CFD study of Jet Impingement Test erosion using Ansys Fluent® and OpenFOAM®

The initial aim of this study was to compare OpenFoam and Ansys Fluent in order to verify OpenFoam’s Lagrangian Library and erosion capabilities. However, it was found that previous versions of Fluent have been providing wrong results for the discrete phase and the differences with the latest version (Ansys Fluent 15) are shown. A Submerged Jet Impingement Test is an effective method for studying erosion created by solid particles entrained in a liquid. When considering low particle concentrations a Lagrangian modeling of the particulate phase is a reasonable approach. Proper linkage between OpenFOAM’s Lagrangian library and the solver pimpleFoam for incompressible transient flows allows two-phase simulations to be undertaken for comparison with Ansys Fluent with the aim of verifying OpenFoam’s accuracy. Steady state convergence for the fluid flow is first accomplished and the results are compared, confirming a good agreement between the two packages. A transient simulation was then set up and spherical particles incorporated into the fluid flow. An assessment of the two codes’ discrete phase models was carried out, focusing on the differences between impact angles and velocities yielded at the impingement plate’s surface employing a similar strategy to that outlined first by Hattori et al. (2008) and later by Gnanavelu et al. (2009, 2011). In the comparison of OpenFoam with the latest version of Fluent, the main differences between the injection models are highlighted and the coupling possibilities between phases are taken into consideration. Agreement between trends for both impact angles and velocities is satisfactory when the last version of the commercial package is considered and the average discrepancy between numerical values is very low, verifying OpenFoam’s Lagrangian library. Two different Jet Impingement Test configurations are also compared and the differences highlighted

Computational fluid dynamics study of erosion processes

Previously held under moratorium from 7 December 2017 until 24 February 2022A very large number of papers have been published on erosion for over 50 years. For the first time, a series of geometry independent tools and methodologies have been developed to calculate erosion and its associated mesh deformation in any three dimensional domain. The software used for development is verified first against the literature and Ansys Fluent. An error was found in the implementation of the Lagrangian phase in Fluent which was corrected in a later version. It is suspected that the error affects a large number of CFD publications in which the Discrete Phase Model was used. An experimental methodology and test-rig that is able to erode samples at mass concentrations ranging from 1% to 7% were developed and repeatability confirmed through testing. Despite not being able to use the test-rig due to technical issues, erosion associated deformation was validated from the literature, confirming the appearance of a new stagnation area as the wear scar deepens in the Jet Impingement Test. The algorithm was also applied to centrifugal slurry pumps in combination with state of the art erosion modeling and its results validated through visual inspection of eroded models.A very large number of papers have been published on erosion for over 50 years. For the first time, a series of geometry independent tools and methodologies have been developed to calculate erosion and its associated mesh deformation in any three dimensional domain. The software used for development is verified first against the literature and Ansys Fluent. An error was found in the implementation of the Lagrangian phase in Fluent which was corrected in a later version. It is suspected that the error affects a large number of CFD publications in which the Discrete Phase Model was used. An experimental methodology and test-rig that is able to erode samples at mass concentrations ranging from 1% to 7% were developed and repeatability confirmed through testing. Despite not being able to use the test-rig due to technical issues, erosion associated deformation was validated from the literature, confirming the appearance of a new stagnation area as the wear scar deepens in the Jet Impingement Test. The algorithm was also applied to centrifugal slurry pumps in combination with state of the art erosion modeling and its results validated through visual inspection of eroded models

Liquid metal flows in continuous casting molds: A numerical study of electromagnetic flow control, turbulence and multiphase phenomena

Der Effekt eines externen Magnetfeldes auf die mehrphasige und turbulente Strömung in Stranggußkokillen und deren Wechelspiel führt in den wissenschaftlichen Arbeiten zu widersprüchlichen Aussagen. Die verschiedenen Prozessparameter können innerhalb eines kleinen Varianzbereichs entscheidenden Einfluss auf die Aussage haben, ob ein Magnetfeld begünstigend oder schädigend auf die Qualität des Produkts wirkt. Um wichtige Einflussfaktoren zu identifizieren, werden daher numerische Strömungssimulationen des Prozesses durchgeführt. Dazu wird zunächst ein mehrphasiger und inkompressibler Mehrregionen-CFD-Löser für magnetohydrodynamische Strömungen entwickelt und validiert, um die komplexe Strömung in einer Stranggußkokille mit hoher Genauigkeit simulieren zu können. Darauf aufbauend wird das numerische Setup anhand einer Modellkokille mit aktuellen Messdaten validiert. Durch die neuartige Kombination Lagrange'scher Lösungsmethoden mit angepassten Termen für die Magnetohydrodynamik sowie der skalenaufgelösten magnetohydrodynamischen Turbulenz, können erstmals Aussagen zur optimalen Magnetfeldverteilung im Hinblick auf Strömungsstabilität, Turbulenzmodulation und Blasenverteilung getroffen werden. Mit Hilfe dieses Wissens können neuartige Konzepte elektromagnetischer Bremssysteme für den Stranggußprozess entwickelt werden

Numerical Modeling of Suspension and Particle Transport in Thermal Spray Processes

Fine microstructured coatings have attracted many attentions in recent years due to various unique properties such as remarkable wear resistance, enhanced catalytic behavior, and superior thermal insulation. Suspension thermal sprays have been shown to be viable techniques in generating this kind of coatings. In these techniques, suspension which is a combination of a base liquid and fine solid particles is injected into a high-temperature high-velocity jets. After suspension breakup, the evaporation/combustion of base liquid becomes dominant. Then, the remained particles are accelerated and heated up by the gas flow and are deposited on a substrate which results in the generation of dense and well-adhered coatings. Suspension thermal spraying is very complex and many fields such as turbulent flow, multiphase flow, compressible flow, combustion, atomization, suspension properties, and plasma physics are involved in the mentioned technique. In addition, many parameters and mechanisms in this technique are still unknowns. Therefore, both numerical and experimental studies should be performed to obtain a comprehensive understanding of various phenomena in suspension thermal spraying and to improve the coating quality. The main goal of this study is the numerical modeling of suspension thermal sprays. An Eulerian-Lagrangian approach with two-way coupling assumption is presented and suspension droplet evolution in the atmospheric plasma spraying and high velocity oxygen fuel spraying techniques is investigated. In this model, suspension is considered as a multi-component mixture and a predefined droplet distribution is injected into the jet. In this approach, the breakup process is simulated using Taylor Analogy Breakup (TAB), and Kelvin-Helmholtz Rayleigh-Taylor (KHRT) breakup models. After breakup process is complete, the liquid component of suspension droplet evaporates/burns, and the particles/agglomerates are tracked in the domain. In general, the effects of suspension injection velocity, suspension properties, suspension injector location, standoff distance, substrate shape, and gas properties on the coating characteristics can be investigated by this approach. For example, in the case of radial injection of suspension into a plasma plume, it is illustrated that if particles move close to the jet centerline, particle velocity and temperature as well as probability of particle impact on the substrate will increase. The mentioned Eulerian-Lagrangian approach revealed that the breakup phenomenon mainly controls the droplets/particles trajectories, temperatures and velocities. However, the typical TAB and KHRT models ignore liquid/suspension column deformation, and need experimental calibration. To study the breakup process in more details, the effect of nonuniform gaseous crossflow and liquid column perturbations on the primary breakup of liquid jets are investigated. A coupled level set and volume-of-fluid method together with the large eddy simulation turbulence model are used to study the behavior of nonturbulent liquid jets in nonuniform crossflows. It is shown that liquid penetration height is significantly affected by the crossflow nonuniformity. In addition, to investigate the effects of liquid column perturbations on the breakup process, experimental studies are performed using shadowgraphy technique. General correlations for the penetration height, the column breakup point, and the onset of surface breakup are presented. It is found that the liquid column perturbations result in formation of large ligaments very close to the liquid and gas flows interaction point. These ligaments control the droplet size distribution and have significant effects on particle in-flight behavior, and coatings quality. The results of these studies can be used to estimate the spray trajectory in suspension plasma spray process, and to improve the accuracy of TAB and KHRT breakup models

Reconstruction and validation of arterial geometries for computational fluid dynamics using multiple temporal frames of 4D flow-MRI magnitude Images

Purpose Segmentation and reconstruction of arterial blood vessels is a fundamental step in the translation of computational fluid dynamics (CFD) to the clinical practice. Four-dimensional flow magnetic resonance imaging (4D Flow-MRI) can provide detailed information of blood flow but processing this information to elucidate the underlying anatomical structures is challenging. In this study, we present a novel approach to create high-contrast anatomical images from retrospective 4D Flow-MRI data. Methods For healthy and clinical cases, the 3D instantaneous velocities at multiple cardiac time steps were superimposed directly onto the 4D Flow-MRI magnitude images and combined into a single composite frame. This new Composite Phase-Contrast Magnetic Resonance Angiogram (CPC-MRA) resulted in enhanced and uniform contrast within the lumen. These images were subsequently segmented and reconstructed to generate 3D arterial models for CFD. Using the time-dependent, 3D incompressible Reynolds-averaged Navier–Stokes equations, the transient aortic haemodynamics was computed within a rigid wall model of patient geometries. Results Validation of these models against the gold standard CT-based approach showed no statistically significant inter-modality difference regarding vessel radius or curvature (p > 0.05), and a similar Dice Similarity Coefficient and Hausdorff Distance. CFD-derived near-wall hemodynamics indicated a significant inter-modality difference (p > 0.05), though these absolute errors were small. When compared to the in vivo data, CFD-derived velocities were qualitatively similar. Conclusion This proof-of-concept study demonstrated that functional 4D Flow-MRI information can be utilized to retrospectively generate anatomical information for CFD models in the absence of standard imaging datasets and intravenous contrast