The simulation of heat pipe microreactors is an active area of research. In this paper, a thermal analysis of a heat pipe microreactor motivated by the eVinci™ design is performed. Thorough ...discussion on the modeling of heat pipes without a dedicated heat pipe modeling code, such as Sockeye, is also provided. The performance of two heat pipe modeling techniques is compared, one a more accurate approach which explicitly tracks heat pipe temperatures, and the other an approximation which simplifies the thermal hydraulic model development. One-way coupling is used where the Serpent neutronics code is used to generate a power distribution which is applied in an OpenFOAM model to calculate a temperature distribution. After a detailed convergence analysis, the core temperature distribution resulting from a core with control drums facing outward, or fully withdrawn, is compared with one having the control drums facing inward, or fully inserted. Finally, a parametric analysis was performed where the thermal resistances associated with the heat pipe model were varied and core temperatures were tracked. It was observed that the relationship between average and maximum core temperatures had a highly linear relationship to the thermal resistances used in the heat pipe model.
•OpenFOAM performs thermal simulations on an eVinci-like microreactor.•Serpent code generates power distribution; OpenFOAM calculates temperature.•A simplified heat pipe model based on a thermal resistance network is used.•Different iterative procedures for solving temperatures are explored.
The Reynolds-averaged Navier–Stokes (RANS) equations provide a computationally efficient method for solving fluid flow problems in engineering applications. However, the use of closure models to ...represent turbulence effects can reduce their accuracy. To address this issue, recent research has explored data-driven techniques such as data assimilation and machine learning.
An efficient variational data assimilation (DA) approach is presented to enhance steady-state eddy viscosity based RANS simulations. To account for model deficiencies, a corrective force term is introduced in the momentum equation. In the case of only velocity reference data, this term can be represented by a potential field and is divergence-free. The DA implementation relies on the discrete adjoint method and approximations for efficient gradient evaluation.
The implementation is based on a two-dimensional coupled RANS solver in OpenFOAM, which is extended to allow the computation of the adjoint velocity and pressure as well as the adjoint gradient. A gradient-based optimizer is used to minimize the difference between the simulation results and the reference data. To evaluate this approach, it is compared with alternative data assimilation methods for canonical stationary two-dimensional turbulent flow problems. For the data assimilation, sparsely distributed reference data from averaged high-fidelity simulation results are used.
The results suggest that the proposed method achieves the optimization goal more efficiently compared to applying data assimilation for obtaining the eddy viscosity, or a field modifying the eddy viscosity, directly. The method works well for different reference data configurations and runs efficiently by leveraging coarse meshes.
The objective of the present work is to investigate wave run-up around a monopile subjected to regular waves inside a numerical wave flume using the Computational Fluid Dynamics (CFD) toolbox ...OpenFOAM®. Reynolds-Averaged Navier-Stokes (RANS) turbulence modelling is performed by applying the k-ω SST model. Boundary conditions for wave generation and absorption are adopted from the IHFOAM toolbox. Simulations of propagating water waves show sometimes excessive wave damping (i.e. a significant decrease in wave height over the length of the numerical wave flume) based on RANS turbulence modelling. This anomaly is prevented by implementing a buoyancy term in the turbulent kinetic energy equation. The additional term suppresses the turbulence level at the interface between water and air. The proposed buoyancy-modified k-ω SST turbulence model results in an overall stable wave propagation model without significant wave damping over the length of the flume. Firstly, the necessity of a buoyancy-modified k-ω SST turbulence model is demonstrated for the case of propagating water waves in an empty wave flume. Secondly, numerical results of wave run-up around a monopile under regular waves using the buoyancy-modified k-ω SST turbulence model are validated by using experimental data measured in a wave flume by De Vos et al. (2007). Furthermore, time-dependent high spatial resolutions of the numerically obtained wave run-up around the monopile are presented. These results are in line with the experimental data and available analytical formulations.
•Simulations of wave run-up around a monopile in a wave flume using OpenFOAM®.•RANS turbulence modelling causes wave damping over the length of the flume.•A buoyancy-modified k-ω SST turbulence model is proposed to avoid wave damping.•The buoyancy-modified turbulence model is validated with experimental results.
In recent years OpenFOAM studies have focused on pure wave modelling and wave-structure interaction. Considering that there is a lack of transparency concerning effects of different motion modelling ...settings in OpenFOAM, this paper presents the influence of different numerical setups on the accurate modelling of wave-induced motions. This is achieved by applying the interFoam solver included in OpenFOAM-v2206 with the waves2Foam toolbox. The optimal numerical setup is studied with a two-dimensional box-like ship idealisation heaving in varying wave lengths while the wave steepness remains constant. Different numerical setups are considered for accurate wave modelling, the modelling of wave excitation forces for the case of a static structure, and heave motion modelling. Finally, the optimal setup that is found is applied for a 3D ship case in head waves with heave and pitch coupling. As far as practically possible, the results are validated against experimental data. It is shown that strict requirements for mesh density and time step for accurate wave modelling result in accurate excitation force and motion results. Reflections from the relaxation zones and different mesh density layers cause inaccuracies. It is concluded that simple numerical cases are suitable for studying optimal numerical setups for more complex simulation cases.
•Ten cells per wave height and an aspect ratio of four are accurate for wave modelling.•k−ω SST turbulence modelling is problematic in model-scale waves.•An upwind divergence scheme stabilises force and motion modelling results.•The dense resolution needed for wave modelling is accurate for wave structure studies.•Optimal numerical setups for complex cases can be studied with simple 2D cases.
dsmcFoam+ is a direct simulation Monte Carlo (DSMC) solver for rarefied gas dynamics, implemented within the OpenFOAM software framework, and parallelised with MPI. It is open-source and released ...under the GNU General Public License in a publicly available software repository that includes detailed documentation and tutorial DSMC gas flow cases. This release of the code includes many features not found in standard dsmcFoam, such as molecular vibrational and electronic energy modes, chemical reactions, and subsonic pressure boundary conditions. Since dsmcFoam+ is designed entirely within OpenFOAM’s C++ object-oriented framework, it benefits from a number of key features: the code emphasises extensibility and flexibility so it is aimed first and foremost as a research tool for DSMC, allowing new models and test cases to be developed and tested rapidly. All DSMC cases are as straightforward as setting up any standard OpenFOAM case, as dsmcFoam+ relies upon the standard OpenFOAM dictionary based directory structure. This ensures that useful pre- and post-processing capabilities provided by OpenFOAM remain available even though the fully Lagrangian nature of a DSMC simulation is not typical of most OpenFOAM applications. We show that dsmcFoam+ compares well to other well-known DSMC codes and to analytical solutions in terms of benchmark results.
Program title: dsmcFoam+
Program Files doi:http://dx.doi.org/10.17632/7b4xkpx43b.1
Licensing provisions: GNU General Public License 3 (GPL)
Programming language: C++
Nature of problem: dsmcFoam+ has been developed to help investigate rarefied gas flow problems using the direct simulation Monte Carlo (DSMC) method. It provides an easily extended, parallelised, DSMC environment.
Solution method: dsmcFoam+ implements an explicit time-stepping solver with stochastic molecular collisions appropriate for studying rarefied gas flow problems.
References: All appropriate methodological references are contained in the section entitled References.
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.
Present work investigates the performance of the Flamelet Generated Manifold combustion model in a marine-sized combustion chamber within the framework of RANS turbulence modeling using the software ...OpenFOAM. The dimensions involved, both in terms of nozzles (∼1 mm) and chamber diameter (500 mm), make a tabulated combustion model a convenient choice to keep the computational time low with reliable results. A validation of the mesh is shown, using liquid length and spray penetration of a single-nozzle injector configuration. Then the reacting cases are presented, both in single and multi-nozzle configuration. The results are promising and in good agreement with experiments, in terms of Ignition Delay Time (IDT), Lift-Off Length (LOL) and Ignition Location (IL). However, a shorter IDT is found in both configurations and mainly explained with the surrogate fuel used in simulation (n-Dodecane) being more reacting than the one used in experiments (Diesel). On the other hand, LOL shows good agreement, particularly in the multi-nozzle configuration. IL was available experimentally only for the single nozzle configuration, and the numerical value has shown spot-on results. Eventually, the effectiveness of the specific enthalpy as an additional control variable for the FGM manifold in capturing the cooling effect of the liquid spray injected is assessed. It is found that the larger the nozzle, and consequently the amount of liquid fuel injected, the larger the cooling on the surrounding gas is. Therefore, the introduction of multiple oxidizer temperature levels below the ambient initial temperature is strongly recommended in the tabulated chemistry method.
•RANS of marine-sized single- and multi-hole injectors.•FGM provides results in good agreement with experimental parameters.•Heat exchange without phase change is addressed.•Tabulated combustion requires enthalpy as control variable.
When a heat pipe is used as a cooling system for road vehicles, it is subject to acceleration which can adversely affect its thermal performance. In this study, we investigate the possibility of ...applying heat pipes for the cooling of power modules subject to time-varying power dissipation and time-dependent acceleration vectors whose projection along the heat pipe axis is up to 3g. The problem is tackled by modelling the heat pipe through a lumped parameter thermal network (LPTN). A numerical algorithm is used to solve the equations of LPTN representing the heat pipe. The code is then coupled with a 3D CFD solver (OpenFOAM) to perform a 1D/3D co-simulation and test the applicability of heat pipes as the cooling system in high-performance cars.
•Lumped Parameters Thermal Network to simulate heat pipes under acceleration;•1D/3D co-simulation with OpenFOAM to study power module temperature distribution;•Investigation, through an application, of the effect of accelerations on the thermal performance of heat pipes.
Data assimilation (DA) plays a crucial role in extracting valuable information from flow measurements in fluid dynamics problems. Often only time-averaged data is available, which poses challenges ...for DA in the context of unsteady flow problems. Recent works have shown promising results in optimizing Reynolds-averaged Navier–Stokes (RANS) simulations of stationary flows using sparse data through variational data assimilation, enabling the reconstruction of mean flow profiles.
In this study we perform three-dimensional variational data assimilation of sparse time-averaged data into an unsteady RANS (URANS) simulation by means of a stationary divergence-free forcing term in the URANS equations. Efficiency and speed of our method are enhanced by employing coarse URANS simulations and leveraging the stationary discrete adjoint method for the time-averaged URANS equations. The data assimilation codes were developed in-house using OpenFOAM for the URANS simulations as well as for the solution of the adjoint problem, and Python for the gradient-based optimization.
Our results demonstrate that data assimilation of sparse time-averaged velocity measurements not only enables accurate mean flow reconstruction, but also improves the flow dynamics, specifically the vortex shedding frequency. To validate the efficacy of our approach, we applied it to turbulent flows around cylinders of various shapes at Reynolds numbers ranging from 3000 to 22000. Our findings indicate that data points near the cylinder play a crucial role in improving the vortex shedding frequency, while additional data points further downstream are necessary to also reconstruct the time-averaged velocity field in the wake region.
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