LEIS for the prediction of turbulent multifluid flows applied to thermal-hydraulics applications
Introduction
The computational thermal-hydraulics scene has gone through successive transitions, motivated by new needs and developments. The first real transition triggered in the 1980s focused on removing gradually the limitations of lumped-parameter 1D modelling by further developing the two-fluid model for 3D turbulent flow problems (Ishii, 1975). This is now the state-of-the-art. The advent of the so-called interface tracking methods (ITM) in the late 80s (Kataoka, 1986), which permit to better predict the shape of interfaces while minimizing the modelling assumptions for momentum interaction mechanisms, has somewhat shifted the interest towards a new transition. The most recent transition is now underway: it specifically centres on the use of these new simulation techniques (ITM) for practical thermal-hydraulics cases, after it has been validated for canonical two-phase flow problems, including bubble rise, drop splashing or bouncing, stratified air–water flows, and many other examples (Lemonnier et al., 2005). But this latest transition poses interesting challenges to the computational thermal-hydraulics community, and raises some specific questions: how to migrate from averaged two-fluid formulation modelling to more refined interface tracking prediction (or combine them when necessary), and from steady-state Reynolds averaged modelling to unsteady large-scale turbulence simulation. The transition is not a matter of availability of computational power and resources only, but a question of adequacy of code algorithmic (precision), complex meshing, and proper modelling of the underlying flow physics, both in the core and near the interfaces. Some recent developments in this area were reviewed by Yadigaroglu and Lakehal (2005) with emphasis on both single- and multiphase thermal-hydraulics.
This paper is written in that spirit, focusing on a new concept that combines the strength of these ITM methods with the advantage of unsteady, large-scale prediction of turbulence, known as the Large-Eddy Simulation (LES). The outcome of this combination is a better way to capture transients of interfaces and associated turbulence, while minimizing modelling (of both: turbulence and interface dynamics). This is the reason why we refer to this approach as LEIS: solving in time as much interface and turbulence scales as possible. We will here limit the mathematical derivations; instead, we will focus on premises, difficulties and required future developments.
Section snippets
Nature and forms
Multiphase flows appear under various forms depending on the nature of the involved fluids and their rate of presence in the system. A fluid–fluid system may be defined as a “diffuse mixed flow” if the transported phase is rather dilute in the carrier phase, the density ratio between the phases is rather small (<10–15%), e.g. meaning that the fluids do not exert substantial momentum exchange on each other, allowing the transported phase to diffuse into the carrier media by molecular and
Dealing with interfacial scales (IS)
Interfacial flows refer to two-phase flow problems involving two or more immiscible fluids separated by sharp interfaces which evolve in time. Typically, when the fluid on one side of the interface is a gas that exerts shear (tangential) stress upon the interface, the latter is referred to as a free surface. Interface tracking/capturing schemes are methods that are able to locate the interface, not by following the interface in a Lagrangian sense (e.g. by following marker points residing on the
TransAT© multiphase flow software
The CMFD code TransAT© developed at ASCOMP is a multi-physics, finite-volume code based on solving multifluid Navier–Stokes equations. The code uses structured meshes, though allowing for multiple blocks to be set together. MPI parallel based algorithm is used in connection with multi-blocking. The grid arrangement is collocated and can thus handle more easily curvilinear skewed grids. The solver is pressure based (Projection Type), corrected using the Karki–Patankar technique for low-Mach
Validation
The stratified air–water flow of Fulgosi et al. (2003) is the appropriate validation case for SGS modelling, since a complete DNS database is available for comparison, and because the flow does not feature interface fragmentation that would have complicated the analysis. Here we compare model (9–10) with the DNS data, the under-resolved DNS without SGS modelling. The comparison includes the results of the VMS approach of Hughes et al. (2001), in which in contrast to filtering the equations are
Slug formation in circular pipes
This test case considered here consists of a co-current stratified two-phase flow containing gas and liquid ammonia (Martin, 2005) injected at various gas and liquid superficial velocities and inflow void fractions. Specifically we discuss here the results of the ‘turbulent case’ with superficial gas velocity of 14 m/s, superficial liquid velocity of 0.5 m/s; and void fraction 50% (i.e. where the pipe is simply half filled). The pipe length is 6.3 m, and the diameter is 0.14 m. The ‘laminar case’
Concluding remarks and future developments
The paper aimed at describing the way computational thermal-hydraulics is migrating to more sophisticated modelling techniques, transcending the two-fluid formulation and steady-state RANS equations for turbulence by integrating ITM's within the LES framework, defined here as “LEIS”. The case studies outlined in this paper illustrate what can be done with LEIS for a class of turbulent interfacial two-phase flows. The method can be successfully applied to generate realistic transient simulations
Acknowledgements
The theoretical part of the work mentioned here was initiated at ETH-Zurich under the supervision of Prof. George Yadigaroglu, more precisely at the CMFD group (Dr. P. Liovic, Dr. M. Fulgosi, Dr. C. Narayanan, Dr. S. Reboux). The new simulations shown here were conducted using the TransAT code of ASCOMP by Daniel Caviezel and “Chidu” Narayanan, partially within NURESIM, An EC-funded project in the framework of the Sixth EURATOM Framework Program (2004–2006). CEA has kindly provided the COSI
References (31)
Local instant formulation of two-phase flow
Int. J. Multiphase Flow
(1986)- et al.
Towards Large Eddy simulation of isothermal two-phase flows: governing equations and a priori tests
J. Multiphase Flow
(2007) - et al.
Interface tracking towards the direct simulation of heat and mass transfer in multiphase flows
Int. J. Heat Fluid Flow
(2002) - et al.
A three-dimensional unsplit-advection volume tracking with planarity-preserving interface reconstruction
Computers & Fluids
(2006) - et al.
Interface–turbulence interactions in large-scale bubbling processes
Int. J. Heat Fluid Flow
(2007) - et al.
Multi-Physics treatment in the vicinity of arbitrarily deformable fluid–fluid interfaces
J. Comp. Phys.
(2007) Computational simulation of multi-D liquid–vapor thermal shock with condensation
- et al.
The motion of a large gas bubble rising through liquid flowing in a tube
J. Fluid Mech.
(1978) - et al.
Direct numerical simulation of turbulence in a sheared air–water flow with a deformable interface
J. Fluid Mech.
(2003) - et al.
Monotonically integrated LES of free shear flows
AIAA Journal
(1999)
A dynamic sub-grid-scale eddy viscosity model
Phys. Fluids
Volume of fluid (VOF) method for the dynamics of free boundaries
J. Comp. Phys.
LES of turbulent channel flows by the variational multiscale method
Phys. Fluids
Thermo-fluid Dynamics Theory of Two-Phase Flow
On the modelling of multiphase turbulent flows for environmental & hydrodynamics applications
Int. J. Multiphase Flow
Cited by (32)
Large-eddy simulation of droplet-laden decaying isotropic turbulence using artificial neural networks
2021, International Journal of Multiphase FlowPlanar jet stripping of liquid coatings: Numerical studies
2020, International Journal of Multiphase FlowCitation Excerpt :Then, dynamic grid refinement will act as usual, the only difference being that refinement to the maximum level will take place only in chosen domain sub-areas while outside of them a lower maximum level is forced. This tactic of refinement situates the presented simulation between the block-based (Lakehal, 2010) and point-based (Popinet, 2009) mesh refinement. Its drawback is the increase in the globally calculated numerical dissipation.
Near-interface flow modeling in large-eddy simulation of two-phase turbulence
2020, International Journal of Multiphase FlowInvestigation on turbulence in the vicinity of liquid-liquid interfaces – Large eddy simulation and PIV experiment
2019, Chemical Engineering ScienceCitation Excerpt :Several studies have adopted LES for modelling interfacial flows with industrial applications in the past and ongoing literature. A couple of examples include large eddy simulation of plunging breaking waves (Lubin et al., 2006), gas-jet wiping process (Lacanette et al., 2006), turbulent bubbling process (Liovic and Lakehal, 2007), multiphase thermal-hydraulics (Lakehal, 2010) and two-phase flow in heat exchangers of nuclear power plants (Mimouni et al., 2017). In the application of interfacial LES in metallurgical flows, a series of work has been published on the multiphase flow in continuous casting process (Sulasalmi et al., 2009; Liu et al., 2013; Huang et al., 2015).
New turbulence modeling for simulation of Direct Contact Condensation in two-phase pressurized thermal shock
2018, Progress in Nuclear Energy