1www.nugenia.org www.snetp.eu

www.nugenia.org

NUGENIA is mandated by SNETP to coordinate

nuclear Generation II & III R&D

Project SPH-2PHASEFLOW

Simulation of two-phase flow patterns

with a new approach based on

Smoothed Particle Hydrodynamics

Jean-Pierre Minier

(EDF R&D)

This project has received funding from the Euratom Seventh Framework Programme under grant agreement No 604965.

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Contents

General context and purpose of the project

Two-phase flow patterns and regime maps

Choice of the numerical approach

Organisation and specific aims of the project

Overview of basic features of SPH

Results obtained during the project

Validation in “elementary test cases”

Applications for two-phase flow regimes

Assessment with respect to other methods

Conclusion

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Two-phase flow issues in

Nuclear Power Plants (NPP)

Analysis of re-floods of damaged reactors

in severe accident scenarios

Study of steam-generator operating

conditions (also connected to tube fouling

and tube-support-plate particle clogging)

Fragmentation of vapour pockets in pumps

Formation of liquid films along walls, in

turbines and in severe accident scenarios

The well-known boiling (or heat flux) crisis

Particle deposition in two-phase flows

(AOA, steam-generators, etc.)

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Two-phase flow patterns

Various topologies of the liquid-gas

interface create a range of “flow patterns”

These “regimes” depend on the

orientation, fluid properties, operating

conditions…and on many unknowns!

Capturing regime transitions is an open issue

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Flow maps in vertical pipes

Existing regimes are often predicted from

empirical flow maps (for each situation!)

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Different flow maps can exist

These maps are qualitative (“observation”)

Extrapolation to other conditions is risky

Need for numerical approaches to try to

predict changes in two-phase flow patterns

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Which numerical approach?

Three levels of description can be used

The component-level of description

A local but statistically-average 3D

description based on “two-fluid models”

A local and instantaneous 3D level based

on Direct Numerical Simulation (DNS)

It is essential to be aware of the range of

validity of each level of description

Two-fluid models yield only one-point

information and it is NOT POSSIBLE to

capture two-phase flow regime transitions

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A classical pitfall…

One-point information on local values of the

gas and liquid volume fractions do not give

access to two-point information!

Illustration with a simple situation:

One-point values of 𝜶𝒍 𝒕, 𝒙 and 𝜶𝒈 𝒕, 𝒙 can

be exact but coalescence cannot be

predicted based on that sole information!

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Choosing the numerical model

To capture changes in two-phase flow

patterns, a DNS-like approach is needed

Both separated and dispersed regimes must

be handled properly in a single formulation

Selection of a new numerical approach

departing from traditional formulations

A particle-based approach:

Smoothed Particle Hydrodynamics (SPH)

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Aim of the project

SPH is increasingly used for single-phase

flows and, especially, free-surface flows

However, for two-phase flow applications,

the SPH method is still in its infancy

The overall objective of the NUGENIA

project is to assess the interest and the

potential of the SPH formulation for critical

two-phase flow problems

This approach is not meant to replace

more macroscopic formulations but to

complement them for specific issues

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Specific objectives

Development of a two-phase SPH model

for water/vapour two-phase flows

Assessment of the ability of the “two-phase

SPH” formulation to capture changes in

two-phase flow patterns

Analysis of specific cases (either specific

physical phenomena and/or mixed

separated/dispersed flow situations)

A step-by-step approach to be understood in

a long-term perspective

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Organisation of the project

Three partners are involved:

Electricité de France, Research Division,

Department for Fluid Dynamics, Power

Generation and Environment (EDF R&D)

Institute of Fluid Flow Machinery, Polish

Academy of Sciences, Gdansk, Group of

Multiphase Flows (IMP Gdansk)

Università degli Studi di Udine, Department

of Electrical, Management and Mechanical

Engineering, Multiphase Flow (Univ. Udine)

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What is SPH? Some basics

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Governing equations

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Accounting for surface tension

surface tension at the interface represented as

volume force ("continuum surface force",CSF)

[Brackbill et al., JCP 1992]:

SPH of liquid jet breakup[Wawreńczuk, 2004]

the normal unit vector based on

phase indicator ("color function "c)

and the interface curvature:

in the simplest SPH setting:

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Validation for simple cases

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Rayleigh-Plateau instability

SPH 2D/3D simulation of liquid column break-up (movies)

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two rising bubbles (side setting)

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Droplet/bubble deformation

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Droplet/bubble deformation

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Interfacial area density

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Numerical setup

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Results – slug flow

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Results – annular flow

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Results – churn flow

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Results – regime map

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Results – regime transition

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First test on mixed

separated/dispersed flows

Study of liquid film dynamics with droplet

separation and re-entrainment

Work in the last months was focused on

assessing SPH with respect to the Phase

Field Method developed at Univ. Udine)

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Feedback on the project

Six technical meetings between the three

partners in 2015-2016

Three technical reports

“Report on the definition of the benchmark

case” (D1: 09/2015)

“Report on the formulation of the two-phase

SPH method and applications to the

predictions of two-phase flow patterns”

(D2-M1: 01/2016)

“Report on the assessment of the two-phase

SPH approach” (D3-M2: 09/2016)

Presentations in International Conferences

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Conclusions

Even in the short time-span of the project,

interesting results have been obtained

A new “2phase SPH” formulations has been

developed and validated

Numerical results demonstrate the

potential and the interest of SPH for

complex issues of two-phase flows

The ability of SPH to capture changes of

two-phase flow regime is confirmed

However, this is not a “ready-to-be-blindly-

used method” and present results should

be the basis of longer-term projects

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Thank you for your attention

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www.nugenia.org

NUGENIA is mandated by SNETP to coordinate

nuclear Generation II & III R&D