Dissertations / Theses on the topic 'Computational gas dynamics'

The ingestion of hot mainstream gas into the wheel-space between the rotor and staler discs is one of the most important internal cooling problems for gas turbine designers. To solve this problem, engineers design a rim seal at the periphery of wheel-space and direct a sealing flow from the internal cooling system to prevent ingress. The main aim of this thesis is to build a simple computational model to predict the scaling effectiveness of externally-induced ingress for engine designers. The axisymmetric model represents a gas turbine wheel-space and provides useful information related to the fluid dynamics and heat transfer in the wheel-space. At the same time, this model saves much computation time and cost for engine designers who currently use complex and time-consuming 3D models. The- computational model in this -thesis is called the prescribed ingestion model. Steady simulations are carried out using the commercial CFD code, ANSYS CFX with meshes built using ICEM CFD. Boundary conditions are applied at the ingress inlet of the model using experimental measurements and a mass-based averaging procedure. Computational parameters such as rotational Reynolds number, non-dimensional sealing flow rate and thermal conditions on the rotor are selected to investigate the fluid dynamics and heat transfer at typical experimental rig operating conditions. Different rim seal geometries arc investigated and results are compared with experimental data. In addition to the prescribed ingestion model, two typical axisymmetric rotor-stator system models without ingress arc established. The aim of these rotor-stator models is to investigate the fluid dynamics and heat transfer of the wheel-space in the situation without ingress. The effects of geometry and turbulence model also arc studied in these simulations. Most results from these simulations are in good agreement with experimental data from the literature, which enhances confidence in the prescribed Ingestion model.

"Liquid piston gas compression utilizes a liquid to directly compress gas. The benefit of this approach is that liquid can conform to irregular compression chamber volume. The compression chamber is divided into many small little bores in order to increases the surface area to volume ratio. The heat transfer rate increases with increasing surface area to volume ratio. However, as the bore diameter becomes smaller, the viscous force increases. In order to maximize the heat transfer rate and to minimize the viscous force, computational fluid dynamics is used. ANSYS Fluent is used to simulate the liquid piston gas compression cycle. Having created the model in Fluent, different factors, including diameter, length, liquid temperature, and the acceleration are varied in order to understand how each factor affects the heat transfer and viscous energy loss. The results show that both viscous force and heat transfer rate increase as the diameter decreases. The viscous force increases and the heat transfer decreases as the length increases. Both the viscous force and heat transfer increase as the acceleration increases. The viscous force decreases as the liquid temperature increases. Results show that the highest compression efficiency of 86.4% is found with a 3mm bore radius and a short cylinder. The piston acceleration is advised to be below 0.5g in order to avoid surface instability problem."

Thesis (M.S.)--West Virginia University, 2006.<br>Title from document title page. Document formatted into pages; contains ix, 83 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 65-67).

Thesis (Ph.D.)--Chemical Engineering, Georgia Institute of Technology, 2008.<br>Committee Chair: Charles A. Eckert; Committee Co-Chair: Charles L. Liotta; Committee Member: J. Carson Meredith; Committee Member: Rigoberto Hernandez; Committee Member: William J. Koros

Within the oil industry there is a need to measure and predict the form of the multiphase liquid and gas flows that are present within oil production and processing pipelines. Knowledge of the flow regimes present allows the engineer to optimise the configuration of the pipeline and downstream processes to achieve the most, economic and reliable design. The applications of these technologies are collectively known as flow assurance. Within oil production systems, one component which has received little attention is the characterisation of the multiphase flow around bends under various process conditions. To predict the flow regimes in greater details requires the development of instrumentation that can measure and characterise the flow within the pipes. To circumvent this challenge, two experimental investigations were carried out in two rigs available in the Chemical and Environmental Engineering Laboratories at the University of Nottingham. These are: (1) a 67 mm internal diameter pipe joined to a 90o bend, in which air/silicone oil flows were investigated using advanced instrumentation: Electrical Capacitance Tomography (ECT), Wire Mesh Sensor Tomography (WMS), and high-speed video. The first two provide time and cross-sectionally resolved data on void fraction. The ECT probes were mounted 10 diameters upstream of the bend whilst the WMS was positioned either immediately upstream or immediately downstream of the bend. The downstream pipe was maintained horizontal whilst the upstream pipe was mounted either vertically or horizontally. The bend (R/D = 2.3) was made of transparent acrylic resin. The superficial velocities of the air ranged from 0.05 to 4.73 ms-1 and for the silicone oil from 0.05 to 0.38 ms-1. (2) a 127 mm internal diameter riser joined to a vertical 180o bend, in which measurements of film fraction and liquid film thickness distribution for an air-water system were obtained using the electrical conductance technique. The former was measured using the ring conductance probes placed 17 and 21 diameters, respectively upstream and downstream of the bend, 45o, 90o and 135o within the bend. The latter were obtained using pin and parallel wire probes. The pin probes were used for thin films measurement whilst the parallel wire probes for thick films. The bend, made of transparent acrylic resin, has a curvature ratio (R/D = 3). The superficial velocities of the air ranged from 3.5 to 16.1 ms-1 and for the water from 0.02 to 0.2 ms-1. The experimental results for the 90o bend study reveal that bubble/spherical cap bubble, slug, unstable slug and churn flows were observed before the bend for the vertical pipe and plug, slug, stratified wavy and annular flows when the pipe was horizontal. Bubble, stratified wavy, slug, semi-annular and annular flows are seen after the bend for the vertical 90o bend, the flow patterns remained the same as before the horizontal 90o bend. These results were confirmed by the high-speed videos taken around the bend. For the vertical 180o return bend, the average film fraction was identified to be higher in straight pipes than in bends. For low liquid and higher gas flow rates, due to the action of gravity drainage, film breakdown occurs at the 45o bend. A previously proposed criterion, to determine stratification after the 90o bend, based on a modified Froude number have been shown to be valid for a liquid different from that tested in the original paper. Similarly, for the 180o return bend, the condition for which the liquid goes either to the inside or outside of the bend are identified based on published material. Variations between average liquid film thickness and bend angles are reported for the vertical 180o bend. Contrary to the conclusions reached by Hills (1973) and Anderson and Hills (1974), the liquid film thickness becomes annular flow in the 180o bend at low liquid flow rates and stratified flow at higher liquid superficial velocities. In addition, a CFD code has been used to successfully model the hydrodynamics of the slug flow pattern in a riser and vertical 90o bend, using the Volume of Fluid model based on the Eulerian approach, implemented in the commercial CFD package Star-CCM+. The modelling results are validated with the experiments and also provide more detailed information on the flow such as the velocity field.

A modern gas turbine must be designed quicker, be more reliable, produce less emissions than its predecessors and yet the engine manufacturer must still make a profit. In order to sell their engines to the airlines, the manufacturer must show that their engines meet strict safety and reliability requirements. The creation of finite element models used for predicting temperatures and displacements of the engine component's is part of this design cycle. This thesis addresses the use of computational fluid dynamics (CFD) as a tool that can help in the prediction of iiietal temperatures for use with "industrial" problems and the associated requirements of accuracy and time-scales. The definition of 'industrial" accuracy and time-scales in this thesis is the accuracy required to enhance the modelling capability of a thermal engineer in design time-scales. A method is developed for using a commercial CFD code. FLUENT, for predicting flow and heat transfer. The code has been validated against several benchmark test cases and has shown good predictive capability and mesh independence for flow and heat transfer in the cavity between a rotating and stationary disc with and without through-flow. For cavities between co-rotating discs with radial througliflow, the predictions are acceptable, but some sensitivity of the heat transfer results to mesh spacing has been identified. The code has also been validated against some "industrial" test cases where experimental data has been available. The effects of buoyancy in the centrifugal force field are discussed and are related to a buoyancy number. The next part of the thesis develops a method of solving the heat transfer problem by coupling a finite element code, SC03, with FLUENT. The ideas are developed on two simple test cases and the problems of what information is to be passed across the coupling boundary and convergence issues are discussed. The results show that passing heat transfer coefficients and local air temperatures achieves the best convergence. The coupled method is their tested against two 'industrial problems. It is concluded that the method has considerable potential for use in design although some difficulties in applying the method are identified. Although not demonstrated, the method developed is not specific to SC03 or FLUENT and ally heat traiisfer/ CFD codes could be used.

Thesis (M.S.)--University of California, San Diego, 2007.<br>Title from first page of PDF file (viewed November 21, 2007). Available via ProQuest Digital Dissertations. Includes bibliographical references (p. 56-57).

Thermoacoustic instabilities arise and sustain due to the coupling of unsteady heat release from the flame and the acoustic field. One potential driving mechanism for these instabilities arise when velocity fluctuations (u') at the fuel injection location causes perturbations in the local equivalence ratio and is convected to the flame location generating an unsteady heat release (q') at a particular convection time delay, τ. Physically, τ is the time for the fuel to convect from injection to the flame. The n-τ Flame Transfer Function (FTF) is commonly used to model this relationship assuming an infinitesimally thin flame with a fixed τ. In practical systems, complex swirling flows, multiple fuel injections points, and recirculation zones create a distribution of τ, which can vary widely making a statistical description more representative. Furthermore, increased flame lengths and higher frequency instabilities with short acoustic wavelengths challenge the 'thin-flame' approximation. The present study outlines a methodology of using distributed convective fuel time delays and heat release rates in a one-dimensional (1-D) linear stability model based on the transfer matrix approach. CFD analyses, with the Flamelet Generated Manifold (FGM) combustion model are performed and probability density functions (PDFs) of the convective time delay and local heat release rates are extracted. These are then used as inputs to the 1-D Thermoacoustic model. Results are compared with the experimental results, and the proposed methodology improves the accuracy of stability predictions of 1-D Thermoacoustic modeling.<br>Master of Science

A deep understanding of molecular reactions is a challenging task since the range of time and energy covered implies a wide and dense grid for the numerical representation of the reactive Hamiltonian. For a computational chemist, the accurate prediction of its value starting from the definition of reactants and products is fascinating and demanding, but can be extremely useful for further investigation and optimization problems. Several methods, all derived by the Transition State Theory, have been developed to avoid the computational cost of the Hamiltonian representation on a large, multidimensional grid; we investigate these strategies both in the time and energy domain to explore the advan- tages and drawbacks of these reciprocal spaces. Since we want to increase the range of applicability of the calcula- tion of thermal rate constants to medium size molecules, which can have floppy geometries with low frequency modes, we introduce a dedicated treatment of such modes based on the Intrinsic Reaction Path of Fukui. In Part i, we introduce the theoretical instrument used to perform our calculation, both in energy and time domain; Part ii is devoted to the presentation of the applications, mainly focused on current issues in astrochemical studies. Appendices treat specific topics, like Möller operators, essential for the comprehension of the theory but too long to be inserted in Part i.

Although the native environment of the vast majority of proteins is a complex aqueous solution, like the interior of a cell, many analysis methods for assessing chemical and physical properties of biomolecules require the sample to be aerosolized; that is, transferred to the gas-phase. An important example is electrospray-ionization mass spectrometry, which can provide a wide range of information about e.g. biomolecules. That includes structural features, charged sites, and gas-phase equilibrium constants of reactions. To date much of the microscopic detail about the aerosolization process remains beyond the limits of experimental observation. How is the gas-phase structure of a protein related to the solution-phase structure? How transferable are observations done in the gas phase to solution? On the basis of classical molecular-dynamics simulations this thesis reveals important features of gas-phase biomolecular structure near the end of the the aerosolization process, the relation between gas-phase structure and native structure, microscopic detail about the de-wetting of gas-phase biomolecules, and the impact of temperature and residual solvent on structure preservation. Residual solvent on proteins is shown to have a stabilizing effect on proteins, in part because it allows the scarcely hydrated protein to cool through solvent evaporation, but also because part of the solvent provides structural support by hydrogen bonding to the protein. The gas-phase structure of micellar aggregates is seen to depend on composition, where some types of lipids cause rapid micelle inversion, whereas others maintain much of their collective structure when transferred to the gas phase. The thesis also addresses proton-transfer reactions, which have an impact on the biophysical aspects of proteins, both in the gas phase and in solution. The thesis presents a computationally efficient method for including proton-transfer reactions in classical molecular-dynamics simulations, which expands the range of scientific problems that can be addressed with molecular dynamics.

In the past few decades, the operating temperatures of gas turbine engines have increased significantly with a view towards increasing the overall thermal efficiency and specific power output. As a result of increased turbine inlet temperatures, the hot gas path components downstream of the combustor section are subjected to high heat loads. Though materials with improved temperature capabilities are used in the construction of the hot gas path components, in order to ensure safe and durable operation, the hot gas path components are additionally supplemented with thermal barrier coatings (TBCs) and sophisticated cooling techniques. The present study focusses on two aspects of gas turbine cooling, namely augmented internal cooling and external film cooling. One of the commonly used methods for cooling the vanes involves passing coolant air bled from the compressor through serpentine passages inside the airfoils. The walls of the internal cooling passages are usually roughened with turbulence promoters like ribs to enhance heat transfer. Though the ribs help in augmenting the heat transfer, they have an associated pressure penalty as well. Therefore, it is important to study the thermal-hydraulic performance of ribbed internal cooling passages. The first section of the thesis deals with the numerical investigation of flow and heat transfer characteristics in a ribbed two-pass channel. Four different rib shapes- 45° angled, V-shaped, W-shaped and M-shaped, were studied. This study further aims at exploring the performance of different rib-shapes at a large rib pitch-to-height ratio (p/e=16) which has potential applications in land-based gas turbines operating at high Reynolds numbers. Detailed flow and heat transfer analysis have been presented to illustrate how the innate flow physics associated with the bend region and the different rib shapes contribute to heat transfer enhancement in the two-pass channel. The bend-induced secondary flows were observed to significantly affect the flow and heat transfer distribution in the 2nd pass. The thermal-hydraulic performance of V-shaped and 45° angled ribs were better than W-shaped and M-shaped ribs. The second section of the study deals with the analysis of film cooling performance of different hole configurations on the endwall upstream of a first stage nozzle guide vane. The flow along the endwall of the airfoils is highly complex, dominated by 3-dimensional secondary flows. The presence of complex secondary flows makes the cooling of the airfoil endwalls challenging. These secondary flows strongly influence endwall film cooling and the associated heat transfer. In this study, three different cooling configurations- slot, cylindrical holes and tripod holes were studied. Steady-state experiments were conducted in a low speed, linear cascade wind tunnel. The adiabatic film cooling effectiveness on the endwall was computed based on the spatially resolved temperature data obtained from the infrared camera. The effect of mass flow ratio on the film cooling performance of the different configurations was also explored. For all the configurations, the coolant jets were unable to overcome the strong secondary flows inside the passage at low mass flow ratios. However, the coolant jets were observed to provide much better film coverage at higher mass flow ratios. In case of cylindrical ejection, the effectiveness values were observed to be very low which could be because of jet lift-off. The effectiveness of tripod ejection was comparable to slot ejection at mass flow ratios between 0.5-1.5, while at higher mass flow ratios, slot ejection was observed to outperform tripod ejection.<br>Master of Science

Liquefied Natural Gas (LNG) is currently playing an important role in the world energy markets. This is evidenced by growing demand and increased construction of LNG facilities across Europe and the United States. In the event of spill from any of the facilities handling LNG such as during liquefaction, transportation or regasification, flammable vapour is formed which disperses through the atmosphere constituting fire and explosion hazards. To ensure public safety in the midst of growing LNG demand and facilities construction, industries are usually mandated to demonstrate that public safety will not be undermined by potential spill from their facilities. One method that is currently being used to demonstrate compliance is through LNG vapour dispersion modelling using Computational Fluid Dynamics (CFD). CFD modelling of dispersion phenomena is a challenging task that requires rigorous methodology to account for the underpinning physical processes. The modelling process comprises of two steps: source term quantification and vapour dispersion modelling. Source term quantification involves the physical description of spill rate, pool spreading and evaporation. Vapour dispersion utilizes the result of source term quantification in order to predict the turbulent entrainment and dilution process with the ambient wind. Existing models employ simplifying assumptions that circumvents explicit source term modelling. The spilled liquid is assumed to fill the entire substrate immediately at which time the spill rate becomes equal to evaporation rate. Following this assumption, a fixed inlet patch area and evaporation rate is applied at the gas inlet boundary. This approach fails to incorporate the transient pool development and subsequent evaporation into the dispersion modelling process. The primary aim of this dissertation is to develop an efficient integrated pool spreading, evaporation and dispersion (I-PSED) model code for LNG vapour dispersion simulation. This represents a significant shift from the traditional method since the new methodology combines the spilling process, spreading on substrate and transient evaporation into a unified model. For the spilling process, the well- known orifice model has been adopted to predict the spill rate taking into account the decreasing head. A mass balance approach is adopted in conjunction with a well¬established similarity model for spreading calculation. Heat transfer to the spreading pool is incorporated based on film boiling correlation. The spreading model was then coupled to an atmospheric dispersion model within OpenFOAM framework through the implementation of a new boundary condition in which the gas inlet patch area changes based on the instantaneous pool radius. The developed integrated code (I-PSED) is validated against data from the Coyote Series LNG Spill experiments as well as against Shell's Maplin Sand LNG spill experiments. Predictions of concentration obtained using the proposed model and those obtained using conventional approach are compared against experimental data at specific sensor locations. Also, arc-wise comparisons are carried out. Predicted results show good agreement with experimental data and clearly put the newly developed model ahead of the conventional approach for CFD simulation of LNG vapour dispersion. With the newly developed approach, the cloud arrival time and average concentrations at most sensor locations were better predicted. The effect of the turbulent production due to density stratification (buoyancy) created by the release of cryogen is investigated. Experience gathered shows that incorporation of a production term due to buoyancy in the turbulence model improves predictions under unstable atmospheric condition, otherwise the concentration field would be grossly over-predicted.

Properties of functional polymeric materials can be tuned by either varying the composition of a multi-component system, or by chemical modification of the constituents. Thus it is extremely crucial to develop a molecular level understanding of these interactions and the role of composition that manifests into desired functional properties. The present thesis involves computer simulation studies of various polymeric systems investigating the effect of composition and interactions on the polymer properties at a molecular level. The thesis has been classified into three major parts based on the selected polymer or property of interest as follows. In Part A and B, interactions in polymeric systems are modified by changing the compositions, by incorporating additives in part A and altering chemical structure of polymer in part B. Part C investigates the gas adsorption characteristics of a polymeric system and the role of structural and dynamical heterogeneity therein. In Chapter 1, the thesis introduces the systems under consideration and presents a brief review of the literature. Subsequently, a description of applied computational methods and concepts is given in Chapter 2. These chapters are common to all parts A, B and C. Separate introductions and computational details relevant to each part are further discussed in individual parts. Part A It includes chapter 3, 4 and 5. The systems under study in part A are rubber and rubberplasticizer mixtures, focusing majorly on deciphering the molecular mechanisms related to glass transition and its impact on structural and dynamic properties of rubbers. Chapter 3: A brief overview of properties of rubber, rubber composites and rubber blends is presented. Emphasizing the fact that a systematically validated force-field and proper equilibration are the major pre-requisites for any polymer simulation. In the first working chapter of this thesis, we have validated quantum-chemically derived force-fields of rubber by calculating glass transition temperature (Tg), density and local chain characteristics like end-to-end distance and radius of gyration (Rg). All calculated properties have been compared to corresponding experimental results and force fields are also tuned in cases where calculated properties do not match with experiments. A potential energy based equilibration protocol has been proposed and tested for rubbers under study: cis and trans- Polybutadiene and Polyisoprene. Chapter 4: Additives are incorporated in rubber-matrix to enhance the mechanical and physico-chemical properties of rubbers for their optimum use in tire and other rubber industries. Plasticizers are the additives which increases the flexibility and processibility of rubbers. This chapter is focused on deducing the molecular mechanisms of plasticizer action in rubbers. Effect of plasticizers on structural and dynamic properties of rubber has been analyzed. Various polymer properties like free volume, end-to-end distance, Rg, autocorrelation functions, mean square diffusion, structural and dynamic heterogeneity have been explored. Chapter 5: The most common method employed for calculating Tg of polymers from MD simulations involves deducing temperature dependence of properties like density and specific volume. The slope of density-temperature plot gives Tg. However this protocol is computationally expensive involving polymer equilibration at temperatures below Tg. In this chapter, we have proposed a method of calculating Tg from segmental (α) relaxation times at temperatures higher than Tg. Incoherent intermediate scattering function Fs(q,t) are used to calculate relaxation times and then Tg is calculated using Vogel-Fulcher-Tamman equations. Part B It includes chapter 6. The system under study is ionomer melt of star telechelic D, L-polylactide and the property under investigation is viscosity. Chapter 6: Star D,L-Poly-lactic acid (PDLLA) shows the typical exponential decrease in viscosity with temperature. However ionomer formed by replacing acid groups of chain ends with sodium carboxylate ions, shows a significant increase in elasticity and non-monotonic temperature dependence of viscosity at temperatures above Tg, which is unusual. The molecular mechanism responsible for the non-monotonic temperature dependence of viscosity has been investigated in this chapter. Part C It includes chapter 7. The system under study is Polyethyleneimine (PEI) and its carbon dioxide capture properties have been investigated. Chapter 7: A brief introduction of existing carbon dioxide capture technologies focusing on the merits and demerits of each method is provided. Characteristics of CO2 capture through polymeric membranes, especially nitrogen containing polymers is discussed. The mechanism of CO2 adsorption in PEI is investigated using Grand Canonical Monte Carlo (GCMC) and Molecular dynamics (MD) simulation studies. A detailed analysis of intermolecular interactions between PEI and CO2 at the interface, bulk and local structural regions of PEI melt has been performed to assess the adsorption effectiveness. Effect of structural and dynamic heterogeneities on adsorption process has been analyzed. Chapter 8: A brief summary of the research work and derived conclusions is provided. Scope for the future work has also been discussed.<br>AcSIR

The main aim of the work was to produce scale-up methods for the design of aerated stirred tanks using a combined computational fluid dynamics (CFD) and population balance approach. First a modeling study of single phase stirred tanks was performed to evaluate the best model features (turbulence model, impeller's model, discretisation, grid etc). Good agreement was obtained between the CFD simulation and the LDA measurement on the time-averaged mean velocities and turbulence quantities. The angle-resolved mean velocities and turbulence quantities were also predicted very well as were the power number and the positions of the vortex cores. The next stage involved the development of a population balance model (PBM) which was carried out first using a well-mixed single compartment implemented in MATLAB to reduce the modeling complexity. The algorithm was validated for various mechanisms, namely breakage, aggregation, nucleation and growth which have an analytical solution available from literature. Tests using realistic models for bubble coalescence and breakage were also carried out with the results showing a reasonable agreement with the Sauter mean bubble sizes obtained from empirical correlations. The algorithm also responded well to changes in the turbulence dissipation rate, the initial bubble size distribution and the local gas hold-up, which suggest that the final bubble size is not affected by the initial bubble size. A fully predictive model must combine both the fluid mechanics and bubble dynamics models which can be performed either by a four-way or three-way coupling simulation. The disadvantage of the latter is that is does not consider the effect of the bubble dynamics in- the two-phase modelling. A four-way coupling (CFD-PBM) method was carried out by implementing the PBM within the CFD code. Various drag models which take into account the effect of distorted bubbles and dense gas dispersion are also considered. Mass transfer models are also implemented using the bubble sizes obtained from the PBM. The CFD-PBM model showed a reasonable prediction of the power number, local bubble sizes, gas hold-up, dissolved oxygen concentration and the mean velocities of the two-phase flow in comparison to experimental data taken from the literature. Finally, the CFD-PBM model was employed to evaluate the consequences of scale-up on the mass transfer rate in aerated stirred tanks agitated either by Rushton turbine or CD-6 impeller with operating volume ranged from 14L to 1500L. Three scale-up rules, namely a constant P IV combined with either constant Fig, Vg and VVM were studied. The simulation results suggest, that a successful scale-up may be achieved by keeping the P IV and VVM constant, which led to a slightly higher (kLa) representing a more conservative approach. In contrast, constant P/V and Vg led to a slight reduction in the rate of mass transfer at larger scale which is in agreement with experimental measurement . from the literature. Results from the CFD-PBM simulation also suggest a similar scale-up rule may be applicable for an advanced gas dispersion impeller such as the CD-6 which yielded a similar scale-up trend to that of a Rushton turbine.

The present research describes an investigation of the flow through the inlet port and the cylinder of an internal combustion engine. The principal aim of the work is to interpret the effects of the port shape and valve lift on the engine's "breathing" characteristics, and to develop a better understanding of flow and turbulence behaviour through the use of Computational Fluid Dynamics (CFD), using a commercial available package STAR-CD. A complex computational mesh model was constructed, which presents the actual inlet port/cylinder assembly, including a curved port, a cylinder, moving valve and piston. Predictions have been carried out for both steady and transient flows. For steady flow, the influence of valve lift and port shape on discharge coefficient and the in-cylinder flow pattern has been examined. Surface static pressures predicted using the CFD code, providing a useful indicator of flow separation within the port/cylinder assembly, are presented and compared with experimental data. Details of velocity fields obtained by laser Doppler anemometry in a companion study at King's College London, using a steady flow bench test with a liquid working fluid for refractive index matching, compared favourably with the predicted data. For transient flow, the flow pattern changes and the turbulence field evolutions due to valve and piston movement are presented, and indicate the possible source of cyclic variability in an internal combustion engine.

Thesis (PhD)--Stellenbosch University, 2014.<br>ENGLISH ABSTRACT: A Computational Fluid Dynamics (CFD) model was developed for the prediction of flotation rate constants in a stirred flotation tank and validated against experimental data. The model incorporated local, time-varying values of the turbulent flow field into an existing kinetic flotation model based on the Generalised Sutherland Equation to predict the overall flotation rate constant. Simulations were performed for the flotation of various minerals at different operational conditions and the predictions were compared with experimental data. It was found that the CFD-based model yielded improvements in the prediction of flotation rate constant for a range of hydrophobicities, agitation speeds and gas flow rates compared with existing methodologies, which use volume-averaged empirical expressions for flow variables. Moreover, comparing to the available CFD alternatives for the flotation modelling this approach eliminates the need for solving an extra partial differential equation resulting in a more computationally economic model. The model was developed in three stages. In the first, a single-phase model was used to establish the requirements for successful modelling of the velocity components and turbulent properties of water inside flotation tanks. Also, a novel use of the Grid Convergence Index for this application was carried out, which allowed determination of the maximum achievable reduction in numerical uncertainties through systematic grid refinement and adaptation. All subsequent simulations were performed at the optimal discretization level determined in this manner. It was found that the Moving Reference Frames (MRF) method was adequate for representation of the impeller movement when the rotational zone was located close to the impeller, using a time step advance of between 10◦ and 15◦ of impeller rotation. Comparison of the different turbulence models for the single-phase modelling revealed that the standard k-e and Large Eddy Simulation turbulence models both performed equally well and that the computational requirement was lower for the standard k-e model, making it the method of choice. Validation of the methodology was done by comparison with experimental data for two different stirred tanks including an unbaffled mixer and a fully baffled standard Rushton turbine tank. The validation against experimental data showed that the model was capable of predicting the flow pattern, turbulent properties and the generation of trailing vortices. The second stage of modelling used an Eulerian-Eulerian formulation for gasliquid modelling of gas-sparged fully baffled vessels (2.25 l, 10 l and 50 l) using a Rushton turbine. It was determined that the minimum model uncertainty resulting from simulation of the sparger was achieved using a disk sparger with a diameter equal to 40% of the impeller diameter. The only significant interfacial force was found to be the drag force, and this was included in the multiphase methodology. A parametric study on the available formulations for the drag coefficient was performed which showed that the effect of turbulence on the air bubbles can accurately be represented using the proposed model of Lane (Lane, 2006). Validation of the methodology was conducted by comparison of the available experimental gas holdup measurements with the numerical predictions for three different scales of Rushton turbine tanks. The results verified that the application of the designed sparger in conjunction with Lane drag coefficient can yield accurate predictions of the gas-liquid flow inside the flotation tank with the error percentage less than 6%, 13%, and 23% for laboratory, pilot and industrial scale Rushton turbine tanks, respectively. The last stage of this study broadened the Eulerian-Eulerian framework to predict the flotation rate constant. The spatially and temporally varying flow variables were incorporated into an established fundamental flotation model due to Pyke (Pyke, 2004) based on the Generalized Sutherland equation for the flotation rate constant. The computation of the efficiency of the flotation sub-processes also incorporated the turbulent fluctuating flow characteristics. Values of the flotation rate constants were computed and volume-weight averaged for validation against available experimental data. The numerical predictions of the flotation rate constants for quartz particles for a range of particle diameters showed improvements in the predictions when compared with values determined from existing methodologies which use spatially uniform values for the important hydrodynamic variables as obtained from empirical correlations. Further validations of the developed CFD-kinetic model were carried out for the prediction of the flotation rate constants of quartz and galena floating under different hydrophobicities, agitation speeds and gas flow rates. The good agreement between the numerical predictions and experimental data (less than 12% error) confirmed that the new model can be used for the flotation modelling, design and optimization. Considering the limited number of CFD studies for flotation modelling, the main contribution of this work is that it provides a validated and optimised numerical methodology that predicts the flotation macro response (i.e., flotation rate constant) by integrating the significance of the hydrodynamic flow features into the flotation micro-processes. This approach also provides a more economical model when it is compared to the available CFD models for the flotation process. Such an approach opens the possibility of extracting maximum advantage from the computed parameters of the flow field in developing more effective flotation devices.<br>AFRIKAANSE OPSOMMING: 'n Wye verskeidenheid van industriële toepassings gebruik meganies geroerde tenks vir doeleindes soos die meng van verskillende vloeistowwe, verspreiding van 'n afsonderlike fase in 'n deurlopende vloeistoffase en die skeiding van verskillende komponente in ‘n tenk. Die hoofdoel van die tesis is om ‘n numeriese model te ontwikkel vir ʼn flotteringstenk. Die kompleksiteit van die vloei (drie-dimensioneel, veelvuldige fases en volledig turbulent) maak die voorspelling van die werksverrigting van die flottasieproses moeilik. Konvensioneel word empiriese korrelasies gebruik vir modellering, ontwerp en die optimalisering van die flotteringstenks. In die huidige studie word ‘Computational Fluid Dynamics’ (CFD) egter gebruik vir die modellerings doel, aangesien dit ‘n alternatief bied vir empiriese vergelykings deurdat dit volledig inligting verskaf aangaande die gedrag van vloei in die tenk. Die model is ontwikkel in drie agtereenvolgende stadiums. Dit begin met ‘n strategie vir enkelfase modellering in die tenk, vorder dan na ‘n gas-vloeistof CFD model en brei dan die tweede stap uit om ‘n CFD model te skep vir die skeidingsproses deur flottering. ‘n Enkelfase model, gebaseer op die kontinuïteits- en momentumvergelykings, dien as basis vir die flottasie model. Die ‘Multiple Reference Frames’ (MRF) metode word gebruik om die rotasie van die stuwer na te boots, terwyl die dimensies van die rotasie-sone gekies is om die gepaardgaande onsekerhede, insluitend die model- en numeriese foute veroorsaak deur die dimensies van die roterende sones, te verminder. Die turbulensie model studie het getoon dat die standaard k-e turbulensie model redelike akkuraatheid kon lewer in die numeriese voorspellings en die resultate verskil in gemiddeld net minder as 15% van die eksperimentele lesings, terwyl die rekenaartyd min genoeg was om die simulasies op 'n persoonlike rekenaar uit te voer. Verder het die ‘Grid Convergence Index’ (GCI) metode die inherente onsekerhede in die numeriese voorspellings gerapporteer en gewys dat die onderskatting van die turbulensie wat algemeen plaasvind reggestel kan word deur van ‘Large Eddie’ (LES) of ‘Direct Numerical Simulations’ (DNS) gebruik te maak. Die metode wat ontwikkel is, is op twee tipes geroerde tenks getoets, naamlik 'n onafgeskorte menger en 'n standaard Rushton turbine tenk. Die numeriese resultate is teen eksperimentele data gevalideer en het gewys dat die model in staat is om die vloeipatrone, turbulensie einskappe en die vorming van agterblywende vortekse te voorspel. Die CFD resultate het getoon dat die vloeipatroon twee simmetriese rotasies siklusse bo en onder die roterende sone vorm, terwyl die vlak van die ooreenkoms tussen die numeriese voorspellings van die turbulente eienskappe en die eksperimentele lesings met minder as 25% verskil. As die tweede stap van hierdie navorsing is 'n Eulerian-Eulerian struktuur ontwikkel vir die gas-vloeistof modellering binne 'n standaard Rushton turbine flotteringstenk. Soos vir die enkelfase modellering is die Reynolds spanningstensor opgelos deur die standaard k-e turbulensie model, terwyl die lugborrels ingevoer/versamel is in/van die tenk deurmiddel van bron/sink terme. Verskeie ‘sparger’ rangskikkings is in die tenk geïmplementeer om die onsekerheid in die model weens die metode van luginspuiting te verminder. Verder is verskillende korrelasies vir die sleursyfer vergelyk vir laminêre en turbulente vloei in die tenk. Daar is gevind dat die skyf ‘sparger’, met 'n deursnee gelykstaande aan 40% van die stuwer deursnee, in samewerking met die voorgestelde model van Lane (Lane, 2006) vir die bepaalde sleursyfer die naaste ooreenkoms met die eksperimentele metings lewer (met 'n gemiddelde verskil van minder as 25%). 'n Vergelykende studie is ook uitgevoer om die gevolge van die gas vloeitempo en roerspoed vir drie verskillende geroerde tenks met volumes van 2.5 l, 10 l en 50 l te ondersoek. Die resultate van hierdie afdeling bevestig dat die CFD metode in staat was om die gas-vloeistof vloei in die flotteringstenk korrek te voorspel. Die veelvuldigefase model wat ontwikkel is, is uitgebrei vir flottasie modellering. Dit behels die integrasie van die CFD resultate met die fundamentele flottasie model van Pyke (Pyke, 2004) vir die flotteringstempo konstant. Die CFD model is toegerus met Pyke se model deur aanvullende gebruiker gedefinieerde funksies. Die CFD-kinetiese model is geëvalueer vir die flottering van kwartsdeeltjies en die resultate het die geloofwaardigheid van die model bevestig, aangesien die gemiddelde verskil tussen die numeriese voorspellings vir die flotteringstempo konstante en die eksperimentele data minder as 5% was. Die resultate is ook vergelyk met die analitiese berekeninge van Newell en daar is bevind dat die model vergelykbare voorspellings van die flotteringtempo konstantes lewer, met die ‘root mean square deviations’ (RMSD) gelyk of minder as die RMSD waardes vir die analitiese berekeninge. Verdere ondersoeke van die CFD-kinetiese model bestaan uit 'n parametriese studie wat die gevolge van die roertempo, gas vloeitempo en die oppervlak hidrofobisiteit op die flottering van kwarts- en galenietdeeltjies bestudeer. Die aanvaarbare ooreenkoms tussen die numeriese voorspellings en eksperimentele data (oor die algemeen minder as 12% fout) bewys dat die nuwe model gebruik kan word vir flotterings modellering en optimalisering.

Defrosting in the refrigeration industry is used to remove the frost layer accumulated on the evaporators after a period of running time. It is one way to improve the energy efficiency of refrigeration systems. There are many studies about the defrosting process but none of them use computational fluid dynamics (CFD) simulation. The purpose of this thesis is (1) to develop a defrost model using the commercial CFD solver FLUENT to simulate numerically the melting of frost coupled with the heat and mass transfer taking place during defrosting, and (2) to investigate the thermal response of the evaporator and the defrost time for different hot gas temperatures and frost densities. A 3D geometry of a finned tube evaporator is developed and meshed using Gambit 2.4.6, while numerical computations were conducted using FLUENT 12.1. The solidification and melting model is used to simulate the melting of frost and the Volume of Fluid (VOF) model is used to render the surface between the frost and melted frost during defrosting. A user-defined-function in C programming language was written to model the frost evaporation and sublimation taking place on the free surface between frost and air. The model was run under different hot gas temperatures and frost densities and the results were analyzed to show the effects of these parameters on defrosting time, input energy and stored energy in the metal mass of the evaporator. The analyses demonstrate that an optimal hot gas temperature can be identified so that the defrosting process takes place at the shortest possible melting time and with the lowest possible input energy.

<p>Computational Fluid Dynamics is the analysis of a system involving fluid flow, heat transfer and associated phenomena such as chemical reactions by means of a computer-based simulation. The simulations in this study are performed using (CFD) software package FLUENT. The mixture of two gases (Silane gas (SiH4) and Hydrogen gas (H2)) are delivered into the hot-wire chemical vapor deposition system (HWCVD) with the two deposited substrates (glass and Silicon). This process is performed by the solar cells group of the Physics department at the University of the Western Cape. In this thesis, the simulation is done using a CFD software package FLUENT, to model the gas-flow patterns inside the HWCVD system. This will show how the gas-flow patterns are affected by the varying temperature of the heater in each simulation performed in this study under a constant pressure of 60&mu<br>Bar of the system.</p>

Conventional understanding of quality of energy suggests that heat is a low grade form of energy. Hence converting this energy into useful form of work was assumed difficult. However, this understanding was challenged by researchers over the last few decades. With advances in solar, thermal and geothermal energy harvesting, they believed that these sources of energy had great potential to operate as dependable avenues for electrical power. In recent times, waste heat from automobiles, oil and gas and manufacturing industries were employed to harness power. Statistics show that US alone has a potential of generating 120,000 GWh/year of electricity from oil , gas and manufacturing industries, while automobiles can contribute upto 15,900 GWh/year. Thermoelectric generators (TEGs) can be employed to capture some of this otherwise wasted heat and to convert this heat into useful electrical energy. This field of research as compared to gas turbine industry has emerged recently over past 30 decades. Researchers have shown that efficiency of these TEGs modules can be improved by integrating heat transfer augmentation features on the hot side of these modules. Gas turbines employ advanced technologies for internal and external cooling. These technologies have applications over wide range of applications, one of which is thermoelectricity. Hence, making use of gas turbine technologies in thermoelectrics would surely improve the efficiency of existing TEGs. This study makes an effort to develop innovative technologies for gas turbine as well as thermoelectric applications. The first part of the study analyzes heat transfer augmentation from four different configurations for low aspect ratio channels and the second part deal with characterizing improvement in efficiency of TEGs due to the heat transfer augmentation techniques.<br>Master of Science

Flue gas scrubbing devices are used to clean exhaust gas from industrial plants and play an important role in the drive to conserve the planet. Centrifugal wet scrubbers are one such type of widely used scrubbing device. Unfortunately, their design, which is often based on rules of thumb, can contribute to operational problems that are costly to rectify. This project employed experiments and computational fluid dynamics to develop an improved understanding of the flow processes inside a centrifugal wet scrubber and proposed design modifications for improved performance.

Thesis (MScEng)--Stellenbosch University, 2012.<br>ENGLISH ABSTRACT: The use of micro gas turbines (MGTs) for the propulsion of unmanned aerial vehicles (UAVs) has become an industry standard. MGTs offer better performance vs. weight than similar sized, internal combustion engines. The front component of an MGT serves the purpose of compressing air, which is subsequently mixed with a fuel and ignited to both power the turbine which drives the compressor, and to produce thrust. Centrifugal compressors are typically used because of the high pressure ratios they deliver per stage. The purpose of this project was to design a centrifugal compressor impeller, and to devise a methodology and the tools with which to perform the aforementioned. A compressor impeller adhering to specific performance and dimensional requirements was designed. The new compressor was designed using a mean-line performance calculation code. The use of the code was vindicated through comparison with the results from a benchmark study. This comparison included mean-line, Computational Fluid Dynamic (CFD), and experimental results: the new design mean-line results were compared to the results of CFD simulations performed on the same design. The new design was optimised using an Artificial Neural Network (ANN) and Genetic Algorithm. Prior to and during optimisation, the ANN was trained using a database of sample CFD calculations. A Finite Element Analysis (FEA) was done on the optimised impeller geometry to ensure that failure would not occur during operation. According to CFD results, the final design delivered good performance at the design speed with regards to pressure ratio, efficiency, and stall margin. The mechanical stresses experienced during operation were also within limits. Experimental results showed good agreement with CFD results of the optimised impeller. Keywords: micro gas turbine, centrifugal compressor, impeller, CFD, experimental, optimisation, FEA.<br>AFRIKAANSE OPSOMMING: Die gebruik van mikrogasturbines vir die aandrywing van onbemande vliegtuie het ‟n standaard geword in die industrie. Mikrogasturbines bied beter werkverrigting teen gewig as binnebrandenjins van soortgelyke grote. Hierdie eienskap verseker dat mikrogasturbines as aandryfmotors vir onbemande vliegtuie uiters voordelig is. Die voorste komponent van ‟n mikrogasturbine dien om lug saam te pers, wat dan met brandstof gemeng en daarna aan die brand gesteek word om krag aan die kompressor en stukrag te voorsien. Sentrifugaalkompressors word tipies gebruik as gevolg van die hoë drukverhoudings wat hierdie komponente per stadium kan lewer. Die doel van hierdie projek was om ‟n sentrifugaalkompressor te ontwerp, en ‟n metode en die hulpmiddels te ontwikkel om laasgenoemde uit te voer. ‟n Kompressor rotor wat voldoen het aan sekere werkverrigtings en dimensionele vereistes is ontwerp. Die nuwe kompressor rotor is met behulp van 1-dimensionele werkverrigting-berekeningskode ontwerp. Die berekeningsakkuraatheid van die kode en díé van ‟n kommersiële Berekenings Vloeidinamika pakket is bevestig deur die berekende resultate te vergelyk met die van eksperimente. Die nuwe rotor is gevolglik deur middel van ‟n Kunsmatige Neurale Netwerk en Genetiese Algoritme geoptimeer. Die Kunsmatige Neurale Netwerk is voor en gedurende optimering deur Berekenings Vloeidinamika simulasies opgelei. Die meganiese sterkte van die geoptimeerde rotor is nagegaan met behulp van ‟n Eindige Element Analise. Dit is gedoen om te verseker dat die rotor nie sal faal by die bedryfspunt nie. Berekenings Vloeidinamika resultate het getoon dat die finale rotor ontwerp ‟n goeie werkverrigting lewer by die ontwerpspoed, met betrekking tot drukverhouding, bennutingsgraad, en stakingsmarge. Eksperimentele resultate het goeie ooreenstemming met die Berekenings Vloeidinamika resultate van die geoptimeerde rotor getoon. Sleutelwoorde: mikrogasturbine, sentrifigaalkompressor, rotor, Berekenings Vloeidinamika, eksperimenteel, optimering, Eindige Element Analise.

This dissertation focuses on the development of computational tools capable of predicting the complex fluid dynamics behavior of industrial scale gas-liquid systems. In the past, the description of such systems for design purposes was performed through the use of correlations, formulated by means of very expensive experimental campaigns. The limits of this approach can be overcome by the use of modern simulation tools, such as Computational Fluid Dynamics (CFD). However the momentum and mass transfer description of gas-liquid systems is characterized by the intrinsic poly-dispersity of the gas phase, namely the different dispersed bubbles are usually distributed over a certain range of size, velocity and chemical composition values. Then a proper methodology must be applied to tackle this issue: Population Balance Modeling (PBM), originally formulated for crystallization problems, can be successfully adopted to describe any generic dispersed system in which the combination of different phenomena (i.e., physical space advection, diffusion, aggregation, breakage, growth, nucleation) determines the state of the dispersed system. All these considerations explain the interest of the multiphase flow community in efficient coupled PBM-CFD methods, especially when such methodologies are employed to investigate large scale systems with complex phenomena involved, such as mass transfer and chemical reactions. Moreover, the knowledge of more than one property of the disperse phase can be required to properly describe the problem (i.e., multivariate description instead of monovariate), as in the case of reacting multiphase systems, and this fact represents a challenge from the modeling point of view. At this point, it is very important to reduce the computational costs introduced by the Population Balance Equation (PBE), by recurring to approximate but reliable methods. In this sense, it is also recent the formulation of Quadrature-Based Moments Methods (QBMM) for particulate flows, a class of solution methods particularly suitable for the purposes of this work. Therefore in this dissertation the issues related to the application of these methods for the description of industrial scale bubble columns and aerated stirred tank reactors will be discussed. In the first part of this work, the derivation of PBE and the Eulerian-Eulerian methodology for gas-liquid systems is shown, especially concerning the description of the mass transfer problem in air-water system, in which the information on the bubble size distribution is needed to estimate the interfacial area and the distribution of bubble composition may be required to calculate the local mass transfer driving force. Moreover the QBMM solution methods, both for monovariate and multivariate cases, are here presented and discussed in detail. In the second part, a preliminary study of QBMM stability and accuracy for simplified zero-dimensional systems is performed through comparison with accurate PBE solution methods, then the implementation is verified through the simulation of one and two-dimensional systems in order to point out the numerical issues than may arise when physical space advection is considered. Eventually, the simulation of realistic gas-liquid systems (i.e., a stirred tank reactor and a bubble column), for which experimental data are available relating to the local bubble size distribution (BSD) and mass transfer, are performed for validation purposes. The shown results prove the effectiveness of the proposed PBM-CFD approach: in general a very good agreement with the experimental data is observed with a reasonable computational costs.

Thesis (M. S.)--Mechanical Engineering, Georgia Institute of Technology, 2008.<br>Committee Co-Chair: de Oliveira, Cassiano; Committee Co-Chair: Ghiaasiaan, S. Mostafa; Committee Member: Martineau, Richard C.; Committee Member: van Rooijen, W.F.G

Orientador: Sávio Souza Venâncio Vianna<br>Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Química<br>Made available in DSpace on 2018-08-26T16:12:11Z (GMT). No. of bitstreams: 1 FerreiraJunior_ElmodeSena_M.pdf: 18188081 bytes, checksum: 2b445e8828a2a2b90c9a27c3379a7d74 (MD5) Previous issue date: 2015<br>Resumo: A simulação numérica é de grande importância em diversas áreas da engenharia, tais como otimização e manutenção de processo químico, bem como na indústria do petróleo e segurança do processo. O Fire Dynamics Simulator (FDS) é um código de Fluidodinâmica Computacional com base na simulação das grandes escalas. Este foi desenvolvido pelo Instituto Nacional de Padrões e Tecnologia (NIST). O código FDS foi originalmente projetado para modelar baixo fluxo de velocidade comumente encontrados em cenários de incêndio. Assim, o FDS não é adequado para simulação de casos onde o número de Mach é elevado. Para superar esta limitação, este trabalho propõe um novo modelo dedicado às características próximas da saída do jato a fim de permitir o FDS simular cenários de jatos e dispersão de gás. A abordagem também reduz significativamente o tempo da simulação computacional. A ferramenta proposta é uma alternativa livre e confiável para a modelagem de dispersão de gás. Os resultados são amplamente discutidas e um estudo de caso de uma plataforma é apresentado. A comparação com os resultados experimentais, bem como um pacote CFD comercial mostram boa concordância<br>Abstract: The numerical simulation is of great importance in various areas of engineering such as optimization and maintenance of chemical process, petroleum industry and process safety. The Fire Dynamics Simulator (FDS) is a Computational Fluid Dynamics (CFD) code based on Large Eddy Simulation (LES) modeling and developed by National Institute of Standards and Technology (NIST). FDS code was originally designed to model low speed flow commonly found in fire scenarios. Hence, FDS is not suitable for modeling high Mach number cases. To overcome this limitation this work proposes a novel model dedicated to the near field jet characteristics in order to enable FDS to simulate jet scenarios and gas dispersion. The approach also reduces the computational time significantly as far as turbulent jet flows are concerned. The proposed tool is a free and reliable alternative for gas dispersion modeling. Results are extensively discussed and case study for a typical offshore site is presented. Comparison with experimental results as well as commercial CFD package show good agreement<br>Mestrado<br>Sistemas de Processos Quimicos e Informatica<br>Mestre em Engenharia Química

Induktiefgekoppelde-plasmareaktore (IGP’s) het toepassings in verskeie industrieë, insluitend die voorbereiding van metaalpoeiers vir laagvervaardiging. Die skermgas (ook skutgas gnoem) speel ’n belangrike rol in die termiese afskerming van die reaktorwand in ’n IGP. Die energie wat verloor word deur die wand van die reaktor kan verminder word deur die hittesone weg van die wand af te beweeg. Hierdie verplasing van die hittesone word bereik deur ’n skermgas te gebruik wat moeiliker ioniseer as die plasmagas. Die ioniseringsgraad van waterstof is laer as dié van argon weens die hoër elektriese geleidingsvermoë van argon by soortgelyke temperature. Waterstof word dus in klein hoeveelhede in die skutgas gebruik met argon as die hoof bestandeel en hoofplasmagas. Die waterstof voorkom dus plasmavorming naby die wand. Die skutgas het ook ’n heelwat hoër vloeisnelheid en verminder sodoende die beskikbare tyd vir hitte-oordrag na die wand. Die besondere hoë temperature wat in ’n IGP bereik word, belemmer egter die meting van eenvoudige lesings soos vloeisnelheid en temperatuur. Rekenaarmodelle voorsien ons van die geleentheid om die fisiese en chemiese eienskappe van ’n plasma te ondersoek asook die nodige gereedskap om die gedrag van die plasma te analiseer sonder eksperimentele lesings. Daar is verskeie numeriese modelle van IGP-sisteme in die literatuur alhoewel nie een van dié modelle die effek van die skutgassamestelling in ag neem nie. Die hoeveelheid waterstof in die skutgas kan groot newe-effekte hê op die plasmagas a.g.v. die hoër ionisasiepotensiaal van waterstof. ’n Oormaat waterstof in die skutgas is ook ’n verkwisting van voermateriaal. Albei die faktore het ’n invloed op die ekonomiese uitvoerbaarheid van die plasmaproses. Hierdie navorsing het beoog om die optimale skutgassamestelling te vind vir die reaktor wat by Necsa gebruik word vir sferoïedisering. Die werk is uitgevoer met die kommersiële eindige-elementsagtewarepakket COMSOL Multiphysics R. Hierdie rekenaarmodel dui daarop dat die wand beskerm kan word van plasmavorming met ’n waterstof/argon skutgas wat sodoende ook die energieverliese deur die wand verminder. Waterstof verbeter die skutgas se hitte-oordragvermoë, maar verskuif die hittesone weg van die wand af. As gevolg van hierdie twee kompeterende meganismes bestaan daar ’n optimale bedrywingspunt by 3 vol% H2 in die skutgas. Die model is bevestig deur die energiebalans van die model te vergelyk met eksperimentele resultate.<br>Dissertation (MEng)--University of Pretoria, 2020.<br>Advanced Metals Initiative Suid Afrikaanse Akademie vir Wetenskap en Kuns<br>Chemical Engineering<br>MEng<br>Unrestricted

The growing need for increased performance from gas turbines has fueled the drive to raise turbine inlet temperatures. This results in high thermal stresses especially along the first stage nozzle guide vane cascade as the hot combustion products exiting modern day gas turbine combustors generally reach temperatures that could endanger the structural stability of these vanes and greatly reduce the vane life. The highest heat transfer coefficients in the vane passage occurs near the endwall, particularly in the leading edge-endwall junction where vortical flows cause the flow of hotter fluid in the mainstream to mix with relatively lower temperature boundary layer fluid. This work documents the computational investigation of air injection at the end wall through a cylindrical hole placed upstream of the nozzle guide vane leading edge-end wall junction. The effect of the secondary jet on the formation of the leading edge horseshoe vortex and the consequent formation of the passage vortex has been studied. For the computations, the Reynolds averaged Navier–Stokes (RANS) equations were solved with the commercial software ANSYS Fluent using the SST k-ω model. Total pressure loss coefficient and kinetic energy loss Coefficient contour plots at the exit of the cascade to estimate the effect of the endwall fluid injection on loss profiles at the vane cascade exit. Swirling strength contours were plotted at several axial chord locations in order to track the path of the passage vortex in and downstream of the vane cascade. Two different hole-positions (located at 1 hole diameter and 2 hole diameters from the leading edge) along a plane parallel to the incident flow were considered in order to study the effect of the hole position with respect to the vane leading edge-endwall junction. Three different streamwise hole inclination angles with respect to the mainstream flow direction were studied to identify the best angle for the injection of fluid through the endwall. This angle was combined with five different compound angles (0°, 30°, 45°, 60° and 90°) in order to study the effect of varying the compound angle on the leading edge vortex and the passage vortex. Each of the above studies were conducted at two different injected fluid-to-mainstream mass flow ratios (0.5% and 1%) in order to study the effect of varying injected flow rate on the formation of the leading edge vortex and the vane passage vortex. From the results it was observed that suitable selection of the secondary injection mass flow rate, injection angle and hole-position caused an absence of the leading edge horseshoe vortex and delayed migration of the passage vortex across the guide vane passage. Heat Transfer studies were also conducted to observe the absence/weakening of the leading edge vortex and the delayed pitch-wise movement of the passage vortex.<br>Master of Science

Le développement d'une nouvelle classe de molécules calorifères, déposées directement sur les plantes, est une nouvelle stratégie pour étendre les lieux propices à l'agriculture à des altitudes plus élevées, en prévenant les dommages causés par le froid. L'idée sous-jacente est que ces molécules calorifères sont capables d'absorber le rayonnement UV-visible et de le convertir en chaleur, dans ce cas, à destination de la surface des feuilles. Inspirés par les stratégies photoprotectrices efficaces trouvées dans la nature, nous étudions des dérivés du malate de sinapoyle (SM). Après absorption de la lumière, ces dérivés présentent une désexcitation non radiative rapide et efficace. D'autre part, les dicétopyrrolopyrroles sont également des candidats. Le dimère possède un état doublement excité de faible énergie qui n'est pas accessible au monomère, permettant à la conversion interne de se produire en premier. Nous caractérisons la fonction d'onde de l'état doublement excité en modifiant de façon systématique les dérivés de façon à ajuster la taille du système π et les caractères de l'accepteur et du donneur. Cette analyse ouvre de nouvelles voies pour contrôler l'équilibre entre la luminescence et la conversion interne dans de tels systèmes. Cependant, une caractérisation correcte des états doublement excités reste un défi : il n'existe aucun schéma de classification rigoureux et transférable entre les méthodes. Nous proposons donc de classer les états doublement excités selon deux cas limites : les états doublement excités à couche ouverte ou fermée. Notre schéma de classification est basé sur des descripteurs extraits des matrices de la densité<br>Developing a new class of molecular heaters to be applied in plants is a new strategy to extend locations suitable for agriculture to higher altitudes, preventing damages caused by the cold. The underlining idea is that molecular heaters can absorb UV-vis radiation and convert it into heat, in this case, to the leaves' surface. Inspired by nature and its efficient photoprotective features, we study the photophysics of derivatives of sinapoyl malate (SM). These derivatives exhibit a fast and efficient nonradiative decay through a twisted charge-transfer state. Another class of potential candidates as molecular heaters are the diketopyrrolopyrroles. The dimer has a low-lying doubly excited state that is not energetically accessible to the monomer, and this delays the fluorescence allowing internal conversion to occur first. We characterize the doubly excited state wavefunction by systematically changing the derivatives to tune the pi-scaffold size and the acceptor and donor characters. This analysis opens new ways to control the balance between luminescence and internal conversion in such systems. However, a proper characterization of doubly excited states is still a challenge, and no rigorous and transferable classification scheme between methods exists. Then, we propose classifying doubly excited states according to two limiting cases: the open- and closed-shell doubly excited states, based on descriptors extracted from density matrices

This study involves the modeling of small cold-gas (N2) thrusters nozzle and plume flows, their interactions with spacecraft surfaces and the induced pressure environment. These small cold-gas thrusters were used for pitch, yaw and roll control and were mounted on the bottom of the conical Environmental Monitor Payload (EMP) suborbital spacecraft. The pitch and yaw thrusters had 0.906 mm throat diameter and 4.826 mm exit diameter, while the roll thrusters had 1.6 mm throat diameter and 5.882 mm exit diameter. During thruster firing, at altitudes between 670 km and 1200 km, pressure measurements exhibited non-periodic pulses (Gatsonis et al., 1999). The pressure sensor was located inside the EMP and was connected to it's sidewall with a 0.1-m long, 0.022-m diameter tube and the pressure pulses appeared instantaneously with the firings for thrusters without a direct line-of-sight with the sensor entrance. Preliminary analysis showed that the plume of these small EMP thrusters undergoes transition from continuous to rarefied. Therefore, nozzle and plume simulations are performed using a combination of Navier-Stokes and Direct Simulation Monte Carlo codes. This study presents first a validation of the Navier-Stokes code Rampant used for the continuous EMP nozzle and plume simulations. The first Rampant validation example involves a two-dimensional axisymetric freejet expansion and is used to demonstrate the use of Bird's breakdown parameter. Results are compared favorably with those of Bird (1980) obtained through the method of characteristics. The second validation example involves three-dimensional plume simulations of a NASA thruster. This nitrogen nozzle has a throat diameter of 3.18 mm, an exit diameter of 31.8 mm, half-angle of 20 degrees, stagnation temperature of 699 K, stagnation pressure of 6,400 Pa. Simulation results are compared favorably with previous Navier-Stokes and Direct Simulation Monte Carlo numerical work. The third validation example involves three-dimensional simulations of Rothe's (1970) nozzle that has a throat diameter of 2.5 mm, an exit diameter of 20.3 mm, half-angle of 20 degrees, operating at stagnation temperature of 300 K and pressure of 1975 Pa. Numerical results also compared favorably to experimental data. The combined Navier-Stokes/DSMC approach and the EMP simulation results are presented and discussed. The continuous part of the EMP nozzle and plume flow is modeled using the three-dimensional Navier-Stokes Rampant code. The Navier-Stokes domain includes the geometry of the nozzle and the EMP base until transition of the continuous flow established by Bird's breakdown parameter. The rarefied part of the plume flow is modeled using the Direct Simulation Monte Carlo code DAC. Flowfield data obtained inside the breakdown surface from the Navier-Stokes simulation are used as inputs to the DSMC simulations. The DSMC domain includes the input surface and the EMP spacecraft geometry. The combined Navier-Stokes/DSMC simulations show the complex structure of the plume flow as it expands over the EMP surfaces. Plume reflection and backflow are demonstrated. The study also summarizes findings presented by Gatsonis et al. (2000), where the DSMC predictions at the entrance of the pressure sensor are used as inputs to a semi-analytical model to predict the pressure inside the sensor. It is shown that the pressure predictions for the pitch/yaw thrusters are close to the measurements. The plume of a pitch or yaw thruster reaches the pressure sensor after expanding on the EMP base. The pressure predicted for the roll thruster is larger that the measured. This is attributed to the uncertainty in the roll thruster location on the EMP base resulting, in the simulation, in a component of direct flow to the sensor.

This thesis aims to explore the potential for using large eddy simulation (LES) as a predictive tool for gas-turbine compressor flows. Compressors present a significant challenge for the Reynolds Averaged Navier-Stokes (RANS) based CFD methods commonly used in industry. RANS models require extensive calibration to experimental data, and thus cannot be used predictively. This thesis explores how LES can offer a more predictive alternative, by exploring the sensitivity of LES to sources of uncertainty. Specifically, the importance of the numerical scheme, the Sub-Grid Scale (SGS) model, and the correct specification of inflow turbulence is examined. The sensitivity of LES to the numerical scheme is explored using the Taylor-Green vortex test case. The numerical smoothing, controlled by a user defined smoothing constant, is found to be important. To avoid tuning the numerical scheme, a locally adaptive smoothing (LAS) scheme is implemented. But, this is found to perform poorly in a forced isotropic turbulence test case, due to the intermittency of the dispersive error. A novel scheme, the LAS with windowing (LASW) scheme, is thus introduced. The LASW scheme is shown to be more suitable for predictive LES, as it does not require tuning to a known solution. The LASW scheme is used to perform LES on a compressor cascade, and results are found to be in close agreement with direct numerical simulations. Complex transition mechanisms, combining characteristics of both natural and bypass modes, are observed on the pressure surface. These mechanisms are found to be sensitive to numerical smoothing, emphasising the importance of the LASW scheme, which returns only the minimum smoothing required to prevent dispersion. On the suction surface, separation induced transition occurs. The flow here is seen to be relatively insensitive to numerical smoothing and the choice of SGS model, as long as the Smagorinsky-Lilly SGS model is not used. These findings are encouraging, as they show that, with the LASW scheme and a suitable SGS model, LES can be used predictively in compressor flows. In order to be predictive, the accurate specification of inflow conditions was shown to be just as important as the numerics. RANS models are shown to over-predict the extent of the three dimensional separation in the endwall - suction surface corner. LES is used to examine the challenges for RANS in this region. The LES shows that it is important to accurately capture the suction surface transition location, with early transition leading to a larger endwall separation. Large scale aperiodic unsteadiness is also observed in the endwall region. Additionally, turbulent anisotropy in the endwall - suction surface corner is found to be important. Adding a non-linear term to the RANS model leads to turbulent stresses that are in better agreement with the LES. This results in a stronger corner vortex which is thought to delay the corner separation. The addition of a corner fillet reduces the importance of anisotropy, thereby reducing the uncertainty in the RANS prediction.

Hot isostatic pressing (HIP) is a thermal treatment method that is used to consolidate, densify or bondcomponents and materials. Argon gas is commonly used as the pressure medium and is isostaticallyapplied to the material with an excess pressure of 500-2000 bar and a temperature of 500-2200oC. WithHIP treatment being a well-established technology for the last decades, one is now striving to obtain anincreased understanding of local details in the internal gas flow and heat flux inside the HIP apparatus.The main objective of this work is to assess the potential of using computational fluid dynamics (CFD) asa reliable tool for future HIP development. Two simulations are being performed of which the first one isa steady-state analysis of a phase in the HIP-cycle called sustained state. The second simulation is atransient analysis, aiming to describe the cooling phase in the HIP-cycle. The most suitable modelingapproaches are determined through testing and evaluation of methods, models, discretization schemes andother solver parameters. To validate the sustained state simulation, the solution is compared tomeasurements of operating pressure, heat dissipation rate out through the HIP vessel and localtemperature by the vessel wall. However, no validation of the cooling simulations has been conducted. Asensitivity analysis was also performed, from which it could be established that a mesh refinement ofstrong temperature gradients resulted in an increase of wall heat dissipation rate by 1.8%. Both of thesimulation models have shown to yield satisfactory solutions that are consistent with the reality. With theachieved results, CFD has now been introduced into the HIP field and the presented modeling methodsmay serve as guidelines for future simulations.

This work presents the result achieved through investigation of RH-2 gas-lift valve dynamic performance. It is an unbalanced gas-lift valve injection pressure operated, for high injection pressure applications. First, a CFD model was developed in order to obtain the valve orifice flow pattern performance curve. The CFD curve was compared with the curve experimentally obtained, conceiving very promising results. A test bench, and the necessary test devices, have been projected and built looking forward to determine the bellows load rate. Second, a CFD mesh deformation model was developed, which allowed the determination of dynamic performance curves on orifice, transition and throttling flow patterns for a given bellows pressure. The accuracy of the mesh deformation model was verified comparing the obtained curve with experimental results. The results of numerous CFD model simulations allowed to correlate data and to find a transition pressure, the production pressure for the maximum gas throughput and the product of the discharge coefficient by the expansion factor. The mathematical model developed allows predicting the gas throughput capacity of the gas-lift valve using injection pressure, production pressure and bellows pressure, for a defined load rate and a defined port diameter.<br>Nos primeiros estágios de produção, um poço de petróleo apresenta um fluxo natural, sendo a energia necessária para elevação dos fluidos até a superfície fornecida pelo próprio reservatório. Neste caso, diz-se que o poço é surgente. Entretanto, na medida em que as reservas são produzidas, a pressão do reservatório diminui e surge a necessidade de complementar artificialmente a energia requerida para a elevação. Diz-se, então, que o poço produz por elevação artificial. De todos os métodos de elevação artificial, o gas lift é o mais amplamente utilizado, e para a sua implementação são requeridas as chamadas válvulas de gas lift. O conhecimento do comportamento dinâmico da válvula de gas lift é fundamental na etapa de projeto e no estabelecimento de estratégias operacionais eficientes. Este trabalho apresenta os resultados obtidos no estudo do desempenho dinâmico da válvula de gas-lift RH-2, a qual consiste em uma válvula de gas lift não balanceada operada por pressão e de alta pressão de carregamento no fole, fabricada pela Weatherford, e que não dispõe de um modelo para o levantamento de suas curvas de desempenho dinâmico. Inicialmente, foi desenvolvido um modelo fluidodinâmico utilizando-se Dinâmica de Fluidos Computacional (CFD) para a obtenção da curva de desempenho no regime de orifício e este foi comparado com dados obtidos experimentalmente, produzindo resultados muito promissores. Uma bancada de testes com os dispositivos necessários foi projetada e construída para o levantamento da taxa de carga do fole. A seguir, foi desenvolvido um modelo fluidodinâmico da válvula no aplicativo CFX, utilizando uma malha deformável, que permitiu a geração das curvas de desempenho nos regimes de orifício, transição e estrangulamento para uma dada pressão de carregamento do fole. A precisão da malha deformável foi verificada comparando a curva obtida para diversas posições da haste com resultados experimentais. Os resultados das várias simulações do modelo fluidodinâmico permitiram correlacionar dados e calcular a pressão de transição, a pressão de produção onde ocorre a vazão máxima e o produto do coeficiente de descarga pelo fator de expansão. O modelo matemático desenvolvido permite predizer a vazão de gás que escoa pela válvula de gas lift a partir da pressão de injeção, da pressão de produção e da pressão de carregamento no fole, para uma taxa de carga do fole e um diâmetro de porta definidos.

The impact phenomena of high velocity micron-size particles, although commonly considered and described as detrimental in numerous engineering applications, can be used in a beneficial way if properly understood and controlled. The Cold Gas Dynamic Spray (CGDS) process, known as a surface modification, repair and additive manufacturing process, relies on such high velocity impacts. In the process, solid particles are accelerated by a supersonic gas flow to velocities up to 1200 m/s and are simultaneously heated to temperatures lower than their melting point. When propelled under proper velocity and temperature, the particles can bond onto a target surface. This bonding is caused by the resulting interfacial deformation processes occurring at the contact interface. Hence, the process relies heavily on the gas/particle and particle/substrate interactions. Although numerous experimental and/or numerical studies have been performed to describe the phenomena occurring during particle flight and impact in the CGDS process, numerous phenomena remain poorly understood. First, the effect of substrate surface topographical condition on the particle deformation and ability to successfully adhere, i.e. atomically and/or mechanically, has not been thoroughly investigated such that its influence is not well understood. Another aspect of the process that is generating the largest gap between experimental and numerical studies in the field is the lack of particle in-flight temperature measurements. Obtaining such data has proven to be technically difficult. The challenges stem from the short particle flight time, low particle temperature and small particle size preventing the use of established thermal spray pyrometry equipment. Relatedly, lack of such measurements precludes a proper experimental study of the impact related phenomena at the particle/substrate interface. As a result, the effect of particle size dependent temperature on overall coating properties and atomic bonding relies currently on estimates. Finally, the effect of particle impact characteristics on interfacial phenomena, i.e. grain size and geometry, velocity/temperature, and oxide scale thickness, on adhesion and deformation upon single particle collision has also been scarcely studied for soft particle depositions on hard substrate. Hence, the current research work aims at studying fundamental aspects of particle/gas heat transfer and particle/substrate impact features in goals to improve the understanding of the CGDS process. Different surface preparation methods will be used to create various surface roughness and topographical features, to provide a clear understanding of the target surface state influence on coating formation and adhesion. Additionally, new equipment relying on novel technology, i.e. high-speed IR camera, will be utilized to obtain particle in-flight temperature readings with sequence recordings. Subsequently, the experimental particle in-flight temperature readings will be used to develop a computational fluid dynamics model in goals to validate currently used Nusselt number correlations and heat transfer equations. The particle size-dependent temperature effect on the particle’s elastic and plastic response to its impact with a targeted surface and its ability to successfully bond and form a coating will be studied experimentally. A thorough CFD numerical work, based on experimental findings, will be included to provide full impact characteristics (velocity, temperature, size and trajectory) of successfully deposited particles. Finally, the numerical results will be utilized in the ensuing study to correlate single particle deformation, adhesion and interfacial features to impact characteristics. A finite element model will be included to investigate the effect of particle size dependent temperature on single particle interfacial pressure, temperature and bonding ability.

This thesis is a computational study of circumstellar gas disks, with a special focus on modeling techniques and on numerical methods not only as scientific tools but also as a target of study. In particular, in-depth discussions are included on the main numerical strategy used, namely the moving-mesh method for astrophysical hydrodynamics. In this work, the moving-mesh approach is used to simulate circumstellar disks for the first time.<br>Astronomy

The premise of the work presented here is to use a common analytical tool, Computational Fluid dynamics (CFD), along with a difference turbulence models. Eddy viscosity models as well as state-of-the-art Large Eddy Simulation (LES) were used to study the flow past bluff bodies. A suitable CFD code (CFX5.6b) was selected and implemented. Simulation of turbulent transport for the gas through the gaps of the randomly distributed spherical fuel elements (pebbles) was performed. Although there are a number of numerical studies () on flows around spherical bodies, none of them use the necessary turbulence models that are required to simulate flow where strong separation exists. With the development of high performance computers built for applications that require high CPU time and memory; numerical simulation becomes one of the more effective approaches for such investigations and LES type of turbulence models can be used more effectively. Since there are objects that are touching each other in the present study, a special approach was applied at the stage of building computational domain. This is supposed to be a considerable improvement for CFD applications. Zero thickness was achieved between the pebbles in which fission reaction takes place. Since there is a strong pressure gradient as a result of high Reynolds Number on the computational domain, which strongly affects the boundary layer behavior, heat transfer in both laminar and turbulent flows varies noticeably. Therefore, noncircular curved flows as in the pebble-bed situatio n, in detailed local sense, is interesting to be investigated. Since a compromise is needed between accuracy of results and time/cost of effort in acquiring the results numerically, selection of turbulence model should be done carefully. Resolving all the scales of a turbulent flow is too costly, while employing highly empirical turbulence models to complex problems could give inaccurate simulation results. The Large Eddy Simulation (LES) method would achieve the requirements to obtain a reasonable result. In LES, the large scales in the flow are solved and the small scales are modeled. Eddy viscosity and Reynolds stress models were also be used to investigate the applicability of these models for this kind of flow past bluff bodies at high Re numbers.

The safety of migrating salmon, especially salmonids, in the Pacific Northwest has been a concern for decades. With the advent of fish bypass systems, and safer turbines the focus of salmon safety has turned to total dissolved gases. Produced by entrainment of air into tailrace waters, total dissolved gases (TDG) can cause gas bubble disease, a harmful and potential lethal disease in fish. Avian predators are another danger for migrating salmon. In some areas of the world birds common in the Pacific Northwest can account for as much as 65% of salmon smolt losses. The goal of this thesis is to determine the effects of changing operational conditions at McNary dam on fish exposure to predator habitats and TDG. Computational fluid dynamic models were implemented to predict the hydrodynamics, TDG distribution and inert particle trajectories in the tailrace of McNary dam for varying operational conditions. A 3D volume of fluid (VOF) model was used first to capture the free surface shape in the tailrace. A rigid-lid model was then used to simulate the hydrodynamics and TDG distribution within the tailrace using the free surface shape from the VOF model. This 3D two phase model utilized an anisotropic Reynolds Stress turbulence model. All grids were generated using the commercial Gridgen software. A lagrangian particle tracking model that followed Newton's laws of motion were used to track inert particles throughout the domain. Validation of the model was performed. A grid refinement study with four different refinement levels was performed. Velocities for each grid type were compared against field data taken in 2004, and TDG was compared amongst the four grids. It was determined the medium level of refinement could accurately predict the velocities, and the TDG was relatively independent of grid density; TDG averages at the grid outlets were within 1.435% of one another. The TDG distribution was then compared, using the grid of medium refinement against field data measured in 1997and were between 1.5 and 3% of error depending on the transect. After validation of the model 16 predictive simulations were run with varying levels of total river flow and operational conditions. Tailrace hydrodynamics along with TDG production and distribution were compared for simulations with comparable total river flow rates. Fish trajectories were tracked using the particle tracking model. Inert particles were injected into the domain and properties such as velocity, distance to the shore and depth about each were recorded. Statistics were then generated for the particles based on criteria that defined dangerous predation zones within the tailrace. After completion of the simulations, it was determined that existing operations consistentlyproduced higher levels of TDG due to increased entrainment of the powerhouse flows into the spillway regions. It was also found that with increasing total river flows, TDG levels increased. On average, summer operations had lower TDG than spring due to the lower total river flows. Predation zones were similar for all simulations, but particle statistics varied depending on operational conditions. In general, particles were safer for higher flowrates as fewer low velocity eddies where particles could be trapped formed in simulations with high flowrates.

The modern gas turbine engine industry needs a simpler and faster method to facilitate the design of gas turbine combustors due to the enormous costs of experimental test rigging and detailed computational fluid dynamics (CFD) simulations. Therefore, in the initial design phase, a couple of preliminary designs are conducted to establish initial values for combustor performance and geometric characteristics. In these preliminary designs, various one-dimensional models using analytical and empirical formulations may be used. One of the disadvantages of existing models is that they are typically geometric dependant, i.e. they apply only to the geometry they are derived for. Therefore the need for a more versatile design tool exists. In this work, which constitutes the first step in the development of such a versatile design tool, a single equation-set network simulation model to describe both steady state compressible and incompressible isothermal flow is developed. The continuity and momentum equations are solved through a hybrid type network model analogy which makes use of the SIMPLE pressure correction methodology. The code has the capability to efficiently compute flow through elements where the loss factor K is highly flow dependant and accurately describes variable area duct flow in the case of incompressible flow. The latter includes ducts with discontinuously varying flow sectional areas. Proper treatment of flow related non-linearities, such as flow friction, is facilitated in a natural manner in the proposed methodology. The proposed network method is implemented into a Windows based simulation package with a user interface. The ability of the proposed method to accurately model both compressible and incompressible flow is demonstrated through the analyses of a number of benchmark problems. It will be shown that the proposed methodology yields similar or improved results as compared to other’s work. The proposed method is applied to a research combustor to solve for isothermal flows and flow splits. The predicted flows were in relatively close agreement with measured data as well as detailed CFD analysis.<br>Dissertation (MEng (Mechanical Engineering))--University of Pretoria, 2005.<br>Mechanical and Aeronautical Engineering<br>unrestricted