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Research Papers: Multiphase Flows

Influence of Bubbles on the Turbulence Anisotropy

[+] Author and Article Information
Igor A. Bolotnov

Department of Nuclear Engineering,
North Carolina State University,
Raleigh, NC 27695

Manuscript received April 11, 2012; final manuscript received January 25, 2013; published online April 3, 2013. Assoc. Editor: Francine Battaglia.

J. Fluids Eng 135(5), 051301 (Apr 03, 2013) (9 pages) Paper No: FE-12-1188; doi: 10.1115/1.4023651 History: Received April 11, 2012; Revised January 25, 2013

Direct numerical simulation (DNS) with interface tracking of turbulent bubbly flows is becoming a major tool in advancing our knowledge in the area of multiphase modeling research. A comprehensive analysis of the turbulent flow structure allows us to evaluate the state-of-the-art computational multiphase fluid dynamics (CMFD) models and to propose new closure laws. The presented research will demonstrate how the multiphase DNS data can inform the development of computational fluid dynamics (CFD) models. In particular, the Reynolds stress distribution will be evaluated for single- and two-phase bubbly flows and the level of turbulence anisotropy will be measured in several scenarios. The results will help determine if the isotropic turbulent models are suitable for bubbly flow applications or if there is a strong need to apply and develop Reynolds-stress turbulent models for two-phase flow CFD modeling.

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Figures

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Fig. 1

Bubble initial condition for one of the cases in a mesh study

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Fig. 2

Initial acceleration time to the domain outflow (bottom plot) and flow-through time of a single-bubble (top) as a function of the interface half-thickness (in terms of grid resolution)

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Fig. 3

The simulation domain dimensions and axis orientation. Walls are shown as shaded areas.

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Fig. 4

Hexahedral mesh used for the two-phase flow simulation of 60 bubbles in the moderate (400) Reynolds number flow case

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Fig. 5

Typical fully developed single-phase solution used to initialize the bubbly flow case

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Fig. 6

Initial distributions of 60 bubbles (a) set by the distance field initial condition for the moderate Reynolds number flow case. (b) Quality of the bubble representation by a hexahedral mesh.

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Fig. 7

Turbulent bubbly flow simulation at time step 8800. The instantaneous liquid velocity distribution is shown in planes with periodic boundary conditions and the bubble distribution is shown within the computational domain.

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Fig. 8

Turbulent bubbly flow simulation at time step 8800. Bubbles and 3D contours of the y-component of the velocity curl are shown.

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Fig. 9

Reynolds stress components obtained by the PHASTA code (symbols) compared to the results of Kim et al. (dashed lines) [27] for a Reynolds number of 180 based on the friction velocity. Here and in Figs. 10–15, the curve notation is as follows: top curve is stream-wise component (u), middle curve is span-wise component (w) and bottom curve represents normal-to-the-wall component (v).

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Fig. 10

Reynolds stress components obtained by the PHASTA code (symbols) compared to the results of Moser et al. (dashed lines) [26] for a Reynolds number of 400 based on the friction velocity

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Fig. 11

Anisotropy distribution for a single-phase turbulent flow, Reτ = 180 (dashed lines indicate the approximate values over the range of y+ 60–120)

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Fig. 12

Anisotropy distribution for a single-phase turbulent flow Reτ = 400 (dashed lines indicate the approximate values over the range of y+ 100–300)

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Fig. 13

Reynolds stress components obtained from the 1% void fraction two-phase flow computation (Reτ = 180) compared with the single-phase results of Moser et al. [26] (dashed lines)

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Fig. 14

Anisotropy distribution for a two-phase turbulent flow Reτ = 180 (the colored dashed lines indicate the approximate values over the range of y+ 60–140; the dash-dotted line shows the gas volume fraction distribution for the bubbly flow)

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Fig. 15

Anisotropy distribution for a two-phase turbulent flow Reτ = 400 (the colored dashed lines indicate the fitted values over the range of y+ 100–220; the dashed-dotted line shows the gas volume fraction distribution for the bubbly flow)

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