1,721,044 research outputs found
Height function based Volume of Fluid code for simulations of multiphase magnetic fluids
No full textIn this work we develop, test and apply a height-function-based numerical code for the simulation of multiphase magnetic fluids. New hierarchical height function algorithms for interface normal and curvature (Bornia et al., 2011) are adapted and integrated into the Volume of Fluid component of our Navier-Stokes-Maxwell code for magnetic fluids and charge-free quasi-static magnetic fields. Accuracy and convergence results are presented for highly elongated ellipses characteristic of magnetic fluids, for static non-magnetic fluid droplets, and for magnetic fluid droplets elongated by an imposed uniform field. The code is applied to Magnetic Drug Targeting to demonstrate the response of magnetically controlled fluid regions to an imposed quadratic flow profile in a model vein
A Fluid-Structure Interaction Solver coupled to a Volume of Fluid method
No full textThe study of Fluid Structure Interaction (FSI) is becoming of great interest in many engineering applications. In this work we propose a new model to study the deformation of solid structures induced by a two-phase flow. We use a monolithic approach for the FSI problem while a Volume Of Fluid method (VOF) is considered for the reconstruction and advection of the interface. A PLIC method based on the ELVIRA algorithm for the reconstruction and a split algorithm for the interface advection is used. For an accurate reconstruction of the interface a huge number of computational elements are required and a multilevel algorithm coupled to an efficient compression-expansion technique is developed to reduce computational costs and memory requirements. An unstructured computational grid and a fine Cartesian mesh are used for the FSI and the VOF problem, respectively. The interaction between the two different grids is obtained by projecting the velocity field into the Cartesian grid and the Color function into the unstructured grid. This is performed with the MEDMEM libraries included in the Salome platform. The FSI problem is solved with a parallel multigrid C++ Finite Element code. Several test cases are presented
Numerical integration of implicit functions for the initialization of the VOF function
No full textA numerical method of initializing cell volume fraction demarcated by implicitly defined fluid interfaces is presented. Each cell of the computational domain is examined for the presence of the reference phase. When a cell is not full or empty, limits are found that allow volume fraction to be computed by numerical integration. The method enlists a number of algorithms including root finding and minimum search on an oriented segment, a preconditioned conjugate gradient minimum search on a cell face and a double Gauss–Legendre integration with a variable number of nodes, among others. Practical multi-phase fluid examples in two- and three-dimensions are presented to demonstrate the accuracy and robustness of the method
68th Annual Meeting of the APS Division of Fluid Dynamics, V0051: Primary breakup of planar coflowing gas and liquid sheets
No full textPrimary breakup of coflowing gas and liquid sheets is an important fluid dynamics problem which can been seen in many industrial applications like fuel injection. A solid understanding of spray formation through fuel injection systems is vital to improve the energy utilization efficiency and pollution control. In the present work, large-scale three-dimensional simulations are performed to investigate the breakup of coflowing gas and liquid sheets, using 2,048 processors on the supercomputer. The simulation results reveal the complex multi-scale multiphase flow features that are originally unclear. The detailed formation of the droplets through the breakup of the liquid sheet can be clearly seen from the video
Numerical validation of a κ-ω-κ θ -ω θ heat transfer turbulence model for heavy liquid metals
Full text linkpeer reviewedThe correct prediction of heat transfer in turbulent flows is relevant in almost all industrial applications but many of the heat transfer models available in literature are validated only for ordinary fluids with Pr ≃ 1. In commercial Computational Fluid Dynamics codes only turbulence models with a constant turbulent Prandtl number of 0.85 — 0.9 are usually implemented but in heavy liquid metals with low Prandtl numbers it is well known that these models fail to reproduce correlations based on experimental data. In these fluids heat transfer is mainly due to molecular diffusion and the time scales of temperature and velocity fields are rather different, so simple turbulence models based on similarity between temperature and velocity cannot reproduce experimental correlations. In order to reproduce experimental results and Direct Numerical Simulation data obtained for fluids with Pr ≃ 0.025 we introduce a κ-ε-κ θ -ε θ turbulence model. This model, however, shows some numerical instabilities mainly due to the strong coupling between κ and ε on the walls. In order to fix this problem we reformulate the model into a new four parameter κ-ω-κ θ -ω θ where the dissipation rate on the wall is completely independent on the fluctuations. The model improves numerical stability and convergence. Numerical simulations in plane and channel geometries are reported and compared with experimental, Direct Numerical Simulation results and with results obtained with the κ-ε formulation, in order to show the model capabilities and validate the improved κ-ω model
I dati metereologici per applicazioni energetiche e ambientali
No full textMany energetic and environmental evaluations need appropriate meteorological data, as input to analysis and prevision softwares.
In Italy there aren't adeguate meteorological data because, in many cases, they are incomplete, incorrect and also very expensive for a long-term analysis (that needs multi-year data sets).
A possible solution to this problem is the use of a Typical Meteorological Year (TRY), generated for specific applications. Nowadays the TRYs have been created, using statistical criteria, just for the analysis of solar energy systems and for predicting the thermal performance of buildings, applying it also to the study of photovoltaic plants (PV), though not specifically created for this type of application.
The present research has defined the methodology for the creation of TRYs for different applications. In particular TRYs for environmental and wind plant analysis have been created. This is the innovative aspect of this research, never explored before. In additions, the methodology of the generation for the PV TRYs has been improved.
The results are very good and the TRYs generated for these applications are adeguate to characterize the climatic condition of the place over a long period and can be used for energetic and environmental studies
Termofluidodinamica di un Getto di Litio
No full textCalcolo della superficie curvilinea di scorrimento di un getto di litio in maniera che la pressione lungo il getto vari in maniera lineare. Formulazione di un codice di calcolo per la determinazione delle diverse possibili superfici. Studio termofluidodinamico del getto con codici CFD. Accoppiamento tra codici di sistema e codici CFD. Valutazioni delle condizioni di Incipient Boiling per il litio
Multilevel Domain Decomposition Algorithms for Monolithic Fluid-Structure Interaction Problems with Application to Haemodynamics
No full textFinite element techniques for solving the problem of fluid-structure interaction of an elastic solid material in a laminar incompressible viscous flow are described. The mathematical problem consists of the Navier-Stokes equations in the Arbitrary Lagrangian-Eulerian formulation coupled with a non-linear structure model, considering the problem as one continuum. The coupling between the structure
and the fluid is enforced inside a monolithic framework which computes simultaneously for the fluid and the structure unknowns within a unique solver. We used the well-known Crouzeix-Raviart finite element pair for discretization in space and the method of lines for discretization in time. A stability result using the Backward-Euler time-stepping scheme for both fluid and solid part and the finite element method for the space discretization has been proved. The resulting linear system has been solved by multilevel domain decomposition techniques. Our strategy is to solve several local subproblems over subdomain patches using the Schur-complement or GMRES smoother within a multigrid iterative solver.
For validation and evaluation of the accuracy of the proposed methodology, we present corresponding results for a set of two FSI benchmark configurations which describe the self-induced elastic deformation of a beam attached to a cylinder in a laminar channel flow, allowing stationary as well as periodically oscillating deformations, and for a benchmark proposed by COMSOL multiphysics where a narrow vertical structure attached to the bottom wall of a channel bends under the force due to both viscous drag and pressure.
Then, as an example of fluid-structure interaction in biomedical problems, we considered the academic numerical test which consists in simulating the pressure wave
propagation through a straight compliant vessel.
All the tests show the applicability and the numerical efficiency of our approach to both two-dimensional and three-dimensional problems
A three-dimensional fem solver of the navier-stokes equations with applications to two-phase flows and innovative nuclear reactor concepts
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