1,720,979 research outputs found
A comparison of numerical methods for non-Newtonian fluid flows in a sudden expansion
No full textA numerical study on incompressible laminar flow in symmetric channel with sudden expansion is conducted. In this work, Newtonian and non-Newtonian fluids are considered, where non-Newtonian fluids are described by the power-law model. Three different computational methods are employed, namely a semi-implicit Chorin projection method (SICPM), an explicit algorithm based on fourth-order Runge-Kutta method (ERKM) and a Lattice Boltzmann method (LBM). The aim of the work is to investigate on the capabilities of the LBM for the solution of complex flows through the comparison with traditional computational methods. In the range of Reynolds number investigated, excellent agreement with the literature results is found. In particular, the LBM is found to be accurate in the prediction of the fluid flow behavior for the problem under consideration
Analysis of the fluid motion induced by a vibrating lamina through free surface-lattice boltzmann coupled method
No full textIn this work, we perform a numerical study on the flow induced by the motion of a rigid cantilever beam undergoing finite amplitude oscillations, in a viscous fluid, under a free surface. To this aim, we use a lattice Boltzmann volume of fluid (LB-VOF) integrated method, which includes the tracking of the fluid surface. The adopted approach couples the simplicity of the LB method with the possibility to track the free surface by means of a VOF strategy. Through a parametric analysis, we study the effects related to the depth of submergence, for several values of the oscillation frequency and amplitude. Results are provided in terms of a complex hydrodynamic function, whose real and imaginary parts are the added mass and the viscous damping, respectively, acting on the lamina. Validation of the results is carried out by comparing the solution, for the limit case of lamina submerged in an infinite fluid, with those from available literature studies. We find that the presence of the free surface strongly influences the flow physics around the lamina, especially at low values of the depth of submergence. In facts, when the lamina approaches to the free surface, the fluid waves, generated by the motion of the lamina, interact with the oscillating body itself, giving rise to additional effects, which we quantify in terms of added mass and viscous damping
Water impact on obstacles using KBC-free surface lattice Boltzmann method
No full textFree-surface flow problems represent an important class of problems in fluid dynamics. They occur in a wide range of applications and they involve many research fields, from naval architecture to civil and environmental engineering. Typical examples of free-surface problems are the wave impact on structures, breaking dams, hydraulic jumps, and many others. Such problems often involve complex geometries and transient regimes. These features, together with the need of tracking the motion of the free surface to properly predict the physical phenomena, make these problems particularly difficult to handle. Therefore, the capability of a computational model to accurately describe the dynamic characteristics of free-surface flows is nowadays extremely attractive. In this work, the breaking dam case with solid obstacle is simulated via a LB free-surface KBC approach. To date, no attempts have been made to simulate free-surface flows by adopting such collision model. This study demonstrates the viability of this approach, which was found to be stable and accurate in the prediction of the fluid flow phenomena under analysis
Numerical analysis of multiphase flows through the lattice boltzmann method
Full text linkQuesta tesi analizza il comportamento dei flussi multifase, nei quali ad esempio c’è la contemporanea presenza di diverse fasi fluide o di fase solida e fluida. Più specificatamente, in questo lavoro, i fluidi considerati sono fasi diverse della stessa sostanza, come ad esempio liquido e vapore. Una precisa definizione delle interazioni tra le molecole è di difficile formulazione. Ci sono molteplici fattori che sono sorgente di complessità nei flussi multifase, non solo l’interazione tra bolle/gocce/particelle immerse in un fluido, ma anche problemi fisici, come la transizione tra diversi regimi di flusso liguido-gas, o la presenza di interfacce perturbate, così come la simultanea presenza di fenomeni che si manifestano a diverse scale caratteristiche. Questa complessità rappresenta un limite piuttosto stringente all’utilizzo di metodi analitici sviluppati al fine di risolvere in forma chiusa questo tipo di problemi. Per le applicazioni più interessanti, riferiti a moderati numeri di Reynolds, manca una soluzione matematica chiusa.
Dopo aver evidenziato il grande vantaggio dell’analisi numerica di flussi multifase, è utile introdurre alcune applicazioni ingegneristiche. Alcuni esempi di flussi multifase sono spray (ad esempio nei Motori a Combustione Interna), oppure flussi nei tubi, letti fluidi, colonne di distillazione, etc. In aggiunta, ci sono diversi fenomeni “naturali” che coinvolgono flussi multifase come nuvole e pioggia, impatto di gocce liquide, onde, fiumi e cascate. Ancora, come anticipato in precedenza, le scale coinvolte nei flussi multifase coprono un ampio intervallo, partendo dai micrometri (spray) fino a raggiungere scale macroscopiche (kilometri). Questo enorme intervallo non permette la definizione di un modello universale per risolvere tutte queste applicazioni.
Partendo dalla semplicità dell’implementazione e maneggevolezza del metodo un sempre maggior numero di utilizzatori è stato incoraggiato ad utilizzare il Metodo Lattice Boltzmann al fine di ricostruire le equazioni fluidodinamiche. La grande diffusione è stata raggiunta soprattutto per modelli monofase. Ad ogni modo, diversi modelli sono stati definiti per questo approccio innovativo al fine di modellare le interazioni tra le diverse fasi. Il grande vantaggio nell’utilizzo di modelli multifase accoppiati con il Metodo Lattice Boltzmann è la possibilità di risolvere le equazioni di stato in ogni punto della griglia, con evidenti vantaggi intermini di accuratezza.
Quindi, lo scopo di questa tesi è di analizzare ed evidenziare quali sono le potenzialità di un innovativo modello multifase per LBM. Il modello proposto, basato sulla modellazione dell’energia libera, permette di raggiungere elevati livelli del rapporto tra le densità in relazione alle formulazioni tradizionalmente adottate. I risultati ottenuti in termini di break up primario e secondario, così come di coalescenza tra due gocce saranno approfonditamente analizzate. Nella parte finale del lavoro alcuni risultati per la formulazione tri-dimensionale saranno mostrati.This thesis deals with multiphase flows, i.e. systems in which different fluid phases, or fluid and solid phases, are simultaneously present. More specifically, in this work, the fluids are different phases of the same substance, such as a liquid and its vapor. A precise definition of interparticles’ interactions is difficult to formulate as, often, whether a certain situation should be considered as a multiphase flow problem depends more on the point of view of the investigator than on its intrinsic nature. There are a lot of factors which are source of complexity in the multiphase flow phenomena; not only the interaction between bubble/droplets/particles immersed in a fluid, but also physical problems, like the transition between different liquid-gas flow regimes, or the presence of a perturbed interface, as well the simultaneous presence of phenomena occurring at different scales. This complexity represents a tough limit in the use of fully analytical methods designed in order to solve this kind of problems. For the most interesting applications, referred to moderate Reynolds numbers, a closed analytical solution is missing.
After having pointed out the great advantage of multiphase flow numerical analysis, introducing some interesting engineering applications is useful. The multiphase problems, in fact, some examples are sprays (e.g. in Internal Combustion Engine -ICE-), or pipelines, fluidized bed, distillation columns, etc. Moreover there are many “Natural” phenomena which involve multiphase flows like clouds and rain, liquid droplets impingement, waves, rivers and water-falls. Again, as pointed out above, the scales involved in multiphase flows cover a complete range, starting from micro-meters (sprays) until reaching kilo-meters. This wide range does not allow defining a universal model capable to solve all these applications.
Due to the simplicity of implementation and managing a lot of users have been encouraged in using the Lattice Boltzmann Method –LBM in order to recast fluid-dynamic equations. The great diffusion has been reached concerning single-phase approach. However, many techniques have been defined for this innovative approach in order to model interactions between phases. The main advantage in using multiphase models coupled with the LBM is the possibility to solve the Equation of State -EOS- in every grid-point, with apparent advantages in terms of accuracy.
Thus, the aim of this work is to analyze and point out which are the capabilities for an innovative multiphase LBM approach. The proposed model, based on free energy modelling, allows to reach higher value for density ratio in comparison with standard formulations. The results obtained in terms of primary and secondary break-up, as well as coalescence between two droplets will be deeply described. In the final part of the work some results of the three-dimensional fully parallelized code will be shown
Experimental characterisation of a novel thermal energy storage based on open-cell copper foams immersed in organic phase change material
No full textA Coupled Lattice Boltzmann-Finite Volume Method for the Thermal Transient Analysis of an Air-Cooled Li-Ion Battery Module for Electric Vehicles with Porous Media Insert Modeled at REV Scales
No full textModern lattice Boltzmann methods for multiphase microflows
No full textDuring the last decade, the lattice Boltzmann (LB) method has captured an increasing attention as an efficient tool for the numerical simulation of complex fluids, particularly multiphase and multicomponent flows. In this paper, we revisit the basic features of two modern variants of LB models for non-ideal fluids, which offer promising perspectives for the numerical simulation of complex microflows. © 2011 The Author
Direct Numerical Simulation of an Open-Cell Metallic Foam through Lattice Boltzmann Method
No full textApplications of finite-difference lattice boltzmann method to breakup and coalescence in multiphase flows
No full text
- …
