Development Of Computational Fluid Dynamics Model Research Articles

Tool-pin profile effects on thermal and material flow in friction stir butt welding of AA2219-T87 plates: computational fluid dynamics model development and study

Tool-pin profile effects on thermal and material flow in friction stir butt welding of AA2219-T87 plates: computational fluid dynamics model development and study

CFD Modeling and Experimental Validation of the Flow Processes of an External Gear Pump

This article presents computational fluid dynamics (CFD) modeling of the flow processes at a certain specimen of an external gear pump. The purpose of the developed two-dimensional (2D) CFD model is to carry out a numerical study to obtain the main characteristics of the pump flow rate, especially the flow rate as a function of the pressure and the flow rate as a function of the time. A numerical study was carried out at forty-two different operating modes that were expressed as a variation of two parameters: rotational frequency (950–1450 min−1) and pressure (5–150 bar). The validation of the numerical results was carried out through an experimental study. For this purpose, a laboratory experimental setup equipped with a modern data acquisition (DAQ) system was designed and implemented. It allows the gear pump to be tested at the same operating modes as the numerical study. A validation analysis was performed by comparing the numerical and experimental results using the average relative error index (FIT). A detailed description of the 2D CFD model development (CAD model, mesh, general settings, boundary conditions, etc.) is provided. Based on the 2D CFD model, an original methodology was proposed to take into account the influence of the discharge channels on the displacement volume of the pump by adjusting the face width of the gears. Despite the limitations of the simple 2D CFD model, which are discussed in this article, a very good match between numerical and experimental results is analyzed by calculating the FIT level, which is in the range of 93–97%.

Computational Fluid Dynamics Modeling of Argon–Steel (–Slag) Multiphase Flow in an Ruhrstahl–Heraeus Degasser: A Review of Past Numerical Studies

Many metallurgical functions such as dehydrogenation, decarburization, and inclusion removal are achieved during Ruhrstahl–Heraeus (RH) treatment. The realization of these functions is closely related to argon–steel–slag flow in an RH degasser. Recently, computational fluid dynamics (CFD) methods have been widely adopted to understand such multiphase flow. This review summarizes and analyzes CFD modeling of argon–steel (–slag) flow from the aspect of fundamentals of the numerical approach, focusing on CFD models and validation (homogeneous fluid model, volume of fluid–discrete phase model, and Eulerian model), bubble behaviors (deformation, expansion, coalescence, and breakup), interfacial closure laws (drag, turbulent dispersion, lift, virtual mass, and wall lubrication forces), and turbulence closures (Reynolds‐averaged approach with standard, renormalization group, and realizable k–ε models, and large eddy simulation with Smagorinsky–Lilly model). This review also suggests that future challenge is to further develop a model for coupling the dispersed interface with a wide bubble size distribution and the sharp interface with a large interfacial scale, accompanied by appropriate bubble behaviors and general closure laws of interfacial forces. As a precondition for the development of CFD models, more experiments are required to fully understand the multiphase flow in a real RH degasser.

Simulation of Scrap Melting Process in an AC Electric Arc Furnace: CFD Model Development and Experimental Validation

The electric arc furnace (EAF) is a critical steelmaking facility that melts the scrap by the heat produced from electric arc and burners. Simulation and optimization of EAF scrap melting are of great interest to the steel industry, which helps to improve product quality and production efficiency. However, the relevant computational fluid dynamics (CFD) modeling of this process has not been reported so far. The present study established a three-dimensional (3D) integrated CFD model to simulate the scrap melting process in the alternating current (AC) EAF. The scrap melting model was developed to simulate the dynamic scrap melting and collapse based on the dual-cell approach and the stack approach. The electric arc model and the coherent jet model were introduced and integrated with the scrap melting model to estimate the electrical and chemical energy inputs need for melting. The CFD-compatible Monte Carlo method and electrode regulation strategy were developed respectively to predict the arc radiative heat dissipation and track the instant electrode movement. The experiments for the scrap melting by both electric arc and coherent jet burner were designed and implemented in the industry-scale NLMK 150-ton EAF for the model validation. The proposed model was applied to simulate the scrap melting process under the NLMK EAF typical run, and the scrap melting behavior, the electric arc performance, and the burner performance were evaluated and discussed based on the simulation results.

Synthesis of a CFD Benchmark Exercise: Examining Fluid Flow and Residence-Time Distribution in a Water Model of Tundish.

Computational Fluid Dynamics (CFD) has become an indispensable tool that can potentially predict many phenomena of practical interest in the tundish. Model verification and validation (V&V) are essential parts of a CFD model development process if the models are to be used with sufficient confidence in real industrial tundish applications. The crucial aspects of CFD simulations in the tundish are addressed in this study, such as the selection of the turbulence models, meshing, boundary conditions, and selection of discretization schemes. A series of CFD benchmarking exercises are presented serving as selected examples of appropriate modelling strategies. A tundish database, initiated by German Steel Institute VDEH working group “Fluid Mechanics and Fluid Simulation”, was revisited with the aim of establishing a comprehensive set of best practice guidelines (BPG) in CFD simulations for tundish applications. These CFD benchmark exercises yield important results for the sensible application of CFD models and contribute to further improving the reliability of CFD applications in metallurgical reactors.

Boundary-Condition Analysis of an Idealized Left Atrium Model.

The most common type of cardiac arrhythmia is atrial fibrillation (AF), which is characterised by irregular and ineffective atrial contraction. This behaviour results into the formation of thrombi, mainly in the left atrial appendage (LAA), responsible for thromboembolic events. Very different approaches are considered as therapy for AF patients. Therefore, it is necessary to yield insight into the flow physics of thrombi formation to determine which is the most appropriate strategy in each case. Computational Fluid Dynamics (CFD) has proven successful in getting a better understanding of the thrombosis phenomenon, but it still requires validation by means of accurate flow field in vivo atrial measurements. As an alternative, in this paper it is proposed an in vitro flow validation, consisting in an idealised model that captures the main flow features observed in the human LA which, once combined with Particle Image Velocimetry (PIV) measurements, provides readily accessible, easy to emulate, detailed velocity fields. These results have been used to validate our laminar and Large Eddy Simulation (LES) simulations. Besides, we have run a parametric study of different boundary conditions sets previously employed in the literature. These data can be used as a benchmark for further development of LA CFD models.

Thermal comfort prediction of air-conditioned and passively cooled engineering testing centres in a higher educational institution using CFD

PurposeThe purpose of this paper is to analyse the thermal environment of two engineering testing centres cooled via different means using computational fluid dynamics (CFD), focussing on the indoor temperature and air movement. This computational technique has been used in the analysis of thermal environment in buildings where the profiles of thermal comfort parameters, such as air temperature and velocity, are studied.Design/methodology/approachA pilot survey was conducted at two engineering testing centres – a passively cooled workshop and an air-conditioned laboratory. Electronic sensors were used in addition to building design documentation to collect the required information for the CFD model–based prediction of air temperature and velocity distribution patterns for the laboratory and workshop. In the models, both laboratory and workshop were presumed to be fully occupied. The predictions were then compared to empirical data that were obtained from field measurements. Operative temperature and predicted mean vote (PMV)–predicted percentage dissatisfied (PPD) indices were calculated in each case in order to predict thermal comfort levels.FindingsThe simulated results indicated that the mean air temperatures of 21.5°C and 32.4°C in the laboratory and workshop, respectively, were in excess of the recommended thermal comfort ranges specified in MS1525, a local energy efficiency guideline for non-residential buildings. However, air velocities above 0.3 m/s were predicted in the two testing facilities, which would be acceptable to most occupants. Based on the calculated PMV derived from the CFD predictions, the thermal sensation of users of the air-conditioned laboratory was predicted as −1.7 where a “slightly cool” thermal experience would prevail, but machinery operators in the workshop would find their thermal environment too warm with an overall sensation score of 2.4. A comparison of the simulated and empirical results showed that the air temperatures were in good agreement with a percentage of difference below 2%. However, the level of correlation was not replicated for the air velocity results, owing to uncertainties in the selected boundary conditions, which was due to limitations in the measuring instrumentation used.Research limitations/implicationsDue to the varying designs, the simulated results of this study are only applicable to laboratory and workshop facilities located in the tropics.Practical implicationsThe results of this study will enable building services and air-conditioning engineers, especially those who are in charge of the air-conditioning and mechanical ventilation (ACMV) system design and maintenance to have a better understanding of the thermal environment and comfort conditions in the testing facilities, leading to a more effective technical and managerial planning for an optimised thermal comfort management. The method of this work can be extended to the development of CFD models for other testing facilities in educational institutions.Social implicationsThe findings of this work are particularly useful for both industry and academia as the indoor environment of real engineering testing facilities were simulated and analysed. Students and staff in the higher educational institutions would benefit from the improved thermal comfort conditions in these facilities.Originality/valueFor the time being, CFD studies have been carried out to evaluate thermal comfort conditions in various building spaces. However, the information of thermal comfort in the engineering testing centres, of particular those in the hot–humid region are scantily available. The outcomes of this simulation work showed the usefulness of CFD in assisting the management of such facilities not only in the design of efficient ACMV systems but also in enhancing indoor thermal comfort.

Novel trends in modelling techniques of Pelton Turbine bucket for increased renewable energy production

Pelton turbines have been used for harvesting clean energy from water jet for over 100 years. The wide range of their applicability and the robustness with minimal onsite monitoring and carbon free energy production makes them one of the most desired hydro turbines for renewable energy production. Pelton turbine buckets are subject to complex turbulent multiphase flows with free surfaces, thus received lot of attention from Computational Fluid Dynamics (CFD) researchers to visualise the flow patterns. In addition, the bucket geometry optimization has been a prevalent research stream using analytical and graphical methods. Both of these investigations fields have resulted in significant improvement in the performance of the Pelton Turbine system. However, the design investigations for each feature are carried out independently due to the complexity in incorporating large number of design parameters. Thus, analysing the complex fluid flow on each pre-optimized design was rather challenging due to expensive computational needs of CFD and limited manufacturing possibilities. Today, development of accurate and inexpensive CFD models and innovative manufacturing technology such as rapid prototyping has made complex freeform shape possible to simulate and manufacture. Hence, any bucket designs disregarded in optimization on the basis of manufacturing feasibility can now be possible to manufacture and is worth investigating. This will require the combination of CFD and design optimization field of investigation with novel analysis approach. This paper examines these fields of studies with the view to establish the background for such novel approach. This approach could be a foundation for design optimization of turbomachinery or any reaction surface leading to increased production of renewable and sustainable energy from existing resources.

CFD simulation of the transient gas transport in a PEM fuel cell cathode during AC impedance testing considering liquid water effects

This work presents the application of CFD (Computational Fluid Dynamics) to the unsteady gas transport modelling in the cathode side of a Polymer Electrolyte Membrane (PEM) fuel cell during an AC impedance test. The CFD model development and results during AC impedance experiments for 1D and 2D cases are presented and discussed. The effect of liquid water was considered by modelling scenarios with saturated (according to water profiles obtained experimentally) and dry Gas Diffusion Layers (GDL). It was observed that the magnitude of the transient variations of the oxygen concentration within the GDL is dependent on the frequency of the AC signal during the test, given the differences between the diffusion characteristic time and the oxygen consumption characteristic time. For the 2D model where the differences under-the-rib to under-the-channel can be analysed, it was verified that oxygen concentration is much higher under the channel, however the amplitude of the oscillations during AC testing are significantly higher under the rib. When comparing saturated and dry GDLs for both models, it was verified that oxygen concentrations are higher for dry GDLs, but the amplitude of the oscillations is however higher for saturated GDLs.

CFD model simulation of bubble surface area flux in flotation column reactor in presence of minerals

Bubble surface area flux (Sb) is one of the main design parameter in flotation column that typically employed to describe the gas dispersion properties, and it has a strong correlation with the flotation rate constant. There is a limited information available in the literature regarding the effect of particle type, density, wettability and concentration on Sb. In this paper, computational fluid dynamics (CFD) simulations are performed to study the gas–liquid–solid three-phase flow dynamics in flotation column by employing the Eulerian–Eulerian formulation with k-ε turbulence model. The model is developed by writing Fortran subroutine and incorporating then into the commercial CFD code AVL FIRE, v.2014. This paper studies the effects of superficial gas velocities and particle type, density, wettability and concentration on Sb and bubble concentration in the flotation column. The model has been validated against published experimental data. It was found that the CFD model was able to predict, where the response variable as indicated by R-Square value of 0.98. These results suggest that the developed CFD model is reasonable to describe the flotation column reactor. From the CFD results, it is also found that Sb decreased with increasing solid concentration and hydrophobicity, but increased with increasing superficial gas velocity. For example, approximately 28% reduction in the surface area flux is observed when coal concentration is increased from 0 to 10%, by volume. While for the same solid concentration and gas flow rate, the bubble surface area flux is approximately increased by 7% in the presences of sphalerite. A possible explanation for this might be that increasing solid concentration and hydrophobicity promotes the bubble coalescence rate leading to the increase in bubble size. Also, it was found that the bubble concentration would decrease with addition of hydrophobic particle (i.e., coal). For instance, under the same operating conditions, approximately 23% reduction in the bubble concentration is predicted when the system was working with hydrophobic particles. The results presented are useful for understanding flow dynamics of three-phase system and provide a basis for further development of CFD model for flotation column.

Surrogate-based model parameter optimization based on gas explosion experimental data

ABSTRACTThis article presents a method for optimizing the predictive capabilities of a computational fluid dynamics (CFD) tool used for consequence analysis in the process industries. A procedure for surrogate-based optimization of empirically determined sub-grid model parameters is implemented. The objective is to yield the best fit between certain outputs of a CFD model and corresponding experimental values. The present study investigates whether the optimization approach is applicable for improving the predictions of gas explosions when optimizing (i) only for experiments involving similar physical phenomena and (ii) for a wider range of experiments including symmetric modules as well as realistic offshore modules. Employing optimization may detect model limitations, supporting the further development of complex CFD models to represent a wider range of physical phenomena. The optimization process significantly improves the prediction of the maximum overpressure and pressure impulse at specific monitor points. Online supplemental data for this article can be accessed athttps://doi.org/10.1080/0305215X.2018.1450399.

Computational Fluid Dynamics Modeling of Temperature Distribution in Fluidized Bed Polymerization Reactor for Polypropylene Production

Propylene polymerization process is one of the chemical processes that take place in the fluidized bed reactor. The gas monomer is fed through the distributor to react with the solid catalyst particles inside the reactor. The polymer particles are produced from the heterogeneous exothermic polymerization reaction. Although the fluidized bed polymerization reactor has high heat and mass transfer rate, the thermal efficiency is usually limited due to the formation of hot spots and improper mixing. In this research, a computational fluid dynamics (CFD) model of the fluidized bed polymerization reactor for polypropylene production is developed in order to study the temperature distribution within the reactor. The polymer growth rate and particle size distribution are included in the CFD model development. The heat is generated from highly exothermic polymerization reaction and removed in the heat exchanger. By proper adjusting the monomer feed velocity, the uniform temperature distribution inside the reactor is obtained in axial and radial directions. Additionally, the temperature of the outlet gas stream can be reduced, thus reducing the external cooling duty.

Simulation benchmark based on THAI-experiment on dissolution of a steam stratification by natural convection

Locally enriched hydrogen as in stratification may contribute to early containment failure in the course of severe nuclear reactor accidents. During accident sequences steam might accumulate as well to stratifications which can directly influence the distribution and ignitability of hydrogen mixtures in containments. An international code benchmark including Computational Fluid Dynamics (CFD) and Lumped Parameter (LP) codes was conducted in the frame of the German THAI program. Basis for the benchmark was experiment TH24.3 which investigates the dissolution of a steam layer subject to natural convection in the steam-air atmosphere of the THAI vessel. The test provides validation data for the development of CFD and LP models to simulate the atmosphere in the containment of a nuclear reactor installation. In test TH24.3 saturated steam is injected into the upper third of the vessel forming a stratification layer which is then mixed by a superposed thermal convection. In this paper the simulation benchmark will be evaluated in addition to the general discussion about the experimental transient of test TH24.3. Concerning the steam stratification build-up and dilution of the stratification, the numerical programs showed very different results during the blind evaluation phase, but improved noticeable during open simulation phase.

Simulations and Experiments to Reach Numerical Multiphase Informations for Security Analysis on Large Volume Vacuum Systems Like Tokamaks

Dust re-suspension as a consequences of loss of vacuum accident (LOVA) or loss of coolant accident (LOCA) situations inside a nuclear fusion plant (ITER-like) is an important issue for the workers’ safety and for the security of the plant. The dust size expected inside tokamaks like ITER is of the order of microns (0.1–1000 μm). Analysis of the thermo fluid-dynamics and transport phenomena involved during an accidental pressurization transitory is necessary in order to set up and operated tokamaks with careful consideration of the potential risks. Computational fluid dynamics (CFD) study of LOVA scenario is a challenging task for today numerical methods and models because it involves 3D large vacuum volumes, multiphase flows ranging from highly supersonic to nearly incompressible and heat transfer simultaneously. Present work deals with development and experimental validation of CFD model, which simulates the complex thermo fluid-dynamic field and gives some indication about internal hazardous dust mobilization phenomena during vessel filling at near vacuum conditions, for supporting first instant of LOVA safety analysis. The research activity had been carried out in the framework of EURATOM–ENEA Association—University of Rome Tor Vergata Quantum Electronics Plasma Physics and Materials Research Group.

DNS of turbulent flow with hemispherical wall roughness

The present study of the effect of roughness density on the mean flow turbulence parameters is motivated by the need for new generation of boundary conditions for multiphase computational multiphase fluid dynamics (CMFD) models applied to boiling flows. Effect of roughness element density on the turbulent flow in a channel is quantified through direct numerical simulations (DNSs). The Navier--Stokes equations are solved using finite element method and bubbles are approximated as rigid near-hemispherical obstacles at the wall. Six different cases were analysed including channel flow with smooth wall and channel flow with rough wall for five different bubble nucleation site densities. Friction factor and the law of the wall was calculated and compared with the previously published results. Existing correlations for nucleating bubble site density dependency on a wall heat flux were used to obtain a relation between the heat flux and the friction factor, leading to the law of the wall dependency on the heat flux. This separate effect study provides new guidelines on how the heat flux in subcooled boiling regime affects the turbulence behaviour near the wall and guides the computational fluid dynamics model development for boiling two-phase flows.

Gas-particle Flow Modeling: Beyond the Dilute Limit

The flow of pulverized fuel in a power plant is one example of gas-particle flows in the energy and process industries. Computational Fluid Dynamics (CFD) is a widely used trouble shooting and engineering design tool increasingly deployed within industry to predict the behavior of such flows. Despite wide use, traditional models are often inadequate for solving industrial problems. An example is the concentration of the particulate phase within a coal burner's fuel feed due to particle inertia and inter-particle collisions. This local concentration of the particles can be advantageous, but it is difficult to characterize the flow beyond the dilute limit (volume fraction of 0.001). To address this and other short comings a number of two-phase flow models have been investigated and their applicability and accuracy assessed by comparison with experiments in the literature for a vertical pipe flow with relatively high mass loadings of the discrete phase. The physics investigated includes: particle-wall collisions, particle-particle collisions and structure dependent drag. Models have been implemented in the commercial CFD software ANSYS FLUENT R.14.5 for the Discrete Phase Model. The results show a significant improvement over industry best practice and provide an indication as to the key physics and the effects of scale on confined gas-particle flows. Furthermore, the modeling approach will be applicable in a number of other industrial areas, such as biomass conveying. This paper provides an overview of CFD models for the application to pulverized fuel flows within a coal fired power plant and discusses the gap between academic development and industrial adoption of advanced CFD models.

Quasi One-Dimensional Model of Natural Draft Wet-Cooling Tower Flow, Heat and Mass Transfer

The article deals with the development of CFD (Computational Fluid Dynamics) model of natural draft wet-cooling tower flow, heat and mass transfer. The moist air flow is described by the system of conservation laws along with additional equations. Moist air is assumed to be homogeneous mixture of dry air and water vapour. Liquid phase in the fill zone is described by the system of ordinary differential equations. Boundary value problem for the system of conservation laws is discretized in space using Kurganov-Tadmor central scheme and in time using strong stability preserving Runge-Kutta scheme. Initial value problems in the fill zone is solved by using standard fourth order Runge-Kutta scheme. The interaction between liquid water and moist air is done by source terms in governing equations.

Towards a more sustainable transport sector by numerically simulating fuel spray and pollutant formation in diesel engines

Diesel engines account for approximately 50% of new passenger-car sales in the European market and are the major contributor to pollutants that adversely affect human health and the environment. The most adverse pollutants emitted by the combustion of diesel fuel are NOx, soot, CO and HC. Numerous studies have been carried out to determine the influence of engine design, fuel injection, fuel-air mixing and combustion on pollutant emissions. Information gained through experimental research of in–cylinder processes is limited, and the body of knowledge can be improved by the use of numerical modelling and computer simulations. Computational Fluid Dynamics (CFD) has become a valuable tool that decreases the time and the cost of experimental research. Therefore, CFD is being increasingly used in development of combustion systems. This paper presents how the development of CFD models is the proper approach towards achieving a cleaner and more sustainable transportation sector. The physical models for the liquid fuel disintegration, evaporation and pollutant formation are used and implemented into the commercial CFD code FIRE. The models are capable of predicting complex in–cylinder processes and, ultimately, the formation of pollutant emissions. The results from numerical simulations, such as NOx and soot concentrations, in–cylinder pressure and temperature are found to be in good agreement with the existing experimental data.

Implementation of CFD modeling in the performance assessment and optimization of secondary clarifiers: the PVSC case study

The water industry and especially the wastewater treatment sector has come under steadily increasing pressure to optimize their existing and new facilities to meet their discharge limits and reduce overall cost. Gravity separation of solids, producing clarified overflow and thickened solids underflow has long been one of the principal separation processes used in treating secondary effluent. Final settling tanks (FSTs) are a central link in the treatment process and often times act as the limiting step to the maximum solids handling capacity when high throughput requirements need to be met. The Passaic Valley Sewerage Commission (PVSC) is interested in using a computational fluid dynamics (CFD) modeling approach to explore any further FST retrofit alternatives to sustain significantly higher plant influent flows, especially under wet weather conditions. In detail there is an interest in modifying and/or upgrading/optimizing the existing FSTs to handle flows in the range of 280-720 million gallons per day (MGD) (12.25-31.55 m(3)/s) in compliance with the plant's effluent discharge limits for total suspended solids (TSS). The CFD model development for this specific plant will be discussed, 2D and 3D simulation results will be presented and initial results of a sensitivity study between two FST effluent weir structure designs will be reviewed at a flow of 550 MGD (∼24 m(3)/s) and 1,800 mg/L MLSS (mixed liquor suspended solids). The latter will provide useful information in determining whether the existing retrofit of one of the FSTs would enable compliance under wet weather conditions and warrants further consideration for implementing it in the remaining FSTs.

Computational fluid dynamics model development on transport phenomena coupling with reactions in intermediate temperature solid oxide fuel cells

A 3D model is developed to describe an anode-supported planar solid oxide fuel cell (SOFC), by Ansys/Fluent evaluating reactions including methane steam reforming (MSR)/water-gas shift (WGSR) reactions in thick anode layer and H2-O2/CO-O2 electrochemical reactions in anode active layer, coupled with heat, mass species, momentum, and ion/electron charges transport processes in SOFC. The predicted results indicate that electron/ion exchange appears in the very thin region in active layers (0.018 mm in anode and 0.01 mm in cathode), based on three phase boundary, operating temperature and concentration of reactants (mainly H2). Active polarization happening in active layers dominates over concentration and ohmic losses. High gradient of current density exists near interface between electrode and solid conductor due to the block by gas channel. It is also found the reaction rates of MSR and WGSR along main flow direction and cell thickness direction decrease due to low concentration of fuel (CH4) caused by mass consumption. With increasing operating temperature from 978 K to 1088 K, the current density and the reaction rate of MSR are increased by 10.8% and 5.4%, respectively. While ion current density is 52.9% higher than in standard case, and H2 is consumed by 5.1% more when ion conductivity is doubled. CO-O2 has been considered in charge transfer reaction in anode active layer and it is found that the current density and species distributions are not sensitive, but WGSR reaction will be forced backwards to supply more CO for CO-O2 electrochemical reaction.