Slug generation processes in co-current turbulent-gas/laminar-liquid flows in horizontal channels

We theoretically and computationally investigate the physical processes of slug-flow development in concurrent two-phase turbulent-gas/laminar-liquid flows in horizontal channels. The objective is to understand the fundamental mechanisms governing the initial growth and subsequent nonlinear evolution of interfacial waves, starting from a smooth stratified flow of two fluids with disparity in density and viscosity and ultimately leading to the formation of intermittent slug flow. We numerically simulate the entire slug development by means of a fully coupled immersed flow (FCIF) solver that couples the two disparate flow dynamics through an immersed boundary (IB) method. From the analysis of spatial/temporal interface evolution, we find that slugs develop through three major cascading processes: (I) stratified-to-wavy transition; (II) development and coalescence of long solitary waves; and (III) rapid channel bridging leading to slugging. In Process I, relatively short interfacial waves form on the smooth interface, whose growth is governed by the Orr–Sommerfeld instability. In Process II, interfacial waves evolve into long solitary waves through multiple resonant and near-resonant wave–wave interactions. From instability analysis of periodic solitary waves, we show that these waves are unstable to their subharmonic disturbances and grow in amplitude and primary wavelength through wave coalescence. The interfacial forcing from the turbulent gas–laminar liquid interactions significantly precipitates the growth of instability of solitary waves and enhances coalescence of solitary waves. In Process III, we show by an asymptotic analysis that interfacial waves achieve multiple-exponential growth right before bridging the channel, consistent with observations in existing experiments. The present study provides important insights for effective modelling of slug-flow dynamics and the prediction of slug frequency and length, important for design and operation of (heavy-oil/gas) pipelines and production facilities.

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Large-Eddy Simulation of turbulent, cavitating fuel flow inside a 9-hole Diesel injector including needle movement

International Journal of Engine Research ◽

10.1177/1468087416643901 ◽

2016 ◽

Vol 18 (3) ◽

pp. 195-211 ◽

Cited By ~ 20

Author(s):

Felix Örley ◽

Stefan Hickel ◽

Steffen J Schmidt ◽

Nikolaus A Adams

Keyword(s):

Large Eddy Simulation ◽

Fluid Model ◽

Immersed Boundary ◽

Small Scale ◽

Two Phase ◽

Eddy Simulation ◽

Large Eddy ◽

Flow Features ◽

Two Fluid Model ◽

Liquid Flows

We investigate the turbulent multiphase flow inside a nine-hole common rail Diesel injector during a full injection cycle of ISO 4113 diesel fuel into air by implicit large-eddy simulation (LES). The simulation includes a prescribed needle movement obtained from a one-dimensional multi-domain simulation. The injector geometry is represented by a conservative cut-element-based immersed boundary method with subcell resolution, which has been developed for the application in the context of cavitating liquid flows. We employ a barotropic two-phase two-fluid model, where all components (i.e. air, liquid diesel, gaseous diesel) are represented by a homogenous mixture approach. The cavitation model is based on a thermodynamic equilibrium assumption. Compressibility of all phases enables full resolution of collapse-induced pressure wave dynamics. The analysis of the turbulent flow field reveals that the opening and closing phase are dominated by small-scale turbulence, while in the main injection phase large vortical structures are formed in the needle volume and reach into the nozzle holes. Violent collapse events of cavitation structures are detected during the closing phase in the nozzle holes and after closing in the sac hole region. A comparison with LES results with a fixed injector needle at different lift positions shows a good agreement for large needle lifts, while the needle movement has significant effects on important flow features at low needle lifts.

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On the Dynamic Response of Flexible Risers Caused by Internal Slug Flow

Volume 5: Ocean Engineering; CFD and VIV ◽

10.1115/omae2012-83316 ◽

2012 ◽

Cited By ~ 3

Author(s):

Arturo Ortega ◽

Ausberto Rivera ◽

Ole Jørgen Nydal ◽

Carl M. Larsen

Keyword(s):

Finite Element ◽

Dynamic Response ◽

Slug Flow ◽

Time Integration ◽

Flow Dynamics ◽

Two Phase ◽

Structural Dynamic ◽

Linear Finite Element ◽

Flow Through ◽

Flexible Risers

Slug flow through flexible risers is a frequent phenomenon which occurs during production of a mixture of oil and gas. The dynamic nature of the slug pattern induces time varying forces, which leads to structural vibrations of the riser. These vibrations can produce large deflections and stresses, which can leave it to fail by fatigue, excessive bending or local buckling. In this work the influence from slug flow on the structural dynamic response of a lazy wave flexible riser is analyzed using a computational tool consisting of one program for calculation of slug flow dynamics, and another program for structural dynamic response. Both programs apply a time integration method, and since slug flow will lead to dynamic motion response of the riser, and riser motion dynamics will influence slug flow dynamics, the two codes need to exchange information during the integration process. Information exchange is established by making a federation based on High Level Architecture (HLA). The federation is composed of SLUGIT and RISANANL. SLUGGIT is a two-phase flow code written in C++ which simulates dynamic slug flow through pipes and riser using a Lagrangian tracking model. RISANANL is a FORTRAN program for static and dynamic structural analysis of slender marine structures based on a finite element formulation. Using the HLA standard these two programs can carry out synchronized time integration and exchange information for each time step. In this work the structural analysis code accomplishes the dynamic response using a linear finite element (FE) formulation. Hence, forces from centripetal acceleration of the internal flow, relative velocity between the riser and surrounding water, and varying gravity of the pipe and content will be accounted for in the dynamic analysis. Displacements, stresses, internal pressure, and outlet flow rates of liquid and gas will be accounted for. The results encourage us to carry out a fully non-linear finite element analysis, in order to have a better understanding of the dynamic behaviour of flexible risers undergoing an unsteady internal two-phase flow.

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COMPUTATIONAL FLUID DYNAMICS SIMULATION OF WATER-OIL TWO-PHASE SLUG FLOW IN MICROCHANNELS

Interfacial Phenomena and Heat Transfer ◽

10.1615/interfacphenomheattransfer.2020032281 ◽

2019 ◽

Vol 7 (4) ◽

pp. 365-376

Author(s):

Shan Wang ◽

Lei Liu ◽

Si Wei ◽

Dongxu Liu

Keyword(s):

Fluid Dynamics ◽

Computational Fluid Dynamics ◽

Slug Flow ◽

Dynamics Simulation ◽

Computational Fluid Dynamics Simulation ◽

Two Phase

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Behaviour of air injection nozzles in dissolved air flotation

Water Science & Technology ◽

10.2166/wst.1995.0513 ◽

1995 ◽

Vol 31 (3-4) ◽

pp. 25-35 ◽

Cited By ~ 12

Author(s):

E. M. Rykaart ◽

J. Haarhoff

Keyword(s):

Bubble Coalescence ◽

Second Phase ◽

Initial Growth ◽

Two Phase ◽

Dissolved Air Flotation ◽

Nozzle Orifice ◽

Pressure Release ◽

Air Volume ◽

Air Flotation ◽

Dissolved Air

A simple two-phase conceptual model is postulated to explain the initial growth of microbubbles after pressure release in dissolved air flotation. During the first phase bubbles merely expand from existing nucleation centres as air precipitates from solution, without bubble coalescence. This phase ends when all excess air is transferred to the gas phase. During the second phase, the total air volume remains the same, but bubbles continue to grow due to bubble coalescence. This model is used to explain the results from experiments where three different nozzle variations were tested, namely a nozzle with an impinging surface immediately outside the nozzle orifice, a nozzle with a bend in the nozzle channel, and a nozzle with a tapering outlet immediately outside the nozzle orifice. From these experiments, it is inferred that the first phase of bubble growth is completed at approximately 1.7 ms after the start of pressure release.

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On Instabilities in Horizontal Two-Phase Flow

Collection of Czechoslovak Chemical Communications ◽

10.1135/cccc19942595 ◽

1994 ◽

Vol 59 (12) ◽

pp. 2595-2603

Author(s):

Lothar Ebner ◽

Marie Fialová

Keyword(s):

Differential Equation ◽

Flow Regime ◽

Slug Flow ◽

Annular Flow ◽

Two Phase Flow ◽

Phase Flow ◽

Two Phase ◽

Annular Flows ◽

Flow Regime Maps

Two regions of instabilities in horizontal two-phase flow were detected. The first was found in the transition from slug to annular flow, the second between stratified and slug flow. The existence of oscillations between the slug and annular flows can explain the differences in the limitation of the slug flow in flow regime maps proposed by different authors. Coexistence of these two regimes is similar to bistable behaviour of some differential equation solutions.

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