  
Volume Fraction ◽  
Solid Phase ◽  
Fluid Phase ◽  
Viscous Drag ◽  
Finite Volume Scheme ◽  
Viscous Stress ◽  
Two Phase ◽  
One Dimensional

Abstract. Debris flows are multiphase, gravity-driven flows consisting of randomly dispersed interacting phases. The interaction between the solid phase and liquid phase plays a significant role on debris flow motion. This paper presents a new two-phase debris flow model based on the shallow water assumption and depth-average integration. The model employs the Mohr–Coulomb plasticity for the solid stress, and the fluid stress is modeled as a Newtonian viscous stress. The interfacial momentum transfer includes viscous drag, buoyancy and interaction force between solid phase and fluid phase. We solve numerically the one-dimensional model equations by a high-resolution finite volume scheme based on a Roe-type Riemann solver. The model and the numerical method are validated by using one-dimensional dam-break problem. The influences of volume fraction on the motion of debris flow are discussed and comparison between the present model and Pitman's model is presented. Results of numerical experiments demonstrate that viscous stress of fluid phase has significant effect in the process of movement of debris flow and volume fraction of solid phase significantly affects the debris flow dynamics.

Kinematic and Dynamic Parameters of a Liquid-Solid Pipe Flow Using DPIV∕Accelerometry

2007 ◽  
Vol 129 (11) ◽  
pp. 1415-1421 ◽  
Author(s):  
Joseph Borowsky ◽  
Timothy Wei
Keyword(s):  
Pipe Flow ◽  
Solid Phase ◽  
Fluid Phase ◽  
Central Moment ◽  
Steady Flows ◽  
Dynamic Parameters ◽  
Two Phase ◽  
Turbulence Structures ◽  
Two Phases ◽  
Flat Profile

An experimental investigation of a two-phase pipe flow was undertaken to study kinematic and dynamic parameters of the fluid and solid phases. To accomplish this, a two-color digital particle image velocimetry and accelerometry (DPIV∕DPIA) methodology was used to measure velocity and acceleration fields of the fluid phase and solid phase simultaneously. The simultaneous, two-color DPIV∕DPIA measurements provided information on the changing characteristics of two-phase flow kinematic and dynamic quantities. Analysis of kinematic terms indicated that turbulence was suppressed due to the presence of the solid phase. Dynamic considerations focused on the second and third central moments of temporal acceleration for both phases. For the condition studied, the distribution across the tube of the second central moment of acceleration indicated a higher value for the solid phase than the fluid phase; both phases had increased values near the wall. The third central moment statistic of acceleration showed a variation between the two phases with the fluid phase having an oscillatory-type profile across the tube and the solid phase having a fairly flat profile. The differences in second and third central moment profiles between the two phases are attributed to the inertia of each particle type and its response to turbulence structures. Analysis of acceleration statistics provides another approach to characterize flow fields and gives some insight into the flow structures, even for steady flows.

Evaluation of Flow Characteristics in an Oil-Water Separator Using Computational Fluid Dynamics

2020 ◽  
Author(s):  
Terry Potter ◽  
Tathagata Acharya
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Residence Time ◽  
Water Volume ◽  
Multiphase Model ◽  
Two Phase ◽  
Water Separator ◽  
Oil Water ◽  
Simulation Results ◽  
Water Cut

Abstract Multiphase separators on production platforms are among the first equipment through which well fluids flow. Based on functionality, multiphase separators can either be two-phase that separate oil from water, or three-phase that separate oil, natural gas, and water. Separator performances are often evaluated using mean residence time (MRT) of the hydrocarbon phase. MRT is defined as the amount of time a given phase stays inside the separator. On field, operators usually measure MRT as the ratio of active volume occupied by each phase to the phase volumetric flowrate. However, this method may involve significant errors as the oil-water interface height is obtained using level controllers and the volume occupied by each phase is calculated assuming the interface can be extrapolated from the weir back to the separator inlet. In this study, authors perform computational fluid dynamics (CFD) on a two-phase horizontal separator to evaluate MRT as a function of varying water volume flowrates (water-cut) in a mixture of water and oil. The authors use residence time distributions (RTD) to obtain MRT at each water-cut — a method that results in significantly more accurate results than the regular method used by operators. The numerical model is developed with commercial software package ANSYS Fluent. The code uses the Eulerian multiphase model along with the k-ε turbulence model. The simulation results show agreement with experiments performed by previous researchers. Additional simulations are performed to assess the effect of various separator internals on separator performance. Simulation results suggest that the model developed in this study can be used to predict performances of two-phase liquid-liquid separators with reasonable accuracy and will be useful towards their design to improve performances under various inlet flow conditions.

Heat Transfer in Fixed Bed Elliptic Cylindrical Reactor via Two-Phase Model

2020 ◽  
Vol 400 ◽  
pp. 45-50
Author(s):  
Antonildo Santos Pereira ◽  
Rodrigo Moura da Silva ◽  
Maria Conceição Nóbrega Machado ◽  
Luan Pedro Melo Azerêdo ◽  
Anderson Ferreira Vilela ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Solid Phase ◽  
Homogeneous Model ◽  
Fixed Bed ◽  
Fluid Phase ◽  
Packed Bed ◽  
Two Phase ◽  
Heterogeneous Model ◽  
Fully Implicit ◽  
Cylindrical Reactor

The study of heat transfer in fixed bed tubular reactors of heated or cooled walls has presented great interest by the academy and industry. The adequate and safe design of such equipment requires the use of reliable and realistic mathematical. Unfortunately several studies are restrict to homogeneous model applied to circular and elliptic cylindrical reactors. Then, the objective of this work was to predict heat transfer in packed-bed elliptic cylindrical reactor, by using a proposed heterogeneous model. The mathematical model is composed for one solid phase and another fluid phase, in which the balance equation for each constituent is applied separately. The finite volume method was utilized to solve the partial differential equations using the WUDS scheme for interpolation of the convective and diffusive terms, and the fully implicit formulation. Results of the temperature distribution of the fluid and solid phases along the reactor are presented and analyzed. It was verified that the highest temperature gradients of the phases are located close to the wall and inlet of the reactor.

scholarly journals Computational simulation of soybean particles flow in a hopper using computational fluid dynamics (CFD) and discrete elements method (DEM)

2020 ◽  
Vol 9 (8) ◽  
pp. e448985463
Author(s):  
Jéssica Aparecida Apolinário de Paula ◽  
Érica Victor de Faria ◽  
Ana Christina Pitard Lima ◽  
José Luiz Vieira Neto ◽  
Kássia Graciele dos Santos
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Computational Models ◽  
Solid Phase ◽  
Computational Simulation ◽  
Fluid Phase ◽  
Discrete Elements ◽  
Granular Dynamics ◽  
Computational Fluid Dynamics Cfd ◽  
The Subject

The hoppers are the most common structures used in storage units for agricultural products such as grains and cereals. The soybean, which is one of the most common products in Brazil spend most of their time in a hopper between the stages of picking and shipment. Problems such as damage to the hopper structures during the outflow are factors that have been the subject of studies using computational models. Computational Fluid Dynamics (CFD) has played a big role in gas-solid systems study, together with the Discrete Element Method (DEM). This method manages both fluid phase as the solid phase, which in this case is granular, through the Eulerian and Lagrangian approach. The DEM is based on the interaction between the particles and each one is separately monitored. This work aims to calibrate the parameters of the spring-dashpot model, in the granular dynamics of fluids study, which influences the contact between the soy particles in the silo. For this purpose, a comparison was made of the experimental discharge time of soybeans into a hopper, with the time resulting from 27 simulations generated by a central composite design (CCD). Through the analysis of the simulations and statistics, it was possible to identify the factors that influence whether or not the time of discharge and establish a calibration of these parameters that best describe the experimental results.

Determination of Anisotropic Absorption and Extinction Coefficients of a Tomographed Real Porous Medium

2004 ◽  
Author(s):  
Barbar Zeghondy ◽  
Jean Taine ◽  
Estelle Iacona
Keyword(s):  
Solid Phase ◽  
Fluid Phase ◽  
Radiative Properties ◽  
High Porosity ◽  
Absorption Coefficients ◽  
Extinction Coefficients ◽  
X Ray ◽  
Isotropic Media ◽  
Transfer Method

The direct general identification method of the radiative properties of high porosity media, developed and validated for virtual statistically isotropic media in [1], has been applied to a real statistically anisotropic medium. This medium has a transparent fluid phase and an opaque gray diffuse solid phase. It is modelled by a semi-transparent equivalent medium characterized by extinction and absorption coefficients β and κ. These quantities are directly determined from the morphology data obtained by X-ray tomography and from the absorptivity of the solid phase. The application of this approach to a mullite sample has established that β and κ are homogeneous but depend on direction. This last feature has to be accounted for by a radiative transfer method for this type of medium.

scholarly journals Investigation of the Primary Phase Segregation during the Filling of an Industrial Mold with Semi-Solid A357 Aluminum

2008 ◽  
Vol 141-143 ◽  
pp. 635-640 ◽  
Author(s):  
Frédéric Pineau ◽  
Geneviève Simard
Keyword(s):  
Phase Distribution ◽  
Solid Phase ◽  
Numerical Models ◽  
Phase Segregation ◽  
Homogeneous Distribution ◽  
Phase Interaction ◽  
Two Phase ◽  
Cast Part ◽  
Α Phase ◽  
Semi Solid

Casting metal alloys in the semi-solid state is now becoming a well established manufacturing technique. But, the success of this technology necessitates a good understanding of the feedstock material behaviour. To obtain high quality components with semi-solid metal processing, a homogeneous distribution of phases must be maintained in the material during the die filling stage. Many parameters affect the process such as temperature, time and stress history, which influence the shape, size and connectivity of the particles that make up the slurry. The subsequent phase interaction mechanisms are quite complex and have direct effects on the flow and final micro-structure distribution of the cast part and thus, without any doubt, on its mechanical properties. Two-phase numerical models have been developed to account for the liquid-solid phase separation e.g. [1,2]. Several two-phase models have been elaborated on the basis of soil mechanics and consider that the phase interaction term is mainly due to the flow through a porous medium. Because of the difficulties of making direct measurements in an extremely hostile environment, there has been very little work done to validate these models. In order to fill this gap, a better understanding of the phase distribution and phase segregation mechanisms during the filling step is required. In this work, the post-solidification primary α-phase distribution inside an industrial semi-solid cast part has thus been investigated. A thorough metallographic analysis has been performed using an upright microscope coupled to a Clemex image-analysis software. The results were then processed to produce a map of the final α-phase distribution. Many different grain scales have been observed in the solidified part and their distributions seem to be closely associated to the velocity field. Contacts between moving particles seem to play an important role in the phase distribution and show many similarities to granular materials. This latter aspect should be considered in the development of new constitutive models for semi-solid slurries.

Numerical Modelling of Net Motion in Waves and Current Using CFD

2019 ◽  
Author(s):  
Tobias Martin ◽  
Arun Kamath ◽  
Hans Bihs
Keyword(s):  
Fluid Dynamics ◽  
Numerical Model ◽  
Cfd Model ◽  
Time Step ◽  
Two Phase ◽  
Fluid Forces ◽  
Open Sea ◽  
Geometrical Constraints ◽  
Static Approach

Abstract The structural and environmental challenges in the operation of marine fish cage structures, in particular in the open sea, can accurately be determined if the fluid dynamics in and around the whole system is studied. An important part of the system represents the porous net which encloses the fish. In this paper, a numerical model for the determination of the deformed shape of nets under consideration of hydrodynamic loads and elastic twines is elaborated. It is a quasi-static approach based on force equilibria at the knots and geometrical constraints. The missing time step restriction leads to an overall less costly computation. The fluid around the net is calculated using a two-phase CFD model. The focus of the research is on the calculation of fluid forces on the net and the analyses of the nets motion in current and waves.

Equations of Motion of Two-Phase Variable Mass Systems With Solid Base

1994 ◽  
Vol 61 (4) ◽  
pp. 855-860 ◽  
Author(s):  
F. O. Eke ◽  
Song-Min Wang
Keyword(s):  
Solid Phase ◽  
Equations Of Motion ◽  
Variable Mass ◽  
Fluid Phase ◽  
Solid Base ◽  
Phase Variable ◽  
Dynamical Equations ◽  
Two Phase ◽  
Attitude Stability ◽  
Variable Mass Systems

This paper develops dynamical equations for variable mass systems that can be viewed, at any given instant, as comprising a solid phase and a fluid phase. The equations of translational and rotational motion are presented, and several versions of each are given. It is shown that some versions have major advantages over others because they involve parameters that are relatively easy to estimate in practical problems, and make close-form solutions possible without the usual penalty of drastic simplifying assumptions. A simple rocket example is presented, and shows that instability cannot be ruled out for such systems. It is shown that system and combustion chamber geometry play a crucial role in the attitude stability of such systems.

A Two-Phase CFD Modeling Approach to Investigate the Flow Characteristics in Radial Flow Moving-Bed Reactors

2014 ◽  
Vol 12 (1) ◽  
pp. 497-512 ◽  
Author(s):  
Fang-Zhi Xiao ◽  
Zheng-Hong Luo
Keyword(s):  
Radial Flow ◽  
Solid Phase ◽  
Flow Behavior ◽  
Flow Characteristics ◽  
Cfd Modeling ◽  
Reactor Model ◽  
Two Phase ◽  
Moving Bed ◽  
Porous Media Model ◽  
Simulation Results

Abstract Based on a complete CFD Eulerian–Eulerian two-fluid approach, a comprehensive three-dimensional (3D) two-phase reactor model was suggested to describe the flow behavior in radial flow moving-bed reactors (RFMBRs). A porous media model was incorporated into the reactor model in order to describe the flow resistance provided by the porous walls of the center and annular pipes. Compared with these previous reactor models, the reactor model considers the solid-phase movement instead of immobilization, which benefits for predicting the formation of cavity practically. The simulation results are agreement with the published experimental data. By employing the verified model, the flow field parameters in the reactors such as pressure drop and flow velocity were obtained. Besides, the simulations were then carried out to investigate the effect of the bed voidage on the flow behavior and to understand the phenomenon of cavity in the RFMBRs. The simulation results showed that both the centripetal and the centrifugal flow configurations have the inhomogeneous flow distribution and the phenomenon of cavity. Furthermore, the inhomogeneous distribution increases with the increase of the bed voidage, whereas the phenomenon of cavity is more obvious with the increase of gas inlet velocity. As a whole, this work provided a realistic modeling and a useful approach for the understanding of RFMBRs.

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