OpenFOAM Simulations Research Articles

Analysis of energy occupying ratio of Coulomb explosion and thermal effect in picosecond pulse laser processing

Molten material recasting may occur in ten picosecond laser processing although ultrashort-pulse processing is a kind of cold working method. It is also proved that experimental results do not fit expected processing results well in ten picosecond laser processing. What is more, some cracks on the surface of workpiece processed in ten picosecond laser can be observed. Aimed at above-mentioned facts processing in ten picosecond laser, a new hybrid model is raised. In this model, not only Coulomb explosion which is known to us but also thermal effect occurs in ten picosecond laser processing. Experiment method is used for analyzing the energy ratio of the two parts (Coulomb explosion and thermal effect). With OPENFOAM simulation software, the radius, topography and crack location of slots processed in different energy density are simulated. Finally, a comparison between simulation result and experimental result proves that this hybrid model is high degree of applicability and accuracy.

Predicting Lean Blowout and Emissions of Aircraft Engine Combustion Chamber Based on CRN

Abstract To predict the pollutant emissions and lean blowout, chemical reactor network (CRN) model is applied to the modern aircraft engine combustion chamber. In this study, the CRN which represent the major features of aerodynamics and combustion in the combustion chamber is set up based on the OpenFOAM simulation results. The boundary and the initial conditions used for the CRN derive from the operating modes of typical aircraft engine cycle. A 21 species 30 steps chemical mechanism of kerosene is employed in the CRN method. The levels of pollutant emissions are obtained under four ICAO engine power settings of idle, approach climb and take off. The lean blowout equivalent ratio is evaluated at the idle power setting. The results will be helpful to predict the aircraft engine exhaust emissions and lean blowout (LBO).

New inflow boundary conditions for modeling twisted wind profiles in CFD simulation for evaluating the pedestrian-level wind field near an isolated building

The hilly topography of Hong Kong influences oncoming winds and gradually changes their wind directions along the profiles' height. The vertical variation in wind directions, or the twist effect, significantly influences the Pedestrian Level Wind (PLW) field in urban areas of Hong Kong, thus it is a topic demanding systematic investigations. In this study, a new set of inflow boundary conditions are proposed to model twisted wind flows in Computational Fluid Dynamic (CFD) simulations. The new inflow boundary condition derived based on the horizontal homogeneous assumption, specifies a vertical profile of lateral wind speeds at the inlet boundary to sustain the twist effect in the empty computational domain. The proposed boundary conditions are used to simulate the PLW fields near three isolated buildings with different Height-to-Width ratio using two CFD codes; OpenFOAM, and FLUENT. The results reveal that OpenFOAM is more reliable in simulating PLW fields in twisted wind flows using the new set of boundary conditions. The three-dimensional flow field provided by the OpenFOAM simulation shows sparse streamlines downstream the buildings, indicating lack of organized eddies in the building far wake, which negatively affects the dispersion of air pollutants in twisted winds.

Comparison of different approaches tracking a wing-tip vortex

This paper compares the performance of different grid based and grid free modelling approaches to predict the tip vortex evolution in both near and far wing wake fields. The grid based methods cover different turbulence modelling approaches, adaptive mesh refinement and the adaptive vorticity confinement (VC) method using the OpenFOAM code. Computational vortex method (CVM) coupled with the OpenFOAM simulation of the near field is utilised to properly predict the tip vortex behaviour in the far field. All simulation results are compared to results of the wind tunnel experiments conducted by Devenport et al. (1996). The comparison is based on the analysis of the vortex core parameters: the core size, the peak tangential velocity and the axial velocity deficit. Additionally, the results are compared with another numerical study by Wells (2009, 2010). It turns out that turbulence modelling plays an important role since simple one and two-equation models overpredict the turbulence intensity in the vortex core resulting in its fast decay. The potential of the adaptive VC method depends on the underlying turbulence model. Grid free vortex method shows a good potential to improve the simulation accuracy.

NUMERICAL ANALYSES OF OPENFOAM'S OVERTOPPING DEVICE SOLUTION

Studies related to ocean energy are getting more important lately, once world claims for renewable energy usage. The Overtopping Device is a kind of Ocean Waves Energy Converter (OWEC), which main concept is storing water provided by incident waves above sea level to feed a set of low head turbines. In order to obtain the desired effect, this device contains a ramp which elevates the incident waves toward the reservoir. Present study aims to perform a numerical model of a 2D Overtopping Device by means of OpenFOAM simulations. OpenFOAM is a free open source code which has shown applicability in many areas of engineering. The adopted solver (InterFOAM) is Volume of Fluid based (VOF) according to Finite Volume Method (FVM), these methodologies has been largely used among researchers in propagating waves field. FLUENT (commercial code) is used to verify OpenFOAM's results. Once, the main point of this paper is to present OpenFOAM as a considerable tool for propagating waves studies, it firstly presents a numerical wave verification with analytical solutions (second order Stokes theory). The second section of results presents overtopping time series peaks in 100 s of simulation. Also, by mass flow rate integration, it presents total mas of water climbed to the reservoir. The integration of mass flow rate takes 94 s of simulation (not 100 s) because it is noticeable a pause between two peaks of overtopping at that time. Results show agreement between wave elevation and wave velocity profiles with straight convergence of periods between analytical and numerical waves. Most important differences are found near air/water interface, owed to faster air flow at that region. Generally OpenFOAM and FLUENT results are similar, with converged overtopping time series peaks and their magnitudes too. Similarly, the amount of water marked by both software are close with very similar trend lines.

Benchmarking computational fluid dynamics models of lava flow simulation for hazard assessment, forecasting, and risk management

Numerical simulations of lava flow emplacement are valuable for assessing lava flow hazards, forecasting active flows, designing flow mitigation measures, interpreting past eruptions, and understanding the controls on lava flow behavior. Existing lava flow models vary in simplifying assumptions, physics, dimensionality, and the degree to which they have been validated against analytical solutions, experiments, and natural observations. In order to assess existing models and guide the development of new codes, we conduct a benchmarking study of computational fluid dynamics (CFD) models for lava flow emplacement, including VolcFlow, OpenFOAM, FLOW-3D, COMSOL, and MOLASSES. We model viscous, cooling, and solidifying flows over horizontal planes, sloping surfaces, and into topographic obstacles. We compare model results to physical observations made during well-controlled analogue and molten basalt experiments, and to analytical theory when available. Overall, the models accurately simulate viscous flow with some variability in flow thickness where flows intersect obstacles. OpenFOAM, COMSOL, and FLOW-3D can each reproduce experimental measurements of cooling viscous flows, and OpenFOAM and FLOW-3D simulations with temperature-dependent rheology match results from molten basalt experiments. We assess the goodness-of-fit of the simulation results and the computational cost. Our results guide the selection of numerical simulation codes for different applications, including inferring emplacement conditions of past lava flows, modeling the temporal evolution of ongoing flows during eruption, and probabilistic assessment of lava flow hazard prior to eruption. Finally, we outline potential experiments and desired key observational data from future flows that would extend existing benchmarking data sets.

Euler–euler anisotropic gaussian mesoscale simulation of homogeneous cluster‐induced gas–particle turbulence

An Euler–Euler anisotropic Gaussian approach (EE‐AG) for simulating gas–particle flows, in which particle velocities are assumed to follow a multivariate anisotropic Gaussian distribution, is used to perform mesoscale simulations of homogeneous cluster‐induced turbulence (CIT). A three‐dimensional Gauss–Hermite quadrature formulation is used to calculate the kinetic flux for 10 velocity moments in a finite‐volume framework. The particle‐phase volume‐fraction and momentum equations are coupled with the Eulerian solver for the gas phase. This approach is implemented in an open‐source CFD package, OpenFOAM, and detailed simulation results are compared with previous Euler–Lagrange simulations in a domain size study of CIT. The results demonstrate that the proposed EE‐AG methodology is able to produce comparable results to EL simulations, and this moment‐based methodology can be used to perform accurate mesoscale simulations of dilute gas–particle flows. © 2017 American Institute of Chemical Engineers AIChE J, 63: 2630–2643, 2017

CFD simulations of a bubble column with and without internals by using OpenFOAM

Bubble column reactors are widely employed in various applications. Nowadays computational fluid dynamics (CFD) provides the state-of-the-art capabilities of simulating the hydrodynamics in these reactors. In the present work, bubble column is numerically simulated by using open source CFD tool, OpenFOAM 2.3.1. Euler-Euler two-fluid model is used for the simulations. In the first part, OpenFOAM simulations are validated with experimental data from the literature over a column diameter range of 138–600mm and the superficial gas velocity in the range of 19–169mm/s. The velocity and holdup patterns as well as circulation patterns in the bubble column are compared. In addition, Fluent® simulations are performed for the same conditions in order to compare the accuracy of OpenFOAM solvers. In the second part of the work, the validated OpenFOAM solver is applied to simulate the flow field in the 120mm ID bubble column with and without internals. The internals consisted of (a) one vertical central rod of 36mm diameter, (b) one central rod of (a) and four vertical additional rods of 12mm diameter, (c) one central rod of (a) and fourteen vertical additional rods of 12mm diameter. The OpenFOAM simulations are found to be in good agreement with the experimental data for both bubble columns with and without internals. As regards to experiments, radial profiles of gas hold-up and the liquid velocity were measured by using the radioactive particle technique (RPT). Such measurements were made at four axial locations.

Influence of blockage effect on measurement by vane anemometers

The article deals with influence of blockage effect caused by vane anemometer in the wind tunnel by measurement via this anemometer. The influences will be represented by correction coefficient. The first part of this article is focused on the design of the impeller of vane anemometers. The impellers are printed on 3D printer with variable parameters. The anemometer is fixed in an open section of the wind tunnel with closed loop and the velocity profile is measured by Laser Doppler velocimetry (LDV) in front and behind it for all impellers. The experimental data are compared with the numerical simulation in OpenFOAM. The results are correction coefficients.

Large-Eddy Simulation of a Reacting Jet in Cross Flow With NOx Prediction

The reduction of full and part load emissions and the increase of the turndown ratio are important goals for gas turbine combustor development. Combustion techniques, which generate lower NOx emissions than unstaged premixed combustion in the full load range, and which have the potential of reducing minimum load while complying with emission legislation, are of high technical interest. Therefore, axial-staged combustion systems have been designed, either with or without expansion in a turbine stage between both stages. In its simpler form without intermediate expansion stage, a flow of hot combustion products is generated in the first stage of the premixed combustor, which interacts with the jets of premixed gas injected into the second stage. The level of NOx formation during combustion of the premixed jets in the hot cross flow determines the advantage of axially staged combustion regarding full load NOx emission reduction. Employing large-eddy simulation in openfoam, a tool has been developed, which allows to investigate staged combustion systems including not only temperature distribution but also NOx emissions under engine conditions. To be able to compute NOx formation correctly, the combustion process has to be captured with sufficient level of accuracy. This is achieved by the partially stirred reactor model. It is combined with a newly developed NOx model, which is a combination of a tabulation technique for the NOx source term based on mixture fraction and progress variable and a partial equilibrium approach. The NOx model is successfully validated with generic burner stabilized flame data and with measurements from a large-scale reacting jet in cross flow experiment. The new NOx model is finally used to compute a reacting jet in cross flow under engine conditions to investigate the NOx formation of staged combustion in detail. The comparison between the atmospheric and the pressurized configuration gives valuable insight in the NOx formation process. It can be shown that the NOx formation within a reacting jet in cross flow configuration is reduced and not only diluted.

Comparison of two LES codes for wind turbine wake studies

For the third time a blind test comparison in Norway 2013, was conducted comparing numerical simulations for the rotor Cp and Ct and wake profiles with the experimental results. As the only large eddy simulation study among participants, results of the Technical University of Denmark (DTU) using their in-house CFD solver, EllipSys3D, proved to be more reliable among the other models for capturing the wake profiles and the turbulence intensities downstream the turbine. It was therefore remarked in the workshop to investigate other LES codes to compare their performance with EllipSys3D. The aim of this paper is to investigate on two CFD solvers, the DTU's in-house code, EllipSys3D and the open-sourse toolbox, OpenFoam, for a set of actuator line based LES computations. Two types of simulations are performed: the wake behind a signle rotor and the wake behind a cluster of three inline rotors. Results are compared in terms of velocity deficit, turbulence kinetic energy and eddy viscosity. It is seen that both codes predict similar near-wake flow structures with the exception of OpenFoam's simulations without the subgrid-scale model. The differences begin to increase with increasing the distance from the upstream rotor. From the single rotor simulations, EllipSys3D is found to predict a slower wake recovery in the case of uniform laminar flow. From the 3-rotor computations, it is seen that the difference between the codes is smaller as the disturbance created by the downstream rotors causes break down of the wake structures and more homogenuous flow structures. It is finally observed that OpenFoam computations are more sensitive to the SGS models.

Prediction of pressure drop and heat transfer coefficient in helically grooved heat exchanger tubes using large eddy simulation

Geometry of internally grooved tubes plays a significant role in the performance of heat exchangers. Although there are extensive databases of measurement data for some grooved tubes, it is generally challenging to predict the performance of nonexisting groove shapes. A computational fluid dynamics model based on wall-resolved large eddy simulation of turbulent pipe flow with heat transfer is proposed by using OpenFOAM simulation environment. Fully developed turbulence was simulated by solving the 3D unsteady Navier–Stokes equation in streamwise periodic variables. Simulations for a smooth pipe and a helically grooved tube were carried out at Re = 10,000 to 20,000. Mesh dependency study was performed. Simulation methodology was validated by collating simulated results with literature data and own measurements. The proposed model proved to be accurately predictive: 3.2% to 4.2% difference was found between simulations and measurements. The major novelties of this paper are the introduction of large eddy simulation technique in a new application area, validation for single-phase flow in the given Reynolds number regime, and guidelines for future modellers. This methodology can be used for optimizing parameters of future heat exchanger systems leading to more compact size and better performance.

Numerical Studies of Viscoelastic Flow Using the Software OpenFOAM

AbstractViscoelastic fluids are a special class of non‐Newtonian fluids. There are several types of viscoelastic fluid models, and all of them have a complex rheological response in comparison to Newtonian fluids. This response can be viewed as a combination of viscous and elastic effects and non‐linear phenomena. This complex physics makes a numerical simulation a rather challenging task, even in simple test‐cases. Studies presented in this paper are numerical studies of the viscoelastic fluid flow in several test cases. These studies have been done in OpenFOAM, an open‐source CFD package. Implementation of viscoelastic models and a solver is only available in a community driven version of software (OpenFOAM‐ext). One of the goals of research in this paper was to test the solver and models on some simple test cases. We considered start‐up and pulsating flows of viscoelastic fluid in a channel and a circular pipe. The important thing is that an analytical solution can be found in these cases, making in possible to test all aspects of numerical simulation in OpenFOAM. Obtained results showed an excellent agreement with the analytical solution for both velocity and stress components. These results encouraged authors' motivation and a choice to use OpenFOAM for simulation of viscoelastic flows. We hope that our research will make a contribution to the OpenFOAM community. Our plan for the further research is a simulation of blood flow in arteries with the viscoelastic solver. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Numerical Simulation of Drilling with Pulsed Beams

Electron beam drilling is an efficient method for microperforation. The technique using an electron beam for melting up and blowing out the material works in vacuum. Ablation is mainly based on the expulsion of the molten material by two competing mechanisms: evaporation of the workpiece as well as of the backing material. In this contribution a numerical finite volume OpenFOAM simulation model for beam-matter interaction in electron beam drilling is presented showing the transient dynamics of the process as well as the influence of various processing parameters.

High-vacuum thermionic converter

EOF-Library is a software that couples Elmer and OpenFOAM simulation packages. It enables efficient internal field interpolation and communication between the finite element and the finite volume frameworks. The coupling of the two packages is based on the Message Passing Interface, which results in low latency, high data bandwidth and parallel scalability. Potential applications are magnetohydrodynamics, convective cooling of electrical devices, industrial plasma physics and microwave heating. In this work we introduce the software and perform interpolation accuracy and parallel scaling tests by sending a known scalar distribution between the two codes.

Device measures transistor switching time

EOF-Library is a software that couples Elmer and OpenFOAM simulation packages. It enables efficient internal field interpolation and communication between the finite element and the finite volume frameworks. The coupling of the two packages is based on the Message Passing Interface, which results in low latency, high data bandwidth and parallel scalability. Potential applications are magnetohydrodynamics, convective cooling of electrical devices, industrial plasma physics and microwave heating. In this work we introduce the software and perform interpolation accuracy and parallel scaling tests by sending a known scalar distribution between the two codes.