Library OpenFOAM Research Articles

Heterogeneous Multi-Rate mass transfer models in OpenFOAM®

We implement the Multi-Rate Mass Transfer (MRMT) model for mobile–immobile transport in porous media (Haggerty and Gorelick, 1995; Municchi and Icardi, 2019 [1]) within the open-source finite volume library OpenFOAM® (Foundation, 2014). Unlike other codes available in the literature (Geiger et al., 2011 [2]; Silva et al., 2009), we propose an implementation that can be applied to complex three-dimensional geometries and highly heterogeneous fields, where the parameters of the MRMT can arbitrarily vary in space. Furthermore, being built over the widely diffused OpenFOAM® library, it can be easily extended and included in other models, and run in parallel. We briefly describe the structure of the multiContinuumModels library that includes the formulation of the MRMT based on the works of Haggerty and Gorelick (1995) and Municchi and Icardi (2020a). The implementation is verified against benchmark solutions and tested on two- and three-dimensional random permeability fields. The role of various physical and numerical parameters, including the transfer rates, the heterogeneities, and the number of terms in the MRMT expansions, is investigated. Finally, we illustrate the significant role played by heterogeneity in the mass transfer when permeability and porosity are represented using Gaussian random fields. Program summaryProgram Title: mrmtFoamCPC Library link to program files:https://dx.doi.org/10.17632/fkywm44j3y.1Developer’s repository link:https://github.com/multiform-UoN/mrmtFOAMLicensing provisions: GPL 3.0Programming language: C++Nature of problem: Large scale dynamics of heat and mass transfer in heterogeneous media where one mobile region coexists with multiple immobile regions.Solution method: The multi-rate mass transfer model is employed to described pre-asymptotic (i.e., non equilibrium ) transfer between regions. This method is implemented using the opensource finite volume library OpenFOAM®

Combined Two-phase Co-flow and Counter-flow in a Gas Channel/Porous Transport Layer Assembly

Polymer electrolyte fuel cells and electrolyzers are low temperature devices whereby both gases and liquids intermingle within the porous transport layers and open channels. The flow of the liquid and gas is of paramount importance to the functioning of the unit. This motion is poorly understood. Cell-level models typically employ volume-averaging techniques to describe the motion of the flowing reactants and products. Until recently, detailed analysis of the two-phase liquid gas mixture, employing front-tracking methods has proved too computationally prohibitive. Previous work [1,2] has considered the motion of liquid drops in gas channels, it being assumed the drops are formed at specific nucleation sites on the sides of the channels. The present work considers a detailed numerical analysis of combined liquid-gas co-flow in a gas channel with liquid-gas counter-flow in a porous transport layer (PTL). The geometry considered is a ‘T-shape’ with the porous transport layer in the form of a thin rectangular prism of dimensions 0.5×0.5×0.1 mm3 located at the base of the ‘T’, and the gas flowing across the top channel, as shown in Fig. 1. The PTL is reproduced by digital reconstruction of nano-computer tomography images of a Freudenberg H2315 PTL as a stereolithography file*, see Figure 2(a). From this, the domain is tessellated with an unstructured castellated, or octree, type mesh, Fig. 2(b). Liquid water is introduced at an electrode at the base of the PTL and gaseous oxygen is simultaneously removed by electrochemical reduction; the resulting liquid-gas counter-flow in the porous transport layer effects liquid droplets being entrained in co-flow in the gas channel and being convected downstream, thereafter.The equations of mass and momentum are solved by means of the open source software library OpenFOAM. A volume-of-fluid approach based on the multidimensional universal limiter for explicit solution was employed. At t = 0, the channel is presumed to be filled with gas, and the PTL partially saturated with liquid water. Gas is introduced at the inlet at a given velocity. Water is added and gas removed at the electrode (counter-flow), whereas both water and gas are removed at the outlet (co-flow). At the channel walls and on the PTL fibres, the static contact angle is fixed.Some results are shown in Fig. 3(a-d). It can be seen that the location and size of the drops shed varies somewhat in space and time, i.e., there is a stochastic component to the motion of the fluid, due to the spatial distribution of the fibres in the PTL, the transient shedding process, and the merging of liquid streams flowing into the gas channel. Nonetheless a definite periodicity is observed, with drops being injected into the channel at a fairly regular rate. Some relatively minor switching with time is observed within the PTL due to the random packing of fibres, but these transients are relatively quiescent. In addition to providing important new information about flow and pressure losses in electrochemical cells as a function of current density and stoichiometry, the present model may be also used to enumerate properties such as relative permeability which can subsequently be employed in cell-scale models.* The authors wish to thank Mr. Eugen Hoppe for constructing a stereolithography file of the porous material used in this study.[1] Andersson, M., Beale, S.B., Reimer, U., Lehnert, W., Stolten, D., Int. J. Hydrog. Energy, 2018, 43(5): 2961-2976.[2] Andersson, M., Mularczyk, A., Lamibrac, A., Beale, S.B., Eller, J., Lehnert, W., Büchi, F.N., J. Power Sources, 2018. 404: 159-171. Figure 1

A sharp-interface immersed boundary method for simulating high-speed compressible inviscid flows

This paper presents a robust sharp-interface immersed boundary method for simulating inviscid compressible flows over stationary and moving bodies. The flow field is governed by Euler equations, which are solved by using the open source library OpenFOAM. Discontinuities such as those introduced by shock waves are captured by using Kurganov and Tadmor divergence scheme. Wall-slip boundary conditions are enforced at the boundary of body through reconstructing flow variables at some ghost points. Their values are obtained indirectly by interpolating from their mirror points. A bilinear interpolation is employed to determine the variables at the mirror points from boundary conditions and flow conditions around the boundary. To validate the efficiency and accuracy of this method for simulation of high-speed inviscid compressible flows, four cases have been simulated as follows: supersonic flow over a 15 ° angle wedge, transonic flow past a stationary airfoil, a piston moving with supersonic velocity in a shock tube and a rigid circular cylinder lift-off from a flat surface triggered by a shock wave. Compared to the exact analytical solutions or the results in literature, good agreement can be achieved.

The ghost fluid method for OpenFOAM: A comparative study in marine context

The open source CFD library OpenFOAM is utilized to implement the ghost fluid method (GFM). The implemented solver GFMFoam is compared against the standard volume-of-fluid (VOF) solver interFoam in OpenFOAM. For both VOF solvers, the scalar transport equation is solved similarly but the discretization of the momentum and continuity equations differ between GFMFoam and interFoam. The two methods are compared in four test cases with mild surface deformation. First, the GFM implementation is validated. Second, the results on a 2 d interface shear layer highlight the importance of the viscous term treatment in the GFM. Third, the model scale Wiggley hull results indicate that the GFMFoam is more sensitive to the grid aspect ratio and resolution than interFoam but the viscous resistance is better predicted. Also, GFMFoam is shown to be less sensitive to numerical ventilation than interFoam. Fourth, the results from the Hamburg Test Case indicate a total resistance prediction within 1% when evaluated against reference data at model scale and 10% at full scale. Based on the steady state test cases of the present study, GFMFoam has moderate benefits over interFoam but it does not clearly outperform interFoam.

Effects of compressibility, three-dimensionality and air cavity on a free-falling wedge cylinder

The effects of fluid compressibility on the motions and hydrodynamic forces of a free-falling wedge are investigated using the Reynolds-Average Navier-Stokes (RANS) equations and volume of fluid (VOF) method which are implemented in the open-source library OpenFoam. The initial slamming, transition, collapse and post-closure stages during the water entry of the wedge with two Froude numbers are simulated using a dynamic mesh method. The interDyMFoam and compressibleInterDyMFoam solvers are applied in 2D and 3D water entry simulations considering multi-phase problems. The influences of the fluid compressibility and three-dimensionality on the acceleration, velocity, vertical motion and pressures on the entry body are studied. The peak values of pressures on the bottom and top surfaces of the wedge during slamming and air cavity closure stage, are analyzed together with the occurrence time of them.

Basic verification of a numerical framework applied to a morphology adaptive multifield two‐fluid model considering bubble motions

SummaryA morphology adaptive modeling framework is derived that is able to handle computationally efficiently dispersed as well as resolved interfacial structures coexisting in the computational domain with the same set of equations. The Eulerian multifield two‐fluid model is combined with the compact momentum interpolation method for multiple phases, which has been proposed in the literature as an extension to the Rhie‐Chow pressure‐velocity coupling. Additionally to the interfacial drag force, the virtual mass force is consistently accounted for in the model. Utilizing a specialized interfacial drag formulation, large interfacial structures can be described with the presented method in a volume‐of‐fluid‐like manner, additionally to the disperse description. The strong phase coupling due to the drag closure model in interfacial regions is resolved with a partial elimination algorithm, which is adapted to work in an approximate manner for more than two phases via a sum formulation. The presented model is implemented in the C++ library OpenFOAM and solver performance is compared with results obtained with the homogeneous model approach in two cases of a single rising gas bubble for two‐ and three‐dimensional space, respectively. Additionally, for both three‐dimensional cases, the results are compared with experimental data. Finally, the presented method's capability of representing dispersed and resolved interfacial structures at the same time is demonstrated with two test cases: a two‐dimensional gas bubble, rising in a liquid, which is laden with micro gas bubbles, and a two‐dimensional stagnant stratification of water and oil, sharing a large‐scale interface, which is penetrated by micro gas bubbles.

A computational fluid dynamics study by conjugate heat transfer in OpenFOAM: A liquid cooling concept for high power electronics

A conjugate heat transfer (CHT) study of a liquid cooling heat exchanger is carried out using the open source computational fluid dynamics (CFD) library OpenFOAM. The heat exchanger was 3D printed using aluminium and experimentally verified by temperature probing and thermal imaging. The functionality of the heat exchanger in cooling localized heat sources is demonstrated. Three different turbulence models were utilized including k-ω shear stress transport (SST) model, the standard k-ε model and large-eddy simulation (LES). The numerical results indicate that the k-ω SST and LES models produced similar results in terms of flow structures and temperature levels while the k-ε model deviated from the two other models. The scalability of the heat exchanger was numerically demonstrated by comparing the flow uniformity by varying the inlet Reynolds number between 4960 and 14880. The conclusions of the paper consists of the following main results. (1) The numerical results indicate that the flow uniformity in the channels is noted to be affected by the flow structures before and after the fin system. (2) The simulated hot-spot temperatures were noted to be relatively sensitive to the predicted flow laminarization inside the channels. (3) The heat exchanger was shown to be functional and to maintain cool surface temperatures in the simulations and the experiments. Additionally, the used CHT solver in OpenFOAM is tested and verified in different ways.

CFD modeling of the [formula omitted] capture by range hood in a full-scale kitchen

Air quality criteria in residential houses are increasing continuously. Multiple studies tend to use commercial CFD software in order to predict and optimize the flow conditions in range hoods. Most of them modeled the range hood without considering the rotating fan. In the present work, a new open-source solver was developed using the OpenFoam libraries. It is based on a buoyancy Boussinesq solver and a turbulent passive scalar transport equation accounting for the heated CO2 extraction by the rotating fan, fully modeled using the Multiple reference frame (MRF) approach. The new solver is carefully validated against experimental results for three benchmark cases: a CO2 plume, a differential heated cavity and the performance curve of a rotating fan. The model has been confidently used to model the CO2 extraction in a realistic residential kitchen considering one to four burners on. An improvement of 30% in the capture efficiency is reached by increasing the extraction flowrate of the fan from 100 to 300 cfm. An extraction efficiency of 100% is observed for flowrates above 330 cfm.

Numerical simulation of crust freezing in processed meat: A fully coupled solid–fluid approach

We present a numerical model for the simulation of continuous impingement freezing of processed food products. This model is capable of fully describing the fluid dynamics of the non-isothermal flow field, including turbulence with conjugate heat transfer (CHT). The motion of the solid region is captured by advecting the solid rathe than employing a moving mesh algorithm, resulting in a model that is more computationally efficient. This methodology is implemented as a numerical solver using the well-known open-source library OpenFOAM. Our results confirm that the proposed model can provide detailed insight on the freezing process at a minimum computational cost.

New boundary conditions for simulating the filling stage of the injection molding process

PurposeThe purpose of this paper is to develop new boundary conditions for simulating the injection molding process of polymer melts.Design/methodology/approachThe boundary conditions are derived and implemented to simulate real-life air vents (used to allow the air escape from the mold). The simulations are performed in the computational library OpenFOAM® by considering two different fluid models, namely, Newtonian and generalized Newtonian (Bird–Carreau model).FindingsA detailed study on the accuracy of the solver interFoam for simulating the filling stage is presented, by considering simple geometries and adaptive mesh refinement. The verified code is then used to study the three-dimensional filling of a more complex geometry.Originality/valueThe results obtained showed that the numerical method is stable and allows one to model the filling process, simulating the real injection molding process.

Macroscopic models for filtration and heterogeneous reactions in porous media

Derivation of macroscopic models for advection-diffusion processes in the presence of dominant heterogeneous (e.g., surface) reactions using homogenisation theory or volume averaging is often deemed unfeasible (Valdés-Parada et al., 2011; Battiato and Tartakovsky, 2011a) due to the strong coupling between scales that characterise such systems. In this work, we show how the upscaling can be carried out by applying and extending the methods presented in Allaire and Raphael (2007), Mauri (1991). The approach relies on the decomposition of the microscale concentration into a reactive component, given by the eigenfunction of the advection-diffusion operator, the associated eigenvalue which represents the macroscopic effective reaction rate, and a non-reactive component. The latter can be then upscaled with a two-scale asymptotic expansion and the final macroscopic equation is obtained for the leading order. The same method can also be used to overcome another classical assumption, namely of non solenoidal velocity fields, such as the case of deposition of charged colloidal particles driven by electrostatic potential forces. The whole upscaling procedure, which consists in solving three cell problems, is implemented for arbitrarily complex two- and three-dimensional periodic structures using the open-source finite volume library OpenFOAM®. We provide details on the implementation and test the methodology for two-dimensional periodic arrays of spheres, and we compare the results against fully resolved numerical simulations, demonstrating the accuracy and generality of the upscaling approach. The effective velocity, dispersion and reaction coefficients are obtained for a wide range of Péclet and surface Damköhler numbers, and for Coulomb-like forces to the grains. Noticeably, all the effective transport parameters are significantly different from the non-reactive (conserved scalar) case, as the heterogeneity introduced by the reaction strongly affects the micro-scale profiles.

Numerical Study of a Novel Concept for Manufacturing Savonius Turbines with Twisted Blades

This work presents a numerical study of the aerodynamic performance and the resulting flow field of two novel Savonius wind turbines with twisted blades. The novelty relies on the blade manufacturing process which is characterized by a ‘twisted cut’ through the central axis of a hollow cylinder (tube), followed by a partial twisted cut in the range of 90°. This approach does not require any expensive fabrication process such as blade molding and/or 3D prints, and, therefore, it can potentially mitigate the production costs. The main goal is to investigate the operational parameters and the overall performance of the presented devices, which are currently being operated in atmospheric conditions. For this purpose, three-dimensional simulations have been performed using the open-source CFD library OpenFOAM in order to solve the governing equations and for characterizing the main phenomena involved in the flow pattern. The Reynolds-averaged Navier–Stokes (RANS) approach together with the k − ω SST model were employed to reproduce the flow turbulence effects. This model is validated using wind tunnel measurements of the power ( C P ) and torque ( C M ) coefficients from a straight blade Savonius turbine. Unsteady simulations of the two turbine prototypes were investigated at different tip speed ratio TSR ( λ ) by varying the rotational speed of the rotor while keeping constant the free stream (rated) velocity V ∞ . The results were compared against the Savonius turbine employed for validating the model. Aerodynamic loads and general wake structure were studied at the optimal operational conditions as well. For the same turbine configurations, the new blade geometry improved the performance by 20–25% (at its optimal TSR), compared to the conventional straight blade Savonius rotor, as well as the reducing torque fluctuation.

Geometrical influence of the source/drains configuration on the flow interactions in a sandbox model: A three-dimensional OpenFOAM simulation

This paper explores the interaction of different flow paths in a porous medium by observing the effect of having more than one drain in a simple model domain with a single source. The work is based on three-dimensional numerical simulations of the flow of injected water in a sandbox domain with porous volume completely filled by water and oil. The calculation uses the OpenFOAM library to solve Darcy’s equations for the dynamics of a two-phase flow: water as the wetting, oil as the nonwetting fluid. We observe the interactions of flows in different paths under changes of number of drains and their relative positions.

The OFFBEAT multi-dimensional fuel behavior solver

The OpenFOAM Fuel BEhavior Analysis Tool, or OFFBEAT, is a multi-dimensional fuel performance code under collaborative development at the Laboratory for Reactor Physics and Systems Behaviour (LRS) of the EPFL and at the PSI. The code can be used both for studying complex 2D or 3D local effects and for more traditional 1.5D base irradiation analyses. OFFBEAT is based on the open-source C++ library OpenFOAM®, thus the governing equations are discretized with modern finite volume techniques using unstructured meshes, and the solver is fully parallelized via geometrical domain decomposition. This paper presents the numerical framework, governing equations and solution strategy behind OFFBEAT and it gives a brief overview of the material properties and behavioral models already implemented. Finally, a set of experimental rods is chosen to provide the first validation results for the thermal behavior of low burnup axisymmetric rods, by comparing the fuel centerline temperatures with experimental data.

Three-dimensional simulations of liquid waves in isothermal vertical churn flow with OpenFOAM

Periodic liquid waves of large amplitude are one of characteristic phenomena observed in the churn flow regime of gas–liquid flow in vertical conduits, where the liquid flowing on the wall is entrained upwards by the gas flow in the core. The present work investigates the frequency of these large liquid waves. Three-dimensional simulations of isothermal churn flow of air and water in 19 and 32 mm vertical pipes were performed using the interFoam solver from the OpenFOAM library. Turbulent features in the flow are modelled using the unsteady Reynolds Averaged Navier–Stokes approach with the k–ω SST (shear stress transport) model. Interface sharpening with bounded compression was used to preserve the sharpness of gas–liquid interface by compensating the diffusive fluxes of the numerical scheme. A sensitivity study on the global amount of interface compression was performed for two flow cases taken from the literature. Mesh sensitivity study was performed using four meshes, ranging from a coarse mesh with several hundred thousand cells, to a fine mesh with several million computational cells. Results for the calculated wave frequency and wave maximum amplitude agree with measured values reported in the literature.

Flow and Scour Analysis Around Monopole of Fixed Offshore Platform Using Method that Couples Computational Fluid Dynamics and Discrete Element Method

When an offshore foundation is exposed to waves and currents, local scour could develop around a pile and even lead to structural failure. Therefore, understanding and predicting the scour due to sediment transport around foundations are important in the engineering design. In this study, the flow and scour around a monopole foundation exposed to a current were investigated using a method that coupled the computational fluid dynamics (CFD) and discrete element method (DEM). The open source computation fluid dynamics library OpenFOAM and a sediment transport library were coupled in the OpenFOAM platform. The incipient motion of the particle was validated. The flow fields and sediment transport around the monopole were simulated. The scour depth development was simulated and compared with existing experimental data. For the upstream scour hole, the equilibrium scour depth could be reproduced qualitatively, and it was underestimated by about 23%.

A computational framework with an adaptive mesh refinement technique for concentrated suspension flows

A computational framework (solver) is developed for incompressible isothermal concentrated non-colloidal suspension flows of rigid particles. The number of particles can be of the order of millions. The developed solver, named “SuspensionFoam” can predict the phenomenon of shear-induced migration in complex geometries in a continuum mechanics modeling approach. It employs the C++ object-oriented OpenFOAM library features including adaptive mesh refinement (AMR), dynamic mesh rotation in both 2D and 3D, adaptive time steps, multi-CPU parallel-run over MPI (and open MPI) and run-time selection of different liquid and particles properties (i.e. diameter, maximum packing). Three different numerical examples have been conducted by simulating isodense suspension flow in a vertical Couette cell, non-isodense resuspension and mixing of particles in a horizontal Couette cell, and isodense suspension flow in a conduit. The present AMR technique is found to reduce the computational process considerably, with a good accuracy. Numerical results are presented and discussed, with comparisons to experimental data.

Numerical Study of an Isothermal Slush Flow for Aerospace Propulsion Applications

Abstract Slushes are two-phase solid-liquid single-species cryogenic fluids that exhibit an increased density and a greater heat capacity with respect to the corresponding normal boiling point liquids. These promising features are of large interest for applications that exploit slush as a thermal fluid, like super magnets refrigeration, cryogenic cooling of bio-materials or air conditioning, and for aerospace systems that use slush fluids as fuel or oxidizer. Several programs in the frame of the research on Slush Hydrogen (SLH2) as a new-generation fuel for aerospace propulsion have been started in the past. This work was carried out in the framework of a VKI research activity promoted by the Predict ESA Technology Research Programme, to investigate experimentally and numerically the behavior of slush flows in a representative upper stage feeding line. In this paper, we present a simulation based on a granular two-fluid model on an isothermal solid liquid mixture (slurry) and a Nitrogen slush (SLN2) fluid flowing in a horizontal pipe. A finite-volumes discretization using the software library OpenFOAM was benchmarked against experimental and numerical literature data, to assess the accuracy of the code in predicting pressure drops along the pipe axis and solid particle distribution across the pipe diameter. Moreover, the effects of concentration and inlet velocity are investigated. We show that the numerical model fairly reproduces the literature data in terms of important aspects as the solid volume fraction distribution and the pressure drops, especially for high flow rates.

An open-source density-based solver for two-phase [formula omitted] compressible flows: Verification and validation

A density-based solver based on the OpenFoam library coupled with a tabulated equation of state is developed. The Navier–Stokes characteristic boundary condition is considered to guarantee the accuracy and stability of the simulation. Firstly, two validation test cases are considered to illustrate the solver capability. Then, the flows in two converging-diverging nozzles are simulated under supercritical and subcritical conditions. A good agreement in terms of pressure distribution is obtained for all nozzles. The bulk viscosity and turbulence effects are then carefully assessed. The bulk viscosity does not affect significantly the predictions of the new solver, whereas it is of prime importance to well model the thermal and flow fields up to the wall. Finally, it is recommended to use an unsteady density-based solver for CO2 flows in converging-diverging nozzles associated with a Homogeneous Equilibrium Model and the k-ω SST closure to get the best overall predictions.

Numerical Investigation of Different Dynamic Contact Angle Models for a Droplet Impacting a Surface in OpenFOAM

Computational Fluid Dynamics (CFD) is used to study the spreading process of a water droplet with a radius of 0.00275mm impacting a wax surface at a velocity of 1.18ms−1 . This type of flow is considered to be Multiphase, incompressible, laminar, surface tension dominated and is governed by the Navier stokes and continuity equations. To accurately model the spreading process 3 different contact angle models are investigated, two of which take into account the moving contact line. The governing equations are solved using the open source C++ library OpenFOAM, which uses a Finite Volume Method (FVM) of discretization and a Volume Of Fluid (VOF) interface capturing method. The VOF method is known to produce unphysical velocities when high pressure gradients exist between the two phases, thus a numerical improvement is implemented to reduce the magnitudes of the unphysical velocities. The improvement reduces the magnitudes of the unphysical velocities and as shown in literature their magnitudes increase with an increase in surface tension dominance. The improvement is implemented together with different contact angle models and results obtained show that contact angle models that take into account the moving contact line gives a good correlation of the spreading diameter obtained numerically with the one obtained experimentally.