In this paper, the effects of interpolation methodology on the accuracy of computed solutions are discussed in the context of unstructured overset grids. An in-house implementation of the overset ...method for OpenFOAM, OPERA (Chandar, 2015; Chandar et al., 2015) has been used. Several verification and validation studies reported previously used a simple interpolation technique such as inverse distance weighting and this was found to be adequate for prediction of forces. For closed problems however, the force history is plagued with unphysical oscillations. Also, a quantitative assessment of interpolation errors is lacking. The current work aims to understand the effects of interpolation error on conservation and how this error can be minimized by enforcing flux correction and/or better interpolation techniques. Apart from enforcing conservation, the pressure equation needs to be adjusted as well in an implicit manner to guarantee the transfer of fluxes correctly between overlapping regions. Importance of conservation and higher order interpolation are also discussed in the context of multiphase flows.
The porous media theory is extensively used to simulate the porous structures due to the complexity of the shape and grain configuration. In this study, The open-source code OpenFOAM was firstly ...extended to solve the interaction between the sloshing flow and the random porous structure, and the accuracy of the extension was validated by comparing the numerical results with experimental data. In addition, the effect of porosity, average diameter of the porous structure was analyzed, and then the anti-sloshing performance of rectangular tank for different excitation frequencies and distances between the random porous structure and the nodal line of eigenmode (m = 1) was also discussed. After that, a comparison of the wave-damping performance between the random porous layer and the traditional perforated baffle was conducted. Results indicated that the random porous structure with porosity (n) of 0.2 and average diameter (d50/b) of 0.85 has the best anti-sloshing performance, and the anti-sloshing performance of random porous layer is generally decreased when the excitation frequency moves close to the first-order natural frequency, and it is decreased with the increasing distance. A better wave-damping performance of the present random porous structure can be observed when compared with traditional perforated baffle.
•The anti-sloshing performance of the random porous layer in the water tank is numerically analyzed.•Porous media theory is adopted to simulate the random porous layer in the water tank.•The parameters of the porosity (n) and averaged diameter (d50) are optimized, and the effects of excitation frequencies and distances between the random porous layer and nodal line of eigenmode m = 1 are analyzed.•A comparison of the wave-damping performance between the present porous layer and the traditional porous baffle is conducted.•The water surface elevation, flow field, pressure on bulkhead and global average velocity in the water tank are investigated.
•A user-defined solver for biomass steam gasification in fluidized bed is built.•The solver is tested against experimental data in literature and works well.•Biomass steam gasification in the DFB at ...UBC is preliminary predicted.•Flue gas and syngas can be well separated by the U-bend and cyclone.•Dry N2-free syngas is composed of 55% H2, 20% CO, 20% CO2 and 5% CH4.
A user-defined solver integrating the solid-gas surface reactions and the multi-phase particle-in-cell (MP-PIC) approach is built based on the OpenFOAM software. The solver is tested against experiments. Then, biomass-steam gasification in a dual fluidized bed (DFB) gasifier is preliminarily predicted. It is found that the predictions agree well with the experimental results. The bed material circulation loop in the DFB can form automatically and the bed height is about 1m. The voidage gradually increases along the height of the bed zone in the bubbling fluidized bed (BFB) of the DFB. The U-bend and cyclone can separate the syngas in the BFB and the flue gas in the circulating fluidized bed. The concentration of the gasification products is relatively higher in the conical transition section, and the dry and nitrogen-free syngas at the BFB outlet is predicted to be composed of 55% H2, 20% CO, 20% CO2 and 5% CH4.
Combustion of hydrogen can take place in different modes such as laminar flames, slow and fast deflagrations and detonations. As these modes have widely varying propagation mechanisms, modeling the ...transition from one to the other presents a challenging task. This involves implementation of different sub-models and methods for turbulence-chemistry interaction, flame acceleration and shock propagation. In the present work, a unified numerical framework based on OpenFOAM has been evolved to simulate such phenomena with a specific emphasis on the Deflagration to Detonation Transition (DDT) in hydrogen-air mixtures. The approach is primarily based on the transport equation for the reaction progress variable. Different sub-models have been implemented to capture turbulence chemistry interaction and heat release due to autoignition. The choice of sub-models has been decided based on its applicability to lean hydrogen mixtures at high pressures and is relevant in the context of the present study. Simulations have been carried out in a two dimensional rectangular channel based on the GraVent experimental facility. Numerical results obtained from the simulations have been validated with the experimental data. Specific focus has been placed on identifying the flame propagation mechanisms in smooth and obstructed channels with stratified initial distribution. In a smooth channel with stratified distribution, it is observed that the flame surface area increases along the propagation direction, thereby enhancing the energy release rate and is identified to be the key parameter leading to strong flame acceleration. When obstacles are introduced, the increase in burning rate due to turbulence induced by the obstacles is partly negated by the hindrance to the unburned gases feeding the flame. The net effect of these competing factors leads to higher flame acceleration and propagation mechanism is identified to be in the fast deflagration regime. Further analysis shows that several pressure pulses and shock complexes are formed in the obstacle section. The ensuing decoupled shock-flame interaction augments the flame speed until the flame coalesces with a strong shock ahead of it and propagates as a single unit. At this point, a sharp increase in propagation speed is observed thus completing the DDT process. Subsequent propagation takes place at a uniform speed into the unburned mixture.
•Numerical modeling of deflagration to detonation transition using OpenFOAM.•Validation of turbulent flame closure models for lean mixtures at high pressure.•Effect of obstacles and stratified distribution on flame acceleration.•Mechanism of deflagration to detonation transition through shock-flame interaction.
In this article, using the direct simulation Monte Carlo (DSMC) method, the gas flow inside the gas centrifuge was modeled simultaneously in the Knudsen and hydrodynamic zones. So that the ...three-dimensional (3D) simulation of gas centrifuge in the presence of all drivers inside the rotor, including feed, scoop, baffle, etc. was done. The results showed that, the feed is an important factor in creating and intensifying the axial flow formed in the rotor axis, and choke phenomenon occurs at the point of its entry into the rotor. It was further revealed that the amount of separation power obtained from the simulation (using the DSMC method) and the experimental has a difference of 4.3%, showing the agreement of the 3D simulations with reality.
•Scoop is responsible for extracting flow and driving axial flow.•Pressure, temperature and molecules collision velocity with scoop inlet affect the drag force in this area.•Due to high rotor wall velocity, supersonic flow hits the scoop, and shock phenomenon occurs.•Feed is an important factor in creation and intensification of axial flow.•The difference in separation power obtained from simulation and experimental is acceptable (4.3%).
Coastal desalination plants have increased in number and size over the past decades due to the water crisis in the world. During the process of desalination, in addition to fresh water, brine with ...higher salinity than seawater is also produced that is commonly discharged back into the sea through the marine outfalls. This study aimed to numerically investigate the mixing and geometrical characteristics of 60° inclined dense jet in stagnant and wave environments. The wave environment is assumed to be a more realistic condition for marine discharges. Therefore, a new solver using AGFoam, which is a part of the ESI-OpenCFD package of OpenFOAM, was developed. New formulations were deployed for the estimation of k and ω at the inlet and outlet boundaries of the wave environment. The results were compared to the behavior of dense jets in the stagnant water. The comparisons demonstrated that wave motions lead to the oscillation of dense jet near the source and this oscillation in turn increases flow mixing and dilution up to the impact point. So it observed that in wave motions, pollutants spread faster and it changes flow width and geometry significantly.
•Desalination brine discharge in stagnant and wave environments was investigated.•Behavior of 60° inclined dense jets as the angle with maximum dilution was studied.•The results in each case were compared to previous experimental and numerical data.•The k-ω SST turbulence model was found conservative in the prediction of flow.
•First study to incorporate oscillating cylinder wake dynamics in reaction kinetics of two scalars.•Introduced RAvg (weighted area average reaction rate), a novel parameter, for detailed reaction ...rate analysis.•Established empirical relationships between reaction rate (RAvg) and cylinder motion amplitudes.•High-frequency regime sees an exponential increase in reaction rate with increasing amplitudes.•Low-frequency regime shows a linear decrease in reaction rate with increasing amplitudes.
This study investigates the effect of the wake generated by a circular cylinder undergoing transverse oscillations on the second-order reaction kinetics between two distant scalars. The cylinder's motion is characterized by frequency and amplitude, and the effects of different amplitude ratios (0.1, 0.25, 0.5, 0.75, and 1.0) are analyzed at fixed frequency regimes (0.1 and 0.5). To accurately characterize the phenomenon, a newly introduced parameter, RAvg (weighted area average of reaction rates), is used in conjunction with laterally integrated time-averaged reaction rates (R̂). A static cylinder is used as a baseline for comparison, and the study keeps the Reynolds number constant at 250 while fixing the Damkohler (0.01) and Schmidt (10) numbers. The study shows that RAvg increases exponentially with amplitude in the higher frequency regime but decreases linearly in the lower frequency regime. Additionally, R̂ increases monotonically in the streamwise direction for all frequency regimes and amplitude ratios. The results provide insights into the complex interactions between fluid dynamics and reaction kinetics, which have implications in fields such as chemical processes and environmental pollution, and energy production etc. Overall, this study highlights the importance of accurately characterizing these interactions and provides a new parameter for this purpose.
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Flame simulations with an open-source code Dasgupta, Adhiraj; Gonzalez-Juez, Esteban; Haworth, Daniel C.
Computer physics communications,
April 2019, 2019-04-00, Letnik:
237
Journal Article
Recenzirano
Flame simulations are used to gain insight into combustion physics and to design combustion systems such as piston engines, gas–turbine engines, and process heaters. In these simulations, the balance ...between reaction and molecular mixing plays a key role. To model molecular mixing, using a full multicomponent approach leads to high accuracy at the expense of a hefty computational cost. Thus, the use of a mixture-averaged model is usually preferred. Hence, this paper presents and tests a new OpenFOAM®-based code that incorporates a detailed, mixture-averaged approach for calculating transport properties in reacting flows, and provides a capability to solve either fully-compressible or low-Mach-number governing equations. The code is made readily available on GitHub and is written completely in OpenFOAM®’s native code framework, making it highly portable and easy to maintain, enhance, and extend. It is tested by modeling two laminar flames, and two turbulent flames undergoing extinction and reignition. Overall, predictions with the present code are seen to be in good agreement with experimental and direct-numerical-simulation data.
Program Title:laminarReactingFoam &laminarReactingLMFoam
Program Files doi:http://dx.doi.org/10.17632/h8hch3hs9p.1
Licensing provisions: GPLv3
Programming language: C++.
Nature of problem: In high-resolution flame simulations it is important to calculate the transport properties without using simplified models in order to capture the physics of the problem. Assumptions such as unity Lewis number do not always provide an accurate answer, and in some cases may not be able to capture some of the relevant physics.
Solution method: The present code adds the functionality to calculate the transport properties of the gas mixture using a detailed, mixture-averaged formulation.
Investigation of boiling in a square channel, which is filled partly with porous medium, is reported. Influence of major parameters such as porosity and extent of filling of the porous medium on heat ...transfer rate, vapour volume fraction, vapour generation rate and pressure drop are analyzed. A new solver utilizing the framework of open-source CFD code OpenFOAM is developed to investigate the problem. It is found that addition of porous medium increases fluid temperature, vapour volume fraction, heat transfer and vapour generation rate. It is also established that heat transfer increases on lowering the porosity of porous matrix, when the ratio of thickness of porous medium to channel height (Hp⁎) is greater than 0.4. In addition, heat transfer rate increases if the porosity increases for Hp⁎ < 0.4, but not significantly, as compared to the cases with Hp⁎ > 0.4. Moreover, there is an increase in pressure drop for an increase in thickness and a decrease in the porosity. It is also found that for two-phase heat transfer, the maximum Nusselt number is approximately 4.8 times higher than that for the single-phase heat transfer in the same channel.
Inertia-induced cross-stream migration has been recently exploited for precise position of particles in confined channel flows. In this work, a three-dimensional finite volume based immersed boundary ...method has been developed to study the lateral migration and hydrodynamic self-assembly of neutrally-buoyant particles in pressure-driven flows. Simulation results show that, in 2D channel flows, the equilibrium position for a circular particle is closer to the centreline for larger particle Reynolds number due to the increasing flow rate, while in 3D square duct flow, the equilibrium position for a spherical particle is near a face centre and is closer to the wall for larger particle Reynolds number. Self-assembly of a pair of particles is observed in 3D square duct flows but not in 2D channel flows. Mechanisms for the self-assembly are discussed.
