The exploration of multifunctional systems to harvest wave energy has become increasingly prominent in recent research. This paper presents a comprehensive investigation into the effectiveness of ...utilizing a wave energy converter (WEC) not only for energy generation but also as a coastal protection measure. Among the various types of WECs, the Oscillating Water Column (OWC) stands out as particularly promising due to its inherent advantages and notable efficiency. The versatility of the OWC allows for standalone installation or integration into hybrid systems, such as combining it with breakwaters. While numerous studies have examined the integration of OWCs with Caisson-type breakwaters, research on their integration with Semi-circular breakwaters (SCBW) is scarce. This study fills this gap by utilizing the open-source computational fluid dynamics (CFD) tool, OpenFOAM, to analyze the hydrodynamic performance of an OWC embedded within an SCBW. The numerical findings are validated against existing experimental data, enabling a thorough comparative analysis between the performance of an isolated OWC and a hybrid OWC integrated with SCBW. The investigation delves into various parameters, including wave amplification factor, chamber air and water pressure, external water pressure, energy transfer efficiency from chamber water to air, and wave run-up over the SCBW face. The results conclusively demonstrate that an OWC integrated with SCBW exhibits superior hydrodynamic performance compared to standalone configurations.
•Comparison of hydrodynamic performance of an isolated and hybrid OWC is investigated.•The effect of wavelength and wave steepness on the hydrodynamic performances of both OWC systems are reported.•Sloshing phenomena inside the OWC chamber are discussed.•Energy loss from chamber water to the air chamber has been investigated.•Effect of runup over the face of SCBW and the effects of the harbour wall on the efficiency of the OWC are also studied.
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.
Flash boiling is the sudden change from liquid to vapour phase and in IC engines it typically occurs during the injection process with a gasoline direct injection (GDI) setup and when high fuel ...temperatures result in saturation pressures higher than the in-cylinder ones. The flash boiling, due to the complex evolution of a multi-phase flow and a rapid droplet vaporisation, promotes spray atomisation and affects significantly the spray structure and fuel–air mixture formation, with consequences for the engine performance and pollutant emissions. Hence, a deep knowledge of such phenomenon is required to improve the combustion process and reduce the pollutant production. The breakup mechanism of a superheated spray is quite different from a regular one, because it features the nucleation and growth of bubbles within liquid droplets. In this paper, an innovative flash-boiling breakup model was embedded in a Eulerian–Lagrangian two-phase solver using OpenFOAM library. The model assigns to the droplets a radial velocity component due to the bubble explosion, making it capable of reconstructing the spray expansion. The code was tested using experimental data of the ECN Spray G injector covering various thermodynamic conditions. The numerical model achieves a good level of agreement with the experimental data and, in particular, it is able to reconstruct the spray collapse. Besides, it provides useful information regarding parameters that are intrinsically difficult to measure experimentally.
•ECN SprayG.•Flash-boiling atomisation.•OpenFOAM.•Breakup modelling.•Lagrangian spray.
Ensuring hydrogen safety has become of great significance nowadays, whose leakage can possible result in the deflagration to detonation (DDT). The numerical study aims to explore the effect of solid ...obstacle distribution on the DDT in a homogeneous hydrogen-air mixture. Results show that the detonation initiation process can be classified into two types: i) local spherical detonation caused by the coupling of flame surface and high-pressure region; ii) detonation triggered by the interaction between the upper wall and multiple compression waves in front of the flame. Also, this study finds that the flame acceleration (FA) experiences two periodic “acceleration-deceleration” processes before the detonation initiation, and the initiation distance and time are the shortest when the obstacles are symmetrically distributed. Further, the higher the unilateral blockage ratio, the more unfavorable DDT occurs. The present results highlight the effect of different solid obstacle distribution patterns on the FA and DDT process.
•Different obstacle distribution patterns affect the flame acceleration process.•Two different detonation initiation processes are classified.•Flame velocity undergoes periodic “acceleration-deceleration” processes.•Symmetrical distribution of obstacles is most conducive to DDT.•Location and time of detonation initiation vary with the obstacle distribution.
•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.
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 %.
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.
We devise a numerical method for passive advection of a surface, such as the interface between two incompressible fluids, across a computational mesh. The method is called isoAdvector, and is ...developed for general meshes consisting of arbitrary polyhedral cells. The algorithm is based on the volume of fluid (VOF) idea of calculating the volume of one of the fluids transported across the mesh faces during a time step. The novelty of the isoAdvector concept consists of two parts. First, we exploit an isosurface concept for modelling the interface inside cells in a geometric surface reconstruction step. Second, from the reconstructed surface, we model the motion of the face–interface intersection line for a general polygonal face to obtain the time evolution within a time step of the submerged face area. Integrating this submerged area over the time step leads to an accurate estimate for the total volume of fluid transported across the face. The method was tested on simple two-dimensional and three-dimensional interface advection problems on both structured and unstructured meshes. The results are very satisfactory in terms of volume conservation, boundedness, surface sharpness and efficiency. The isoAdvector method was implemented as an OpenFOAM® extension and is published as open source.
•CFD simulation of CO2 methanation in a shell-and-tube reactor was performed.•A conjugated heat transfer solver was developed using OpenFOAM.•The VOF model was implemented for phase change of the ...water on the shell side.•A large catalyst heat conductivity facilitates heat transfer to the shell side.•Using boiling water can effectively reduce the coolant flow rate.
This paper reports a computational fluid dynamics simulation of carbon dioxide (CO2) methanation via the Sabatier process in a shell-and-tube reactor, incorporating a water phase change simulation on the shell side using the volume of fluid (VOF) method. The essential heat removal factors and their mechanisms, such as the catalyst size, bed porosity, thermal conductivity, coolant flow rate, and coolant boiling, were primarily investigated. The computational code was a newly developed in-house version of ChtMultiRegionFOAM based on OpenFOAM v2006. This code can simulate catalyst-gas heat transfer, which is called the two-temperature model. The code was extended to new methanation and phase-change models based on the VOF method. The computational code was first validated using existing experimental data. After sufficient accuracy was confirmed, several parametric studies were conducted. Catalyst heat conductivity was the most influential factor among the catalyst-related parameters. The flow rate of the oil coolant significantly affected the cooling performance. Finally, the use of boiling water significantly reduced the coolant flow rate. Moreover, the cooling performance remained unchanged until the total heat release rate from the gas exceeded the total latent heat of the water.
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