Upward bubbly flows in a square pipe with a sudden expansion: Bubble dispersion and reattachment length

Numerical simulations are performed to study three-dimensional hydrodynamic flows in a sudden expansion of rectangular ducts. Separation phenomena are investigated through the analysis of flow topology and streamline patterns. Scaling laws describing the evolution of the reattachment length of the vortical areas that appear behind the cross-section enlargement are derived. The results discussed in this paper are required as a starting point to investigate the effects of an applied homogeneous magnetic field on separation phenomena in a geometry with a sudden expansion.

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The Axisymmetric Sudden Expansion Flow of a Non-Newtonian Viscoplastic Fluid

Journal of Fluids Engineering ◽

10.1115/1.2819108 ◽

1997 ◽

Vol 119 (1) ◽

pp. 193-200 ◽

Cited By ~ 27

Author(s):

G. C. Vradis ◽

M. V. O¨tu¨gen

Keyword(s):

Reynolds Numbers ◽

Bingham Fluid ◽

Viscoplastic Fluid ◽

Sudden Expansion ◽

Reattachment Length ◽

Internal Flows ◽

Recirculating Flow ◽

Finite Difference Technique ◽

Wide Range ◽

Fluid Properties

The flow of a non-Newtonian viscoplastic Bingham fluid over an axisymmetric sudden expansion is studied by numerically solving the governing fully-elliptic continuity and momentum equations. Solutions are obtained for a wide range of Reynolds and yield numbers in the laminar flow regime with constant fluid properties. The present work demonstrates that the finite-difference technique can successfully be employed to obtain solutions to separating/reattaching internal flows of Bingham plastics. The results demonstrate the strong effects of the yield and Reynolds numbers on both the integral and the local structure of the separating and reattaching flow. Higher yield numbers result in larger overall effective viscosities and thus faster flow recovery downstream of the sudden expansion. The reattachment length decreases with increasing yield numbers, eventually reaching an asymptotic nonzero value which, in turn, is dependent on the Reynolds number. The strength of the recirculating flow also decreases with increasing yield numbers.

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Inlet centerline turbulence effects on reattachment length in axisymmetric sudden-expansion flows

Experiments in Fluids ◽

10.1007/bf00264409 ◽

1987 ◽

Vol 5 (6) ◽

pp. 424-426 ◽

Cited By ~ 21

Author(s):

R. M. C. So

Keyword(s):

Sudden Expansion ◽

Reattachment Length ◽

Turbulence Effects

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Efficient simulation of bubble dispersion and resulting interaction

Experimental and Computational Multiphase Flow ◽

10.1007/s42757-020-0082-2 ◽

2020 ◽

Vol 3 (3) ◽

pp. 152-170

Author(s):

Xinghao Yang ◽

Mark-Patrick Mühlhausen ◽

Jochen Fröhlich

Keyword(s):

Dispersion Model ◽

Force Balance ◽

Turbulent Dispersion ◽

Bubbly Flows ◽

Efficient Simulation ◽

Bubble Dispersion ◽

Continuous Random Walk ◽

Two Phases ◽

The One ◽

Good Agreement

Abstract In this work, an efficient model for simulating bubble dispersion and coalescence due to turbulence is developed in the Euler-Lagrange framework. The primary liquid phase is solved on the Euler grid with the RANS turbulence model. Bubble motion is computed with the force balance equations. One-way coupling between two phases is assumed and the framework is designed for the computation of disperse bubbly flows at low Eötvös number. The turbulent dispersion of the dispersed phase is reconstructed with the continuous random walk (CRW) model. Bubble-bubble collisions and coalescence are accounted for deterministically. To accelerate the time-consuming search for potential collision partners in dense bubbly flows, the sweep and prune algorithm is employed, which can be utilized in arbitrary mesh types and sizes. Validation against experiments of turbulent pipe flows demonstrates that the one-way coupled EL-CRW dispersion model can well reproduce the bubble distribution in a typical dense bubbly pipe flow. Good agreement of the bubble size distribution at the pipe outlet between the simulation and the experiment is obtained.

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Flow patterns for an annular flow over an axisymmetric sudden expansion

Journal of Fluid Mechanics ◽

10.1017/s0022112097006794 ◽

1997 ◽

Vol 350 ◽

pp. 177-188 ◽

Cited By ~ 20

Author(s):

H. J. SHEEN ◽

W. J. CHEN ◽

J. S. WU

Keyword(s):

Reynolds Number ◽

Annular Flow ◽

Laser Doppler Anemometry ◽

Flow Patterns ◽

Sudden Expansion ◽

Reattachment Length ◽

Velocity Fluctuations ◽

Recirculation Zones ◽

Flow Vortex ◽

Central Flow

In this paper, an experimental investigation is described for a concentric annular flow over an axisymmetric sudden expansion by using both flow visualization and laser-Doppler anemometry (LDA) techniques. Depending upon the value of the Reynolds number and whether the Reynolds number was increased or decreased, four typical flow patterns were classified according to the characteristics of the central and corner recirculation zones. The flow patterns are open annular flow, closed annular flow, vortex shedding, and stable central flow. Bifurcation for this flow occurred when 230 < Re < 440, which was verified by observing the variation of the reattachment length. The spatial growth of velocity fluctuations from the measurements demonstrated a tendency that shedding vortices behind the centrebody more strongly affect the reattachment length than flows without a centrebody.

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