NOWADAYS, a number of studies keep on demonstrating the existence of a strong relation between high concentrations of particulate matter (PM) and the prevalence of human morbidity and mortality. Large particles can be filtered in the nose or in the throat, while fine particles (about10 micrometer) can settle in the bronchi and lungs, leading to more serious consequences. According to Karagulian et al. the major sources of urban air pollution are traffic (25%), combustion and agriculture (22%), domestic fuel burning (20%), natural dust (18%) and industrial activities (15%).As a consequence, the detailed study of dispersion phenomena within the urban canopy becomes a target of great interest. To this end, Computational Fluid Dynamics (CFD) can be successfully employed to predict turbulence and dispersion patterns, accounting for a detailed characterization of the pollutant sources, complex obstacles and atmospheric stability classes.Despite being intrinsically different phenomena, turbulence and dispersion are closely related. It is universally accepted that, to reach accurate prediction of the concentration field, it is necessary to properly reproduce the turbulence one. For this reason, the present PhD thesis is split into two main Sections: one focused on turbulence modelling and the subsequent, centered on the dispersion modelling.Thanks to its good compromise between accuracy of results and calculation time, Reynolds-averaged Navier-Stokes (RANS) still represents a valid alternative to more resource-demanding methods. However, focusing on the models’ performance in urban studies, Large Eddy Simulation (LES) generally outperforms RANS results, even if the former is at least one order of magnitude more expensive. Stemming from this consideration, the aim of this work is to propose a variety of approaches meant to solve some of the major limitations linked to standard RANS simulation and to further improve its accuracy in disturbed flow fields, without renouncing to its intrinsic feasibility. The proposed models are suitable for the urban context, being capable of automatically switching from a formulation proper for undisturbed flow fields to one suitable for disturbed areas. For neutral homogeneous atmospheric boundary layer (ABL), a comprehensive approach is adopted, solving the issue of the erroneous stream-wise gradients affecting the turbulent profiles and able to correctly represent the various roughness elements. Around obstacles, more performing closures are employed. The transition between the two treatments is achieved through the definition of a Building Influence Area (BIA). The finalgoal is to offer more affordable alternatives to LES simulations without sacrificing a good grade of accuracy.Focusing on the dispersion modelling framework, there exists a number of parameters which have to be properly specified. In particular, the definition of the turbulent Schmidt number Sct, expressing the ratio of turbulent viscosity to turbulent mass diffusivity, is imperative. Despite its relevance, the literature does not report a clear guideline on the definition of this quantity. Nevertheless, the importance of Sct with respect to dispersion is undoubted and further demonstrated in the works of different authors. For atmospheric boundary layer flows, typical constant values range between 0.2 and 1.3. As a matter of fact, the local variability of Sct is supported by experimental evidence and by direct numerical simulations (DNS). These observations further suggest that the turbulent Schmidt number should be prescribed as a dynamic variable. Following these observations a variable turbulent Schmidt number formulation is proposed in this work. The latter stems from the same hypothesis of the variable formulation developed by Gorlé et al. Moreover, the relevant uncertain model parameters are optimized through uncertainty quantification (UQ). This formulation further increased the accuracy of the predictions, and was successfully verified by Di Bernardino et al. However, the turbulent Schmidt number resulting from this formulation is still intrinsically linked to the turbulence model employed, i.e. to the Cμ coefficient. To overcome this constraint, the nature and the dependencies of Sct were further analyzed through correlation studies and employing principal component analysis (PCA) on data obtained through the proposed ABL RANS model. Subsequently, the same data-driven technique was employed based on the high-fidelity outcomes of a delayed Detached Eddy Simulation (dDES) to derive a generalized turbulentSchmidt number formulation. The latter can be employed within a wide range of turbulence models, without limiting its variability. / Doctorat en Sciences de l'ingénieur et technologie / info:eu-repo/semantics/nonPublished

World resources are becoming more and more scarce due to the increasing demand. Hence, the industry is moving towards sustainable development in order to suffice the needs of the future generations. Electricity is one such resources that account for 90% of the daily utility. In Sweden alone 378 TWh of electricity is consumed over a year. The major source of production of electricity is the fossil fuels, but due to development in the renewable resource's the electricity is also produced using solar, wind and geothermal energy. However, no production process is 100% efficient and hence, there is loss of energy in the form of waste. Organic Rankine Cycle Turbine (ORC) is a technology which is under the focus of the researcher and the industry to convert this wasteful energy into useful energy. Designing of these machines is a challenging task which requires careful consideration of every design parameter, i.e. with the change in every parameter the losses in the turbine either increase or decrease. In this study, effect of the parameters such as inlet mach number, stagger angle, inlet angle and pitch to chord is studied to see the effect on the profile loss. Since ANSYS Fluent works with 2D unlike ANSYS CFX which work with pseudo 2D geometry, ANSYS Fluent was used for investigating profile loss. Furthermore, a methodology is defined to investigate the tip leakage loss based on the geometry provided by the Againity AB for future studies. Tip leakage loss simulations were carried out in ANSYS CFX turbo mode due to its user friendly interface for simulating turbo machinery flows. The results of the profile loss investigation suggested a range for parameters where the profile loss is observed to be comparatively lower than elsewhere. The methodology proposed for tip leakage loss investigation paved a pathway for the further improvement with respect to the future studies.

The master's thesis is devoted to the design development, the calculation of the thermal and gas-dynamic modes of operation of a furnace furnace of the baraban type, designed to heat metal products before quenching. In the course of work, heat engineering calculations were carried out for a new drum-type furnace design, the heat balance of the furnace was obtained, and computer simulation of gas dynamics in the working space of the chamber furnace was carried out in the Ansys Fluent software module. The results of the work can be used in the performance of research and development work at metallurgical enterprises, as well as in the educational process for training bachelors and undergraduates in the direction of “Metallurgy” (bachelor’s and master’s level). / Магистерская диссертация посвящена разработке конструкции, расчету теплового и газодинамического режимов работы камерной печи барабанного типа, предназначенной для нагрева металлических изделий перед закалкой. В ходе работы проведены теплотехнические расчеты для новой конструкции печи барабанного типа, получен тепловой баланс печи, в программном модуле Ansys Fluent проведено компьютерное моделирование газодинамики в рабочем пространстве камерной печи. Результаты работы могут быть использованы при выполнении научно-исследовательских работ на металлургических предприятиях, а также в учебном процессе для обучения бакалавров и магистрантов по направлению «Металлургия» (уровень бакалавриата и магистратуры).

With the advent and increasing influence of lithium-ion batteries, it is imperative to devise the means for realizing a safe operation of the same. Battery modelling of lithium-ion cells is a means to comprehend the cell behaviour. A battery model includes both physical and mathematical modelling with each having their individual pros and cons. Depending on the scale of the battery model resolution the complexity and computational time increases. This thesis work deals with the development of a thermal model for 18650 cylindrical lithium-ion cells. This model encapsulates the thermal behaviour of the STB4 product at Atlas Copco and the battery model development has been done in conjunction with a 3D Computational Fluid Dynamic (CFD) analysis in Ansys Fluent to comprehend the heat distribution over the product surface and identify thermal bottlenecks. The model selection has been done based on the required level of functionality and its effect on the computational time. The proposed NTGK electrochemistry model in this thesis based on the Circuit Network solution method, provides an optimal balance between computational efficiency and model accuracy. The consolidated battery model and analysis results provide crucial insight towards the thermal patterns of the lithium cells and help indicate deviations in case of potential unsafe operation. The simulation model has been validated against the physical experimental tests performed on the battery pack and the STB4 provided by Atlas Copco. Finally, an approach towards a future software implementation of the developed model is outlined in this thesis. / Med tillkomsten och ökande inflytande av litiumjonbatterier är det absolut nödvändigt att utarbeta medel för att förverkliga en säker drift av desamma. Batterimodellering av litiumjonceller är ett sätt att förstå cellens beteende. En batterimodell inkluderar både fysisk och matematisk modellering där var och en har sina individuella för- och nackdelar. Beroende på storleken på batterimodellens upplösning ökar komplexiteten och beräkningstiden. Detta examensarbete behandlar utvecklingen av en termisk modell för 18650 cylindriska litiumjonceller. Denna modell kapslar in det termiska beteendet hos STB4-produkten hos Atlas Copco och utvecklingen av batterimodeller har gjorts i samband med en 3D Computational Fluid Dynamic (CFD)-analys i Ansys Fluent för att förstå värmefördelningen över produktytan och identifiera termiska flaskhalsar. Modellvalet har gjorts utifrån den funktionalitet som krävs och dess effekt på beräkningstiden. Den föreslagna NTGK elektrokemimodellen i denna avhandling baserad på lösningsmetoden Circuit Network, ger en optimal balans mellan beräkningseffektivitet och modellnoggrannhet. Den konsoliderade batterimodellen och analysresultaten ger avgörande insikt om litiumcellernas termiska mönster och hjälper till att indikera avvikelser i händelse av potentiell osäker drift. Simuleringsmodellen har validerats mot de fysiska experimentella testerna som utförts på batteripaketet och STB4 från Atlas Copco. Slutligen beskrivs ett tillvägagångssätt för en framtida mjukvaruimplementering av den utvecklade modellen i denna avhandling.

This paper covers information research of basic design rules of industrial wet sumps. It describes mathematical models of vortices and method for their identification and visualization. Then the author focuses on CFD modeling of surface vortices with single phase and multiphase approach with Volume of Fluid method. Basic principles of multiphase CFD modelling in OpenFOAM and ANSYS Fluent are given. Description and benchmarking of suitable turbulence models is also present. The single phase and multiphase approach were successfully validated for a simple test case of bathtub surface vortex. Satisfactory agreement with experimental data was achieved. The accuracy and behavior of both solvers were compared between each other. This gives us useful tool for evaluation of inflow condition and danger of surface vortex occurrence in wet sumps. The acquired knowledges were used to design an experimental test case with geometry similar to industrial wet sump. A map of surface vortex occurrence has been created for different operating points. One of the operating point has been used for numerical simulation (both single phase and multiphase). Partial agreement with experimental observation has been achieved.

This thesis is focused on electron microscopy which issue is discussed at the beginning of work. The main attention is dedicated to the Environmental electron microscope, especially the differentially pumped chamber, which the thesis deals with. There is a production of an experimental chamber for analysis of shock waves on going therefore main goal of this thesis was to analyze the flow pattern in this chamber. Using the Ansys Fluent program, simulations of the characteristic flow that arises from the pumping of the vacuum chambers namely the ultrasonic flow at low pressures on which the most suitable turbulent module was applied as well as the degree of discretization was performed. The final analysis of this flow pattern is primarily focused on the localization of the shock wave which experimental evidence is to be lodged by shadow optical method as a part of the new concept of the chamber. The basis for the simulation of the chamber was taken over by Dr. Danilatos, with which the results were compared.