The Lead-bismuth cooled Fast Reactors (LFR) utilizes wrapped hexagonal fuel assemblies arranged in a honeycomb pattern. The inter-wrapper flow (IWF) between adjacent assemblies has a significant ...influence on the core thermal-hydraulics. In this paper, the LFR core assembly analysis model, inter-wrapper flow and heat transfer model, and multi-scale coupling analysis model were developed and were implemented into the previously self-developed subchannel-level three-dimensional thermal hydraulic analysis code CorTAF-LBE for whole core of LFR, which is based on the OpenFOAM computational fluid dynamics simulation platform. The inter-wrapper flow and heat transfer model was validated against the KALLA-IWF experiment. Whole core steady state operating condition and low flow rate condition simulations were performed with reference to the 19-rod bundle geometry from KALLA laboratory and typical LFR core assembly arrangement. The whole core steady state distribution laws of key thermal-hydraulic parameters were obtained, and the influence of low flow rate operation on safety parameters such as cladding and pellet temperatures was analyzed. Under low flow rate operating conditions, the IWF heat transfer was accounted for 4.87% of the core thermal power, which was 315.6 kW higher than that under normal operating conditions, playing an important role in core heat removal and safe operation. This work provides important insights into LFR core design and the assessment of the role of IWF under low flow rate conditions.
•The Multi-scale coupling analysis model is established and implanted into the CorTAF-LBE code.•The steady-state thermal-hydraulic parameter distribution at whole core scales is analyzed.•The effect of inter-wrapper flow on core heat transfer at low flow rate condition is evaluated.
In this work, the performance of a buoyancy-modified turbulence model is shown for simulating wave breaking in a numerical wave flume. Reynolds-Averaged Navier-Stokes (RANS) modelling is performed by ...applying both a k-ω and a k-ω SST turbulence model using the Computational Fluid Dynamics (CFD) toolbox OpenFOAM. In previous work of the authors (Devolder et al., 2017), the observed significant decrease in wave height over the length of the numerical wave flume based on RANS turbulence modelling for the case of propagating waves has been avoided by developing a buoyancy-modified k-ω SST model in which (i) the density is explicitly included in the turbulence transport equations and (ii) a buoyancy term is added to the turbulent kinetic energy (TKE) equation. In this paper, two buoyancy-modified turbulence models are applied for the case of wave breaking simulations: k-ω and k-ω SST. Numerical results of wave breaking under regular waves are validated with experimental data measured in a wave flume by Ting and Kirby (1994). The numerical results show a good agreement with the experimental measurements for the surface elevations, undertow profiles of the horizontal velocity and turbulent kinetic energy profiles. Moreover, the underlying motivations for the concept of a buoyancy-modified turbulence model are demonstrated by the numerical results and confirmed by the experimental observations. Firstly, the buoyancy term forces the solution of the flow field near the free water surface to a laminar solution in case of wave propagation. Secondly in the surf zone where waves break, the buoyancy term goes to zero and a fully turbulent solution of the flow field is calculated. Finally and most importantly, the buoyancy-modified turbulence models significantly reduce the common overestimation of TKE in the flow field.
•Simulations of wave breaking in a numerical wave flume using OpenFOAM®.•Performance of a buoyancy-modified k-ω and k-ω SST turbulence model are evaluated.•The buoyancy-modified turbulence models are validated with experimental results.•Accurate predictions of the turbulent flow field at the wave breaking zone.
We monitor the evaporation of a volatile liquid (ethanol) from an inkjet-printed liquid film, consisting of a mixture of ethanol and ethylene glycol. Interferometric video imaging technology is used ...for recording 2D vapor concentration profiles over the evaporating film. The vapor flow is reconstructed using numerical simulations. In this way, we reconstruct the complete flow velocity profile, and distinguish diffusive and convective gas transport, with quantitative tracking of the transport balances. The convective flows are driven by the buoyancy of the solvent vapor in the ambient air. In particular, we reconstruct the evaporation process from the interface of the two-component liquid. We monitor the evaporation flows, implement Raoult’s and Henry’s laws of vapor pressure reduction, as well as evaporation resistivity. We observe the edge-enhancement of evaporation flows at the wetting rims of the liquid film, and decompose the vapor flows in the diffusive and the convective contribution. We demonstrate how Langmuir’s evaporation resistivity can be identified using vapor pressure profiles in the gas phase data and mass transfer balances.
•Mass transfer resistance due to surfactants explains reduced evaporation rates.•Enhancement of evaporation at the contact line reproduced in numerical simulation.•Quantitative separation of diffusive and convective vapor flux using CFD.
Liquid Metal Batteries (LMBs) are a promising concept for cheap electrical energy storage at grid level. These are built as a stable density stratification of three liquid layers, with two liquid ...metals separated by a molten salt. In order to ensure a safe and efficient operation, the understanding of transport phenomena in LMBs is essential. With this motivation we study thermal convection induced by internal heat generation. We consider the electrochemical nature of the cell in order to define the heat balance and the operating parameters. Moreover we develop a simple 1D heat conduction model as well as a fully 3D thermo-fluid dynamics model. The latter is implemented in the CFD library OpenFOAM, extending the volume of fluid solver, and validated against a pseudo-spectral code. Both models are used to study a rectangular 10×10 cm² Li||Bi LMB cell at three different states of charge.
Coupled multi-physics simulations play a crucial role in the design and operation of nuclear reactors, particularly in assessing the behavior of used nuclear fuel. This study focuses on exploring the ...efficacy of coupled calculations for used nuclear fuel through the integration of neutron transport and thermal-hydraulics codes. Neutronics calculations were conducted using the Monte Carlo code Serpent, while thermal-hydraulic calculations utilized the Computational Fluid Dynamics (CFD) software OpenFOAM. The investigation was focused on a VVER-440 fuel pin situated in a hexagonal coolant flow area. Three computational grids were generated, containing 0.15 million, 0.39 million, and 1.1 million computational cells, along with three variants of axial material refinement featuring 42, 21, and 10 material layers. The purpose was to analyze the impact of spatial refinement on key parameters such as multiplication factor, power flux, and temperature fields. Several relaxation factors in Picard iterations were systematically compared to enhance the convergence speed of the coupling procedure. Notably, simulations without relaxation (α = 1) resulted in oscillations in predicted results, while a low value of α led to slow convergence. The investigation revealed that employing a stochastic approximation with a varying relaxation factor coupled with a varying number of simulated particles demonstrated superior performance compared to cases with a constant relaxation factor α or a stochastic approximation with a constant number of simulated particles. Furthermore, it was observed that the resolution of axial fuel segmentation significantly influenced predicted multiplication factor kinf and temperature profiles. Interestingly, the spatial resolution of the computational grid exhibited minimal impact on the predicted results.
•CFD code OpenFOAM and Monte Carlo neutron transport code Serpent were coupled.•Relaxation of power flux improved the simulation convergence.•The stochastic approximation converged faster than the fixed number of neutrons case.•Axial segmentation of material input had a significant effect on predicted results.
A multi-species cavitation model is applied to a high-pressure injection cycle. Results of transient simulations with ballistic needle dynamics are presented. Species segregation in terms of local ...species demixing in the liquid phase is assessed. Therefore, the mass transfer cavitation model proposed by 101 is adopted and implemented in an incompressible large-eddy simulation flow solver. The model is based on the Rayleigh bubble dynamics equation, Raoult's and Dalton's law, vapor-liquid equilibrium, and mixing rules. It is initially tested on a hydrofoil test case and subsequently applied to a high-pressure injector. A heavier n-dodecane/n-heptane and a lighter n-octane/n-heptane mixture are considered. For both mixtures, essentially the same vortex and vapor structures are encountered. No distinct hysteresis between opening and closing phase of the cycle is present, which is related to a relatively low liquid density of both mixtures. Segregation correlates with the amount of vapor and is most pronounced for cloud cavitation at low needle lift levels and minor for string cavitation at high needle lift levels. It is considerably more pronounced for the heavier than the lighter mixture due to a wide spread of volatilities of n-dodecane and n-heptane. Even for the heavier mixture, segregation is much less pronounced than observed in the immediate environment of a single bubble. This observation is related to the homogeneous mixture approach, by which an averaged effect of segregation over the computational cell is assumed. An Euler-Lagrange approach is proposed for future studies, embedding details of mass transfer over the bubble interface into the CFD code.
•A multi-species cavitation model for 3D simulations is presented.•Two-species simulation results for ballistic needle dynamics are presented.•A distinct hysteresis of vortex and vapor structures is absent.•Local mixture segregation occurs at low needle lift.•Higher segregation for heavier than for lighter mixture occurs.
•We developed an open-source workflow to characterize open-cell solid foams.•The geometry generation is performed by using the computer graphics code Blender.•Fluid flow and mass transfer are ...simulated using open-source CFD code OpenFOAM.•From the CFD results permeability and filtration rate are calculated.•The workflow (available online) is used to investigate a large number of different foams.
Open-cell foams are porous materials characterized by high porosity and large specific surface, industrially employed as catalyst supports or particulate filters. These materials can be modelled using periodic lattices, or with more complex approaches based on Voronoi tessellations. This work introduces, tests, and makes available an open-source workflow (Agostini, 2021) based on Blender that can reproduce great varieties of geometries with a limited cost for their modeling. An example of the exploration capabilities of this workflow is presented in the form of CFD simulations for flow field and mass transfer (performed with OpenFOAM) on the created geometries, eventually obtaining an effective particle deposition/filtration coefficient Kd. The results are interpreted using constitutive equations and other functional forms depending on geometric parameters which prove to be insufficient in explaining the variations in filtration performance, highlighting the need for more detailed exploration, the objective for which this workflow was developed.
Liquid Metal Batteries (LMBs) are a promising grid-scale energy storage technology that offers low costs per kilowatt-hour, high energy and current densities, as well as low fade rates. The ...all-liquid composition of the batteries, as well as the presence of temperature gradients and electric and magnetic fields, result in the occurrence of multiple fluid phenomena. These can affect the hydrodynamic stability of the battery, thereby making their interactions critical to understand. In this work, the interaction of Rayleigh-Bénard convection and Electro-vortex flow is investigated as these types of flow will be present in Liquid Metal Batteries from laboratory to grid-scale. A single-layer electrode is simulated, and the computed results compared with experimental data from the literature. It was found that Rayleigh-Bénard convection is unsteady in the liquid metal electrode. The introduction of a 2 A current stabilises the convection cells, whilst the introduction of a 40 A current leads to the dominance of Electro-vortex flow at the central region of the electrode. The results in this work match experimental data closer than previously published models offering insight into the interaction between Rayleigh-Bénard convection and Electro-vortex flow in the anodes of discharging Liquid Metal Batteries.
•Development of a numerical model for Liquid Metal Batteries.•Coupled model of Rayleigh-Bénard convection and Electro-vortex flow.•At high currents, electro-vortex flow dominates under the current collector.•At low currents, Rayleigh-Bénard convection is stabilised by induction.
Green infrastructure can reduce PM2.5 traffic emissions on a city scale, by a combination of dispersion by trees and deposition on buildings, trees and grass. Simulations of PM2.5 concentrations were ...performed using a validated CFD model. A 2 × 2 km area has been reconstructed as a 3D representation of Leicester (UK) city centre which is on a scale larger than most of the other CFD studies. Combining both the effects of tree aerodynamics and the deposition capabilities of trees and grass is also something that has not yet been modelled at this scale. During summer time in Leicester City, the results show that the aerodynamic dispersive effect of trees on PM2.5 concentrations result in a 9.0% reduction. In contrast, a decrease of PM2.5, by 2.8% owing to deposition on trees (11.8 t year−1) and 0.6% owing to deposition on grass (2.5 t year−1), was also observed. Trees and grass are shown to have greater effects locally, as smaller decreases in PM2.5 were found when considering reduction across the whole boundary layer. Densely built areas like Leicester City centre have relatively less vegetation and subsequently have a smaller effect on PM2.5 concentration. It was found that particle deposition on buildings was negligible with less than 0.03%. An empirical equation was derived to describe the changes in PM2.5 based on ground surface fraction of trees and grass, and their deposition velocities.
•We model the effectiveness of trees and grass on traffic PM2.5 reduction.•City scale CFD simulations were performed under the OpenFOAM software.•Aerodynamics effect of tree prevails over deposition.•Tree are beneficial for wind speeds greater than 2 m s−1.•PM2.5 deposition on buildings is negligible with less than 0.03 %.
•Unsteady sheet/cloud cavitating flows are studied using the compressible cavitation solver developed on OpenFOAM.•Cavitation fluid compressibility effects on transient flow structures and dynamics ...are illustrated.•Effects of density variance on velocity divergence are proposed.•The physics for the compressibility effects on cavitation vortex dynamics are investigated based on VTE budget analysis.
The objective of the paper is to investigate the physics involved in the compressible cavitating flows, with emphasis on the compressibility effects. 3-D numerical simulations were conducted on the open source software platform OpenFOAM, using both the native incompressible cavitation solver interPhaseChangeFOAM and implemented compressible cavitation solver, where the cavitation model and turbulence model are kept the same and differences of the two approaches mainly root in the density variances of pure liquid and pure vapor. Results are presented for the transient sheet/cloud cavitating flows around a Clark-Y hydrofoil fixed at attack of angle α=8° at inlet velocity U=10m/s and cavitation number σ=0.8, where both ensemble averaged statistics and transient characteristics are analyzed. Good agreement can be obtained using both the incompressible and compressible approaches when compared with the experiment data. While it is found that compared with the incompressible approach, the compressible approach can predict the unsteady cavitation evolution and cavity shedding frequency better. With the compressibility effects considered, the time averaged void fraction distribution decreases, and the cavity size (i.e. cavitation area) becomes smaller. The re-entrant flow thickness normalized by local cavity thickness predicted by the compressible approach is larger than that by the incompressible approach, indicating that the compressible approach can predict the re-entrant jet dynamics well. The velocity divergence analysis show that compared with that in incompressible approach, where velocity divergence mainly comes from the mass transfer between phases, in compressible approach, the velocity divergence originates from both the cavitation two-phase fluid compressibility and mass transfer, and the fluid density variance dominates in compressible results. Following, the budget analysis of vorticity transport equation (VTE) show that the vortex stretching term dominates the cavitation vortex dynamics. Compressibility effects will significantly increase the dilatation term and decrease baroclinic term by decreasing the misalignment between density gradient and pressure gradient. Finally, the temperature and density variance in different cavitation structures are presented.
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