Recent developments in hydrodynamic stability of two-phase flows

2012 ◽  
Vol 9 (1) ◽  
pp. 125-130
Author(s):  
A.N. Osiptsov ◽  
S.A. Boronin
Keyword(s):  
Boundary Layer ◽  
Particle Concentration ◽  
Volume Fraction ◽  
Time Interval ◽  
Dusty Gas ◽  
Two Phase Flows ◽  
Two Phase ◽  
Layer Width ◽  
Dispersed Flows ◽  
Optimal Disturbances

In the framework of two-continuum model, the stability of plane-parallel dispersed flows is analyzed. Several flow configurations are considered and several new factors are analyzed. The factors include: particle velocity slip and particle concentration non-uniformity in the main flow, non-Stokesian components of the interphase force and finite volume fraction of the dispersed phase. It is found that the new factors modify significantly the parameters of the fastest growing mode and change the critical Reynolds number of two-phase flows. A method for studying algebraic (non-modal) instability and optimal disturbances to dispersed flows is proposed. While studying the non-modal instability of the dusty-gas boundary-layer flow with a non-uniform particle concentration, we found that the disturbances with the maximum energy gain at a limited time interval are streamwise-elongated structures (streaks). As compared to the flow of a particle-free fluid, optimal disturbances to the dusty-gas flow gain much larger kinetic energy even at the boundary layer width-averaged mass concentration of ten percent, which leads to significant amplification of non-modal instability mechanism due to the presence of suspended particles.

scholarly journals Simulation of the Effect of Oil Volume Fractions in an Oil-Water Flows Along a Circular Pipe: A Finite Element Approach

2018 ◽  
Vol 10 (5) ◽  
pp. 19
Author(s):  
Ferdusee Akter ◽  
Md. Bhuyan ◽  
Ujjwal Deb
Keyword(s):  
Finite Element ◽  
Volume Fraction ◽  
Fluid Velocity ◽  
Galerkin Approximation ◽  
Computational Domain ◽  
Two Phase Flows ◽  
Two Phase ◽  
Volume Fractions ◽  
Oil In Water ◽  
Element Approach

Two phase flows in pipelines are very common in industries for the oil transportations. The aim of our work is to observe the effect of oil volume fraction in the oil in water two phase flows. The study has been accomplished using a computational model which is based on a Finite Element Method (FEM) named Galerkin approximation. The velocity profiles and volume fractions are performed by numerical simulations and we have considered the COMSOL Multiphysics Software version 4.2a for our simulation. The computational domain is 8m in length and 0.05m in radius. The results show that the velocity of the mixture decreases as the oil volume fraction increases. It should be noted that if we gradually increase the volume fractions of oil, the fluid velocity also changes and the saturated level of the volume fraction is 22.3%.

A Combined Volume of Fluid and Immersed Boundary Method for Modelling of Two-Phase Flows with High Density Ratio

2021 ◽  
Author(s):  
Qiu Jin ◽  
Dominic Hudson ◽  
W.G. Price
Keyword(s):  
Boundary Layer ◽  
Immersed Boundary Method ◽  
Density Ratio ◽  
Volume Of Fluid ◽  
High Density ◽  
Immersed Boundary ◽  
Two Phase Flows ◽  
Two Phase ◽  
Boundary Method ◽  
High Density Ratio

Abstract A combined volume of fluid and immersed boundary method is developed to simulate two-phase flows with high density ratio. The problems of discontinuity of density and momentum flux are known to be challenging in simulations. In order to overcome the numerical instabilities, an extra velocity field is designed to extend velocity of the heavier phase into the lighter phase and to enforce a new boundary condition near the interface, which is similar to non-slip boundary conditions in Fluid-Structure Interaction (FSI) problems. The interface is captured using a Volume of Fluid (VOF) method, and a new boundary layer is built on the lighter phase side by an immersed boundary method. The designed boundary layer helps to reduce the spurious velocity caused by the imbalance of dynamic pressure gradient and density gradient and to prevent tearing of the interface due to the tangential velocity across the interface. The influence of time step, density ratio, and spatial resolution is studied in detail for two set of cases, steady stratified flow and convection of a high-density droplet, where direct comparison is possible to potential flow analysis (i.e. infinite Reynold's number). An initial study for a droplet splashing on a thin liquid film demonstrates applicability of the new solver to real-life applications. Detailed comparisons should be performed in the future for finite Reynold's number cases to fully demonstrate the improvements in accuracy and stability of high-density ratio two-phase flow simulations offered by the new method.

Kinematic-wave theory of sedimentation beneath inclined walls

1982 ◽  
Vol 120 ◽  
pp. 323-346 ◽  
Author(s):  
W. Schneider
Keyword(s):  
Boundary Layer ◽  
Boundary Layer Flow ◽  
Particle Concentration ◽  
Wave Theory ◽  
Basic Flow ◽  
Kinematic Wave ◽  
Wave Fronts ◽  
Two Phase ◽  
Continuous Increase ◽  
Layer Flow

The two-phase flow in settling vessels with walls that are inclined to the vertical is investigated. By neglecting inertial effects and the viscosity of the suspension i t is shown that the particle concentration remains constant on kinematic-wave fronts. The wave fronts are horizontal and propagate in a quasi-one-dimensional manner, but are imbedded in a two-dimensional or three-dimensional basic flow which, in turn, depends on the waves via the boundary conditions. Concentration discontinuities (interfaces) are described by kinematic-shock theory. The kinematic shocks are shown to be horizontal, with the possible exception of discontinuities that separate the suspension from the sediment.At downward-facing inclined walls conservation of mass enforces the existence of a boundary-layer flow with relatively large velocity. As G/R2→∞ and G/R4→ 0, where G and R are respectively a sedimentation Grashof number and a sedimentation Reynolds number, the entrainment of suspended particles into the boundary-layer flow of clear liquid is negligibly small. This provides an appropriate boundary condi- tion for the basic flow of the suspension. Thus, in the double limit considered, a kine- matic theory suffices to determine the convective flow of the suspension due to the presence of inclined walls.As an example batch sedimentation in vessels with inclined plane or conical walls is investigated. The settling process is terminated after a time that can be considerably smaller than the time required in a vertical vessel under the same conditions.Depending on the initial particle concentration, there are centred kinematic waves that are linked to a continuous increase of the particle concentration in the suspension. In an appendix, the flow in the boundary layer at a downward facing, inclined wall is investigated. With G/R2→∞ and G/R4→ 0, the boundary layer consists of an inviscid particle-free main part, a viscous sublayer at the wall, and a free shear sublayer at the liquid/particle interface.

scholarly journals Wake attenuation in large Reynolds number dispersed two-phase flows

2008 ◽  
Vol 366 (1873) ◽  
pp. 2177-2190 ◽  
Author(s):  
Frédéric Risso ◽  
Véronique Roig ◽  
Zouhir Amoura ◽  
Guillaume Riboux ◽  
Anne-Marie Billet
Keyword(s):  
Reynolds Number ◽  
Volume Fraction ◽  
Bubble Diameter ◽  
Temporal Variations ◽  
The Body ◽  
Experimental Investigations ◽  
Large Reynolds Number ◽  
Two Phase Flows ◽  
Two Phase ◽  
Multi Body

The dynamics of high Reynolds number-dispersed two-phase flow strongly depends on the wakes generated behind the moving bodies that constitute the dispersed phase. The length of these wakes is considerably reduced compared with those developing behind isolated bodies. In this paper, this wake attenuation is studied from several complementary experimental investigations with the aim of determining how it depends on the body Reynolds number and the volume fraction α . It is first shown that the wakes inside a homogeneous swarm of rising bubbles decay exponentially with a characteristic length that scales as the ratio of the bubble diameter d to the drag coefficient C d , and surprisingly does not depend on α for 10 −2 ≤ α ≤10 −1 . The attenuation of the wakes in a fixed array of spheres randomly distributed in space ( α =2×10 −2 ) is observed to be stronger than that of the wake of an isolated sphere in a turbulent incident flow, but similar to that of bubbles within a homogeneous swarm. It thus appears that the wakes in dispersed two-phase flows are controlled by multi-body interactions, which cause a much faster decay than turbulent fluctuations having the same energy and integral length scale. Decomposition of velocity fluctuations into a contribution related to temporal variations and that associated to the random character of the body positions is proposed as a perspective for studying the mechanisms responsible for multi-body interactions.

scholarly journals Global Solvability of Compressible–Incompressible Two-Phase Flows with Phase Transitions in Bounded Domains

Mathematics ◽  
2021 ◽  
Vol 9 (3) ◽  
pp. 258
Author(s):  
Keiichi Watanabe
Keyword(s):  
Free Boundary ◽  
Boundary Problem ◽  
Free Boundary Problem ◽  
Global Solvability ◽  
Time Interval ◽  
Bounded Domains ◽  
Two Phase Flows ◽  
Two Phase ◽  
Unique Existence ◽  
A Free Boundary Problem

Consider a free boundary problem of compressible-incompressible two-phase flows with surface tension and phase transition in bounded domains Ωt+,Ωt−⊂RN, N≥2, where the domains are separated by a sharp compact interface Γt⊂RN−1. We prove a global in time unique existence theorem for such free boundary problem under the assumption that the initial data are sufficiently small and the initial domain of the incompressible fluid is close to a ball. In particular, we obtain the solution in the maximal Lp−Lq-regularity class with 2<p<∞ and N<q<∞ and exponential stability of the corresponding analytic semigroup on the infinite time interval.

Measurement of a Void Fraction in Bubbly Gas-Water Two Phase Flows Using Differential Pressure Technique

2012 ◽  
Vol 152-154 ◽  
pp. 1221-1226
Author(s):  
H.A.M. Hasan Abbas
Keyword(s):  
Experimental Study ◽  
Void Fraction ◽  
Volume Fraction ◽  
Differential Pressure ◽  
Flow Density ◽  
Two Phase Flows ◽  
Two Phase ◽  
Gas Volume Fraction ◽  
Fraction Measurement ◽  
Gas Volume

Multiphase flows, where two or even three fluids flow simultaneously in a pipe are becoming increasingly important in industry. In order to measure the flow rate of gas-water two phase flows accurately, the void fraction (gas volume fraction) in two phase flows must be precisely measured. The differential pressure technique has proven attractive in the measurement of volume fraction. This paper presents the theoretical and experimental study of the void fraction measurement in bubbly gas water two phase flows using differential pressure technique (the flow density meter).

scholarly journals NUMERICAL MODELING OF TWO-PHASE FLOWS USING THE TWO-FLUID TWO-PRESSURE APPROACH

2004 ◽  
Vol 14 (05) ◽  
pp. 663-700 ◽  
Author(s):  
THIERRY GALLOUËT ◽  
JEAN-MARC HÉRARD ◽  
NICOLAS SEGUIN
Keyword(s):  
Volume Fraction ◽  
Local Equilibrium ◽  
Finite Volume Methods ◽  
Convective System ◽  
Two Phase Flows ◽  
Step Method ◽  
Discontinuous Solutions ◽  
Fractional Step Method ◽  
Two Phase ◽  
Two Fluid

The present paper is devoted to the computation of two-phase flows using the two-fluid approach. The overall model is hyperbolic and has no conservative form. No instantaneous local equilibrium between phases is assumed, which results in a two-velocity two-pressure model. Original closure laws for interfacial velocity and interfacial pressure are proposed. These closures allow to deal with discontinuous solutions such as shock waves and contact discontinuities without ambiguity with the definition of Rankine–Hugoniot jump relations. Each field of the convective system is investigated, providing maximum principle for the volume fraction and the positivity of densities and internal energies are ensured when focusing on the Riemann problem. Two-finite volume methods are presented, based on the Rusanov scheme and on an approximate Godunov scheme. Relaxation terms are taken into account using a fractional step method. Eventually, numerical tests illustrate the ability of both methods to compute two-phase flows.

scholarly journals Re-Reflection Effect On Shock Waves in Two-Phase Flows through a Tube of Variable Cross-Section

2018 ◽  
Vol 3 (12) ◽  
pp. 67-73
Author(s):  
Kanti Pandey
Keyword(s):  
Cross Section ◽  
Volume Fraction ◽  
Particle Volume Fraction ◽  
Variable Cross Section ◽  
Variable Cross ◽  
Reflection Effect ◽  
Two Phase Flows ◽  
Particle Volume ◽  
Two Phase ◽  
Cross Sectional

In present paper Re-reflection  effect on  shock –waves in two-phase flows through a tube of variable cross-section is considered when particle  volume fraction appeared as an additional variable .It is concluded that re-reflected effects reduce the cross sectional  area .For two-phase flows when equilibrium is eventually established , presence of particle volume fraction , further reduce  the cross – sectional area. One dimensional area relation for a non – uniform , steady flow ahead of a shock   is obtained and concluded that  all the results are valid for the case   when  direction of the shock motion and the gas flow ahead of the  shock is same  .  In preparation of graphs Mathematica 7 is used .

An Experimental Study on the Cuttings Transport in Inclined Slim-Hole Annulus

2012 ◽  
Author(s):  
Y. J. Kim ◽  
S. M. Han ◽  
N. S. Woo
Keyword(s):  
Particle Concentration ◽  
Volume Fraction ◽  
Particle Volume Fraction ◽  
Flow Characteristics ◽  
Directional Drilling ◽  
Cuttings Transport ◽  
Particle Volume ◽  
Two Phase ◽  
Solid Liquid ◽  
And Control

In directional drilling, it is difficult to adjust and control the cuttings, so it is very important to evaluate the flow characteristics of a drilling flow field. In this study, solid-liquid two-phase flow experiments have been carried out in non-Newtonian fluids for hole inclinations from vertical to 75 degrees, flow velocities from 0.33 m/s to 0.66 m/s, particle concentration from 4 to 16 %, and pipe rotations from 0 to 400 rpm. Pressure drop within the test section, and particle volume fraction are measured for the above test conditions. These quantities were influenced by particle concentration within the flow, pipe rotation, flow volume, and inclination of the annulus. Moreover, empirical correlations were developed for estimating friction coefficient and particle volume fraction inside annulus. The new correlations generated in this study are believed to be very practical and handy when they are used in the field. Therefore, this study can provide meaningful data for directional drillings.

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