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Conference on Turbulence and Interactions TI2006 May June Porquerolles France

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30 pages
1 Conference on Turbulence and Interactions TI2006, May 29 – June 2, 2006, Porquerolles, France Studies of Bubbly Channel Flows by Direct Numerical Simulations Gretar Tryggvason*, Jiacai Lu*, Souvik Biswas*, Asghar Esmaeeli** * Worcester Polytechnic Institute, Worcester, MA, USA ** Southern Illinois University, Carbondale, IL, USA ABSTRACT Recent DNS studies of buoyant bubbly flows in vertical channels are discussed. Simulations of nearly spherical bubbly flows in vertical channels show that the bubbles move towards the wall for upflow and away from the wall for downflow in such a way that the core is in hydrostatic equilibrium. For downflow the wall layer is free of bubbles but for upflow there is an excess of bubbles in the wall layer. The liquid velocity in the core is uniform. For laminar downflow the velocity in the wall layer can be computed analytically and for turbulent flow the velocity is given (almost) by the law of the wall. For upflow the velocity is strongly influenced by the presence of the bubbles. Results from several simulations, fully resolving the flow around each bubble, are used to discuss the effect of void fraction and bubble size for turbulent downflow. INTRODUCTION Bubbly flows in vertical pipes and channels are encountered in a wide variety of industrial systems. The best-known early study of such flows is by Serizawa, Kataoka and Michiyoshi [1,2] who examined experimentally the void fraction distribution and the velocity profile in turbulent air-water bubbly flows.

  • both uniform

  • laminar bubbly

  • flows show

  • vertical pipe

  • flows

  • bubbly flows

  • bubble size

  • multiphase flow

  • bubbles

  • wall


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DNS of Multiphase Flows
Grétar Tryggvason
Jiacai Lu and Souvik Biswas
Worcester Polytechnic Institute
Asghar Esmaeeli
Southern Illinois University
Studies of Bubbly Channel
Flows by Direct Numerical
Simulations
Conference on Turbulence and Interactions TI2006
May 29 – June 2, 2006
DNS of Multiphase Flows
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grid and the front is tracked by connected marker points
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Conservation of Momentum
Conservation of Mass
Equation of State:
Singular interface term
Incompressible flow
Computational Approach
DNS of Multiphase Flows
A. Esmaeeli and G. Tryggvason, "An Inverse Energy Cascade
in Two-Dimensional, Low Reynolds Number Bubbly
Flows."
J. Fluid Mech
. 314 (1996), 315-330.
E.A. Ervin and G. Tryggvason, "The Rise of Bubbles in a
Vertical Shear Flow."
ASME J. Fluid Engineering
119
(1997), 443-449.
A. Esmaeeli and G. Tryggvason, "Direct Numerical
Simulations of Bubbly Flows. Part I—Low Reynolds
Number Arrays."
J. Fluid Mech
. 377 (1998), 313-345.
A. Esmaeeli and G. Tryggvason, "Direct Numerical
Simulations of Bubbly Flows. Part II—Moderate
Reynolds Number Arrays"
J. Fluid Mech
. 385 (1999),
325-358.
B. Bunner and G. Tryggvason. Direct Numerical Simulations
of Three-Dimensional Bubbly Flows.
Phys. Fluids
, 11
(1999), 1967-1969.
B. Bunner and G. Tryggvason. Dynamics of Homogeneous
Bubbly Flows: Part 1. Rise Velocity and Microstructure
of the Bubbles.
J. Fluid Mech.
466 (
2002),
17-52.
B. Bunner and G. Tryggvason. Dynamics of Homogeneous
Bubbly Flows. Part 2, Fluctuations of the Bubbles and
the Liquid.
J. Fluid Mech
466 (
2002),
53-84.
B. Bunner and G. Tryggvason. G. Bunner and G. Tryggvason.
“Effect of Bubble Deformation on the Stability and
Properties of Bubbly Flows.”
J. Fluid Mech
. 495 (2003),
77-118
.
Applications of DNS to bubbly flows