Tahle práce se zaměřila na aerodynamickou analýzu principů zvyšování pumpážních záloh. V první kapitole jsou popsány kompresory leteckých motorů a zavedeny potřebné znalosti kompresorových charakteristik a proti-pumpážních zařízení. V druhé kapitole se nachází detailní popis CFD modelu, jeho nastavení, citlivostní analýzy sítě a korelace výsledků s experimentálním měřením. V třetí kapitole jsou popsány data neupraveného kompresoru a jsou zde popsány problematická místa první stupně kompresoru z pohledu proti-pumpážních zařízení. Ve čtvrté kaptiole jsou popsány CFD výsledky z analýz jednotlivých proti-pumpážních zařízení a také popis jejich optimalizace. Práce je zakončena srovnáním jednotlivých zařízení pomocí dvou objektivních kritérií.

The aim of this master´s thesis was to model the fan for the induction motor, and then to solve this model using Ansys CFX in the terms of flow, when considering the different speeds of rotation of the rotor. The introduction of this work is dedicated to basic terms and definitions from spheres of fluid flow, cooling of the electrical machines, especially to the cooling of the asynchronous machine. There is also attention paid to losses in this machine. Finally, there is modeled radial fan and an air gap of specified induction machine. By using Ansys CFX the flow, which passes from the fan into the air gap, is analyzed.

The thesis is focused on possibilities of asynchronous motors cooling with use of simulation at ANSYS Workbench program. It is divided into two parts. The first part deals with analyses of cooling medium circulation through ventilator and cooling medium circulation on the motor surface. As a result of the analyses is air speed distribution and air pressure representation. The second part of the thesis includes simulation of motor temperature rise both with cooling and without cooling at Ansys Workbench application together with temperature measurement of real asynchronous motor in the laboratory. For cooling purposes air circulation was used. The goal of my research is comparison of the computing results with the measured results.

This master´s thesis deals with influence of forced air flow from the ventilators on the power transformer cooling. For this analysis was used simulation software ANSYS CFX, that uses the finite volume method for calculations of dynamic properties of liquids. In the introduction of the thesis is presented the basic terminology of fluid flow, temperature fields and theory of transformers. The simulation is divided to the analysis of flow through the left and right radiator models.

This work is focused on the dynamic effects with regard to impact of wind on a slender bridge structure, namely a variant of an overhead footbridge for pedestrians and cyclists, over a river. Attention is focused on finding the so-called default steady state, as well as modal analysis, where owen frequencies are calculated, which is the basis for further dynamic assessment. The main part is focused on modeling in a fluid field of ANSYS CFX, where the effects of wind on the structure are defined and calculated. The goal of the work is to make a dynamic response to vortex excitation and, on the basis of analysis, to assess the fatigue design.

Three-dimensional turbulent flow in a cylindrical hydrocyclone is considered and studied by means of computational fluid dynamics using software packages CFX and Fluent. The aim has been to identify the methods that can be used for accurate simulation of the flow in three-dimensional configurations in hydrocyclones at high swirl numbers. As a starting point, swirling pipe flows created by tangential inlets, where detailed experimental data were available in literature, were considered. It was found that the velocity profiles for the flow with a swirl number of 2.67 could be predicted accurately using a Reynolds stress model and an accurate numerical discretization on a fine-enough mesh. At a higher swirl number, 7.84, under-prediction in the tangential velocity profiles was observed; however the prediction of the axial velocity profiles was satisfactory. The validated methods were then used to simulate the flow in a cylindrical hydrocyclone at a swirl number as large as 21. The calculated tangential velocity profiles were compared against experimental data measured with a pitometer. Acceptable agreements were recorded except near the geometric axis of the cyclone. Due to the lack of the aircore in the numerical model, disagreements near the axis of the cyclone could be expected to some extent. Numerical experiments performed in the present work indicated that the RNG k-ε model is not likely to be capable to predict highly swirling flows accurately and a Reynolds stress model is required. For three-dimensional models, where the computing capacity and the available memory set strong restrictions on the computational mesh, optimizing the maximum mesh resolution available play an important role on the accuracy and stability of the solution procedure. The most stable results in the present study were found using the Reynolds stress model proposed by Launder et al. on an as regular and structured mesh as possible using a higher order discretization scheme in Fluent. Therefore, the meshing capabilities of the pre-processor, the available turbulence models and the accuracy of the numerical methods must be considered in parallel. Acceptable results were also generated using the Baseline Reynolds stress model implemented in CFX, however, only with a transient procedure which was likely to be more time-consuming. Present simulations present a complex flow structure in the cylindrical cyclone with a double axial flow reversal. The effect of such a flow pattern on the fractionation of the fibres with small differences in density needs to be investigated in future studies. / QC 20101207

With growing awareness and necessity for the world to move towards more sustainable (energy saving) forms of power generation, focus on the commercial use of Organic Rankine Cycle (ORC) turbine systems has subsequently increased in turn. ORC systems with their modular design can thus help in recovering heat, obtained as a byproduct from a variety of industrial processes, and thereby increase their overall system efficiency. As with conventional turbine systems, methods to improve their performance is an avenue that is still being actively researched on today. The various sources of losses in a turbine have thus been looked into, while prioritizing the literature study to factors that result in losses associated with the leakage flow over the blade tip. The purpose of this study is to develop a working methodology to investigate factors that affect the tip leakage loss in a small scale ORC turbine. The model and associated data used for comparison is based on an existing system, whose design has been provided by Againity AB, with the subsequent simulations carried out using Ansys CFX.

Conventional primary Li/CFx batteries employ graphite and polyvinylidene fluoride additives in the cathodes. These additives usher in some un-desired side-effects, such as lower battery capacities (mAh/g) and smaller current densities (mA/g). An innovative pretreatment was developed in this research in which CFx was subject to a “solvated electron” reduction to obtain a thin layer graphitic carbon coating on the CFx particle surfaces. Resistivity tests revealed that these partially reduced CFx particles have a higher conductivity at comparable graphitic carbon contents. Electrochemical discharge reactions demonstrated that batteries made from the reduced CFx were superior to the conventional batteries with higher current densities and higher capacities achieved. Impedance spectroscopy (EIS) studies found out that the reduced CFx particles have smaller cell reaction resistances, smaller double layer/intercalation capacitances and smaller mass transport resistances. It appears that use of reduced CFx has the potential to replace the conventional CFx plus additives as a cathode material in Li/CFx batteries.

This master thesis project consisted of three parts that all were performed through CFD simulations with the purpose to develop Scania's methods in the subject of CFD. All parts included simulations on Scania's SC92T70 centrifugal compressor. Part one consisted of performing a mesh study for the purpose of reliability, to investigate the convergence of different parameters by refining the boundary layer. The method used is an inflation option called First layer thickness. Five different meshes were generated where the Richardson extrapolation method was used to examine the parameters between the mesh renements. From the result from the examined parameters, an approximate relative error could be calculated to be less than 0.52 %, and a numerical uncertainty of less than 0.35 %, between Mesh3 and Mesh4. In addition to that, Mesh3 had a simulation time of one hour less than for Mesh4. These results motivated the use of mesh3 to be refined enough for further work in this thesis project. This mesh ended at 37, 915, 257 number of elements. The second part consisted of performing steady state CFD simulations, to examine different parameters in order to find indications of the phenomena surge. Here, experimental data was used as reliance to perform CFD simulations on the compressor. Design points from experimental data was used, that ranged from low mass flow rates where surge arises, to high mass flow rates where another phenomena called choke occur. Except for the design points taken from experimental data, a few extra design points where included at low mass flow rates (in the region of surge). The goal was that the analysis of the different parameters would generate fluctuations on the result for the design points in surge region. Four different rotational speeds on the compressor were examined, 56k, 69k, 87k and 110k revolutions per minute. A total of 140 different parameters were examined, where 10 of these indicated on surge. All of these parameters that indicated on surge where found in regions of vicinity to the compressor wheel, which are the regions subjected to the phenomena.The parameters indicating on surge where mass flow, pressure coefficient, static pressure and temperature. Indications where found at the wheel inlet, ported shroud, and wheel outlet interfaces. The indications were only found for the two lower rotational speeds of the compressor wheel. To capture the behaviour on higher rotational speeds, more design points in the region of surge are needed, or transient simulations. Part three of the thesis project consisted of investigating the methodology of performing a Conjugate Heat Transfer model (CHT) with the CFD code CFX. This part has not been performed by Scania before, so a big part of the problem was to investigate if it actually was achievable. The goal was to use this model to calculate the heat transfer between fluid and solid parts, as well as between the solid parts and the ambient. One question Scania wanted to answer was if the CHT model could generate aerodynamic performance that corresponds to Scania's traditional adiabatic model, as well as to experimental data of the compressor. In this part, both solid and fluid domains were included in the geometryto calculate heat transport, in contrast to the traditional adiabatic model that only uses the fluid domains. Because of that, a big part of the work consisted of defining all interfaces connecting together surfaces between all domains. This is needed to model heat transport between the domains. In the set up part in CFX, the CHT model differed a lot from the traditional adiabatic model in that way that the outer walls was not set up as adiabatic anymore. In the CHT model, instead heat transfer is allowed between the outer walls of the fluids and the solids. From the result simulations, one could see that the CHT model was able to compute the heat transfer between fluids and solids. It also managed to export thermal data such as heat flux and wall heat transfer coefficient to be used for mechanical analysis, which is an important part in Scania's work. From the analysis of aerodynamic performance, a conclusion was drawn that the CHT model was able to compute efficiency and pressure ratio that followed the behaviour ofthe traditional adiabatic model as well as experimental data. However, for lowermass flows, the CHT model started to underpredict which could be explained by the geometrical differences between the CHT and adiabatic model. By analysis of temperature, one could see quantitative differences compared to the traditional adiabatic model. For other parameters (static and total pressure), there were no experimental data to be used for comparison. Because of that, an important part in future work of this CHT method development is to perform more experimental test for CFD data to be compared against. Another important part to compare the models is to have an identical geometry. Without an identical geometry, deviations in result will occur that depends on geometry.

Steam turbines are widely used in various industrial applications, primarily for power extraction. However, deviation for operating design conditions is a frequent occurrence for such machines, and therefore, understanding their performance at off design conditions is critical to ensure that the needs of the power demanding systems are met as well as ensuring safe operation of the steam turbines. In this thesis, the aerodynamic performance of three different turbine airfoil sections ( baseline, mid radius and tip profile) as a function of angle of incidence and exit Mach numbers, is numerically computed at 0.3 axial chords downstream of the trailing edge. It was found that the average loss coefficient was low, owing to the fact that the flow over the airfoils was well behaved. The loss coefficient also showed a slight decrease with exit Mach number for all three profiles. The mid radius and tip profiles showed near identical performance due to similarity in their geometries. It was also found out that the baseline profile showed a trend of substantial increase in losses at positive incidences, due to the development of an adverse pressure zone on the blade suction side surface. The mid radius profile showed high insensitivity to angle of incidence as well as low exit flow angle deviation in comparison to the baseline blade. / Master of Science