Dissertations / Theses on the topic 'Integrated Computational Fluid Dynamics (CFD)'

An important aspect in the process of architectural design is the testing of solution alternatives in order to evaluate them on their appropriateness within the context of the design problem. Computational Fluid Dynamics (CFD) analysis is one of the approaches that have gained popularity in the testing of architectural design solutions especially for purposes of evaluating the performance of natural ventilation strategies in buildings. Natural ventilation strategies can reduce the energy consumption in buildings while ensuring the good health and wellbeing of the occupants. In order for natural ventilation strategies to perform as intended, a number of factors interact and these factors must be carefully analysed. CFD simulations provide an affordable platform for such analyses to be undertaken. Traditionally, these simulations have largely followed the direction of Best Practice Guidelines (BPGs) for quality control. These guidelines are built around certain simplifications due to the high computational cost of CFD modelling. However, while the computational cost has increasingly fallen and is predicted to continue to drop, the BPGs have largely remained without significant updates. The need to develop a CFD simulation framework that leverages the contemporary and anticipates the future computational cost and capacity can, therefore, not be overemphasised. When conducting CFD simulations during the process of architectural design, the variability of the wind flow field including the wind direction and its velocity constitute an important input parameter. Presently, however, in many simulations, the wind direction is largely used in a steady state manner. It is assumed that the direction of flow downwind of a meteorological station remains constant. This assumption may potentially compromise the integrity of CFD modelling as in reality, the wind flow field is bound to be dynamic from place to place. In order to improve the accuracy of the CFD simulations for architectural design, it is therefore necessary to adequately account for this variability. This study was a two-pronged investigation with the ultimate objective of improving the accuracy of the CFD simulations that are used in the architectural design process, particularly for the design and analysis of natural ventilation strategies. Firstly, a framework for integrated meso-scale and building scale CFD simulations was developed. Secondly, the newly developed framework was then implemented by deploying it to study the variability of the wind flow field between a reference meteorological station, the Virginia Tech Airport, and a selected localized building scale site on the Virginia Tech campus. The findings confirmed that the wind flow field varies from place to place and showed that the newly developed framework was able to capture this variation, ultimately, generating a wind flow field characterization representative of the conditions prevalent at the localized building site. This framework can be particularly useful when undertaking de-coupled CFD simulations to design and analyse natural ventilation strategies in the building design process.
Doctor of Philosophy
The use of natural ventilation strategies in building design has been identified as one viable pathway toward minimizing energy consumption in buildings. Natural ventilation can also reduce the prevalence of the Sick Building Syndrome (SBS) and enhance the productivity of building occupants. This research study sought to develop a framework that can improve the usage of Computational Fluid Dynamics (CFD) analyses in the architectural design process for purposes of enhancing the efficiency of natural ventilation strategies in buildings. CFD is a branch of computational physics that studies the behaviour of fluids as they move from one point to another. The usage of CFD analyses in architectural design requires the input of wind environment data such as direction and velocity. Presently, this data is obtained from a weather station and there is an assumption that this data remains the same even for a building site located at a considerable distance away from the weather station. This potentially compromises the accuracy of the CFD analyses as studies have shown that due to a number of factors such the urban built form, vegetation, terrain and others, the wind environment is bound to vary from one point to another. This study sought to develop a framework that quantifies this variation and provides a way for translating the wind data obtained from a weather station to data that more accurately characterizes a local building site. With this accurate site wind data, the CFD analyses can then provide more meaningful insights into the use of natural ventilation in the process of architectural design. This newly developed framework was deployed on a study site at Virginia Tech. The findings showed that the framework was able to demonstrate that the wind flow field varies from one place to another and it also provided a way to capture this variation, ultimately, generating a wind flow field characterization that was more representative of the local conditions.

The client-server architecture of STAR-CCM+ allows multiple users to collaborate on a simulation set-up. The effectiveness of collaboration with this architecture is tested and evaluated on five models. The testing of these models is a start to finish set-up of an entire simulation excluding computational time for generating mesh and solving the solution. The different models have distinct differences which test every operation that would be used in a general CFD simulation. These tests focus on reducing the time spent preparing the geometry to be meshed, including setting up for a conformal mesh between multiple regions in conjugate heat transfer models. Results from these five tests show a maximum speed up of 36%.

Dust generation at an underground coal mine working face continues to be a health and safety issue. Prolonged exposure to high concentrations of airborne respirable dust can cause a debilitating and often fatal respiratory disease called Black Lung. In addition, the deposition of float dust in mine return airways poses a serious safety hazard if not sufficiently diluted with inert rock dust. A localized methane explosion can transition into a self-propagating dust explosion. Since dust is a byproduct of various mining activities, such as cutting and loading, crushing, and transportation, the dust-related issues cannot be totally eliminated. However, the adverse health effects and safety concerns can be minimized if a significant amount of the generated dust is removed from the ventilation air by a mechanical device, such as a dust scrubber. Over the last three decades, flooded-bed dust scrubbers integrated into continuous miners have been successfully applied for capturing and removing airborne dust generated at the working face. According to the National Institute for Occupational Safety and Health (NIOSH), a flooded-bed scrubber can achieve more than 90% capture and cleaning efficiencies under optimum conditions. Although flooded-bed scrubbers have proven useful in the vast majority of cases, they have not yet been successfully applied to a longwall face. In the United States, numerous attempts have been made to reduce dust concentration at a longwall face through the application of a scrubber; but, none were successfully implemented. Encouraged by the successful use of a flooded-bed scrubber system at continuous miner faces, this research revisits the flooded-bed scrubber concept for a longwall shearer. For this investigation, a full-scale physical model of a Joy 7LS longwall shearer, modified with an integrated flooded-bed dust scrubber, was designed and fabricated at the University of Kentucky. The scope of work for this research was limited to capturing and cleaning dust generated near the shearer headgate drum only. The mock-up was transported to, and assembled in, the full-scale longwall dust gallery at the NIOSH Pittsburgh Research Laboratory (PRL). Tests were conducted to examine: (1) the effect of the scrubber on headgate-drum dust reduction and (2) the combined effect of the scrubber and splitter sprays on headgate drum dust reduction. Analysis of test results for the scrubber-alone condition indicates a significant dust reduction of up to 57% in the return airway and 85% in the test gallery walkway, whereas the combination of scrubber and splitter-arm sprays shows dust reduction of up to 61% and 96% in the return and walkway, respectively. These results indicate that a flooded-bed scrubber integrated into a longwall shearer can be used as a viable technique to reduce a large portion of airborne dust at a longwall face. Subsequently, a Computational Fluid Dynamics (CFD) model of the longwall gallery and shearer was developed and validated using the results of the experimental study. The CFD simulation results are in good agreement with the experimental results with a maximum of 9.7% variation. This validated CFD model can be used in future research to predict the effects of modifications to the scrubber system, including modifications to the scrubber inlet, to optimize the scrubber design, and to evaluate the effectiveness of adding a tailgate drum dust scrubber.

Crystallization is one of the most important separation and purification processes in chemical and especially in pharmaceutical industries. Currently most crystallization processes in the industry are based on batch crystallization; however, due to the variation of product quality per batch, efforts are made to move to continuous processes instead. In this respect, micro and meso scale reactors represents a promising technology due to enhanced heat and mass transfer rates, which, translated to particle generation, provide control of size, morphology, and composition. In this study, a meso-scale continuous crystallizer has been characterized and optimized. A stirred tubular continuous-crystallizer has been characterized and optimized in which the crystallization of active pharmaceutical ingredients (APIs) can be performed under controlled conditions. The crystallizer is formed by two tubes, one for nucleation and the other one for growth, in order to separate different phenomena to control better the process and hence the crystal size distribution. The optimized nucleation tube has a length of 35 cm and a diameter of 3 cm with a long axial blade across the tube with the length of 30 cm and 2.5 cm of diameter. The phenomena of mixing helps to achieve homogeneous supersaturation along the tube to prevent growth during the nucleation and enables narrow residence time distribution of the crystals in the tube with the help of gravity to achieve narrower crystal size distribution. Computational fluid dynamics (CFD) is used to optimize the process. CFD is the application of numerical methods to solve systems of partial differential equations related to fluid dynamics. The continuity and the momentum equations are the most commonly applied equations within CFD, and together they can be used to calculate the velocity and pressure distributions in a fluid.

The process used by the Norwegian company Hydro for making Vinyl Chloride Monomer (VCM) from natural gas and sodium chloride has been studied. A three dimensional CFD model representing the firebox of the EDC cracker has been developed using the commercial CFD tool Fluent. Heat to the cracker is delivered by means of combustion of a fuel gas consisting of methane and hydrogen. In the developed CFD model used in this work, the combustion reaction itself is omitted, and heat is delivered by hot flue gas. With the combustion reaction left out, the only means of tuning the CFD model is through the flue gas inlet temperature. With the flue gas inlet temperature near the adiabatic flame temperature, the general temperature level of the EDC cracker was reported to be too high. The outer surface temperature of the coil was reported to be 3-400 K higher than what was expected. By increasing the mass flow of flue gas and decreasing the temperature, the net delivered heat to the firebox was maintained at the same level as the first case, but the temperature on the coil was reduced by 100-150 K. Further reductions in the flue gas inlet temperature and modifications in the mass flow of flue gas at the different burner rows, eventually gave temperature distributions along the reaction coil, and flue gas and refractory temperatures, that resemble those in the actual cracker. The one-dimensional reactor model for the cracking reaction represents the actual cracker in a satsifactorily manner. The cracking reaction was simulated using a simple, global reaction mechanism, thus only the main components of the process fluid, EDC, VCM and HCl, can be studied. The model is written in a way suitable for implementation of more detailed chemical reaction mechanisms. The largest deviation in temperature between measured and simulated data are about 5%. At the outlet the temperature of the process fluid is equal to the measured data. The conversion of EDC out of the firebox is assumed to be 50 wt-%, this value is met exactly by the model.

Thesis (PhD) - Swinburne University of Technology, Faculty of Engineering and Industrial Sciences, 2008.
A thesis submitted for the degree of Doctor of Philosophy, Faculty of Engineering and Industrial Sciences, Swinburne University of Technology, 2008. Typescript. Bibliography: p. 129-142. Includes bibliographical references (p. 259-274)

In this thesis, store separation from two different configurations are solved using computational methods. Two different commercially available CFD codes
CFD-FASTRAN, an implicit Euler solver, and an unsteady panel method solver USAERO, coupled with integral boundary layer solution procedure are used for the present computations. The computational trajectory results are validated against the available experimental data of a generic wing-pylon-store configuration at Mach 0.95. Major trends of the separation are captured. Same configuration is used for the comparison of unsteady panel method with Euler solution at Mach 0.3 and 0.6. Major trends are similar to each other while some differences in lateral and longitudinal displacements are observed. Trajectories of a fueltank separated from an F-16 fighter aircraft wing and full aircraft configurations are found at Mach 0.3 using only the unsteady panel code. The results indicate that the effect of fuselage is to decrease the drag and to increase the side forces acting on the separating fueltank from the aircraft. It is also observed that the yawing and rolling directions of the separating fueltank are reversed when it is separated from the full aircraft configuration when compared to the separation from the wing alone configuration.

This thesis studies thermal comfort in heating, ventilation and air-conditioning (HVAC) scenarios with computational fluid dynamics (CFD) models at domain and occupant levels. Domain level comfort modelling, where the details of the occupant are not modelled, is investigated utilising Fanger’s Predicted Mean Vote (PMV) and Predicted Percentage of Dissatisfied (PPD) comfort models. Occupant level comfort modelling, where the occupant geometry and skin temperature are required, is explored using two different models. The first model termed the thermal manikin model couples the University of California Berkeley (UCB) psychological model to a new physiological model which neglects the thermal regulation of the human body, and consists of a central core at constant temperature surrounded by a layer with thickness and corresponding thermal properties to allow the skin temperature to vary over the modelled human body. The second model based on Gagge’s two-node model, which includes thermal regulation, yet assumes the skin temperature of the occupant to be spatially uniform. The models are validated with the experimental results from the Technical University of Denmark, which provides the data of the air flow, and the Indoor Environmental Quality (IEQ) laboratory at the University of Sydney, which offered the actual votes of human subjects for a range of environmental conditions. To conclude, the prediction of the skin temperature and its spatial variation is the most important parameter to predict occupant comfort correctly. The occupant level comfort modelling approach employing the thermal manikin is found to be the superior method to evaluate thermal comfort as it can still be accurate when the environment is complex. However, the computational cost and model setup time is high. Further work employing multi-node thermal manikin models would be a fruitful area of research if the accuracy of occupant comfort prediction in complex thermal environments is of interest.

Hydraulic energy absorbers may be described as high-loss centrifugal turbomachines arranged to operate as stalled torque converters. The device absorbs the kinetic energy of a vehicle in motion and dissipates the energy into water. A steady, single-phase, Computational Fluid Dynamics (CFD) simulation has been performed to investigate the flow field in a hydraulic energy absorber. It was determined that to better predict the performance of the energy absorber, more sophisticated modeling approaches may be needed. In this research, a steady, two-phase calculation with basic turbulence modeling was used as a first assessment. The two-phase model was used to investigate cavitation effects. Unsteady and advanced turbulence modeling techniques were then incorporated into single-phase calculations. The Multiple Reference Frame (MRF) Technique was used to model the interaction between the rotor and the stator. The calculations provided clearer details of the flow field without dramatically increasing the computational cost. It was found that unsteady modeling was necessary to correctly capture the close coupling between the rotor and the stator. The predicted torque in the unsteady calculations was 70% of the experimental value and twice of the result in the steady-state calculations. It was found that the inaccuracy of torque prediction was due to (1) high pressures in the regions with complicated geometrical boundaries and, (2) dynamic interactions between the rotor and the stator were not captured fully. It was also determined that the unrealistically low pressure values were not caused by the physical cavitation, but by the lack of proper boundary conditions for the model. Further integration of the modeling techniques studied would improve the CFD results for use in the design of the energy absorber.
Master of Science

This study uses CFD methodology to simulate an advanced Diesel engine operated at higher than conventional peak cylinder pressures. The existing mathematical models for Diesel combustion, pollutant formation and wall heat transfer are improved and validated for this operating range. The fluid flow is described via the gas-phase Favre-averaged transport equations, governing the conservation of mass, chemical species, momentum and energy, based on the Eulerian continuum framework. These equations are closed by means of the k — e turbulence model. The liquid phase uses the Lagrangian approach, in which parcels, representing a class of droplets, are described by differential equations for the conservation of mass, momentum and energy. The numerical solution of the gas phase is obtained by the finite volume method applied to unstructured meshes with moving boundaries. Diesel ignition is modeled via a reduced kinetics mechanism, coupled with a characteristic timescale combustion model. Additionally, NOx and soot emissions are simulated. For the elevated cylinder temperatures and pressures, the behaviour of the thermophysical properties of the gases and liquids involved is critically examined. A near-wall treatment is applied accounting for the large gradients of thermophysical properties in the vicinity of the wall. Furthermore an alternative combined combustion and emissions modelling approach, RIF, based on the laminar flamelet concept is tested. The methodology is validated by reference to experimental data from a research engine, a constant volume pressure chamber and a high-pressure DI Diesel engine at various operating conditions. The modified near-wall treatment gives better agreement with the heat transfer measurements. The methodology predicts Diesel combustion evolution reasonably well for the elevated pressures. Best agreement was achieved using the LATCT combustion model combined with a NOx and soot model. The predictions of emissions show encouraging trends especially regarding the soot/NOx tradeoff, but require tuning of model coefficients.

Thesis (PhD) - Swinburne University of Technology, School of Engineering and Science, 2009.
A thesis submitted in accordance with the regulations for the degree of Doctor of Philosophy, School of Engineering and Science, Swinburne University of Technology, 2009. Typescript. Includes bibliographical references (p. 315-330)

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.

In this study, commercially available Computational Fluid Dynamics (CFD) software, CFX-4.4 has been used for the simulations of aerosol transport through various aerosol-sampling devices. Aerosol transport was modeled as a classical dilute and dispersed two-phase flow problem. Eulerian-Lagrangian framework was adopted wherein the fluid was treated as the continuous phase and aerosol as the dispersed phase, with a one-way coupling between the phases. Initially, performance of the particle transport algorithm implemented in the code was validated against available experimental and numerical data in the literature. Code predictions were found to be in good agreement against experimental data and previous numerical predictions. As a next step, the code was used as a tool to optimize the performance of a virtual impactor prototype. Suggestions on critical geometrical details available in the literature, for a virtual impactor, were numerically investigated on the prototype and the optimum set of parameters was determined. Performance curves were generated for the optimized design at various operating conditions. A computational model of the Linear Slot Virtual Impactor (LSVI) fabricated based on the optimization study, was constructed using the worst-case values of the measured geometrical parameters, with offsets in the horizontal and vertical planes. Simulations were performed on this model for the LSVI operating conditions. Behavior of various sized particles inside the impactor was illustrated with the corresponding particle tracks. Fair agreement was obtained between code predictions and experimental results. Important information on the virtual impactor performance, not known earlier, or, not reported in the literature in the past, obtained from this study, is presented. In the final part of this study, simulations on aerosol deposition in turbulent pipe flow were performed. Code predictions were found to be completely uncorrelated to experimental data. The discrepancy was traced to the performance of the code's turbulent dispersion model. A detailed literature survey revealed the inherent technical deficiencies in the model, even for particle dispersion. Based on the results of this study, it was determined that while the code can be used for simulating aerosol transport under laminar flow conditions, it is not capable of simulating aerosol transport under turbulent flow conditions.

"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."

This thesis presents Computational Fluid Dynamics (CFD) simulations of renewable turbines akin to those used for wind, hydro, and tidal applications. The models developed took the form of actuator discs with the solution of incompressible Reynolds-Averaged Navier-Stokes equations with the k-ω SST turbulence models. Simulations were initially conducted of a single turbine in water and air and then two axially aligned turbines to study the flow field interactions. These models were compared with previous theoretical, experimental and numerical data evident in the literature. Generally, good agreement was found between these models and other analogous data sources in terms of velocity profiles in the far wake. The actuator disc method was underpinned using the transient actuator line method, which showed good agreement from a quantitative and qualitative viewpoint. However, it required significant additional computational time when compared to the actuator disc method. Each of the models were developed and solved using complimentary commercially available CFD codes, ANSYS-CFX and ANSYS-Fluent. For this type of study, a critical evaluation of these codes was in all probability performed for the first time, where it is shown that for the studies investigated in this thesis ANSYS-CFX performed better than ANSYS-Fluent with respect to the computational effort (i.e. time and lines of code).

A mathematical model for the determination of the aerodynamic forces acting on an aircraft is presented. The mathematical model is based on the generalization of the idea of aerodynamically steady motions. One important use of these results is the determination of steady (time-invariant) aerodynamic forces and moments. Such aerodynamic forces can be determined using computer simulation by determining numerically the associated steady flows around the aircraft when it is moving along such generalized steady trajectories. The method required the extension of standard (inertial) CFD formulations to general non-inertial reference frames. Generalized Navier-Stokes and Euler equations have been derived. The formulation is valid for all ranges of Mach numbers including transonic flow. The method was implemented numerically for the planar case using the generalized Euler equations. The developed computer codes can be used to obtain numerical flow solutions for airfoils moving in general steady motions (i.e. circular motions). From these numerical solutions it is possible to determine the variation of the lift, drag and pitching moment with respect to the pitch rate at different Mach numbers and angles of attack. One of the advantages of the mathematical model developed here is that the aerodynamic forces become well-defined functions of the motion variables (including angular rates). In particular, the stability derivatives are associated with partial derivatives of these functions. These stability derivatives can be computed using finite differences or the sensitivity equation method.
Ph. D.

Butterfly valves are commonly used in industrial applications to control the internal flow of both compressible and incompressible fluids. A butterfly valve typically consists of a metal disc formed around a central shaft, which acts as its axis of rotation. As the valve's opening angle is increased from 0 degrees (fully closed) to 90 degrees (fully open), fluid is able to more readily flow past the valve. Characterizing a valve's performance factors, such as pressure drop, hydrodynamic torque, flow coefficient, loss coefficient, and torque coefficient, is necessary for fluid system designers to account for system requirements to properly operate the valve and prevent permanent damage from occurring. This comparison study of a 48-inch butterfly valve's experimental performance factors using Computational Fluid Dynamics (CFD) in an incompressible fluid at Reynolds numbers ranging approximately between 105 to 106 found that for mid-open positions (30-60 degrees), CFD was able to appropriately predict common performance factors for butterfly valves. For lower valve angle cases (10-20 degrees), CFD simulations failed to predict those same values, while higher valve angles (70-90 degrees) gave mixed results. (152 pages)

With many decades of research devoted to the intriguing nature of vortex-induced vibrations, the offshore industry is constantly looking for new effective solutions in predicting VIV of slender marine structures such as riser pipes. These structures are very sensitive to excitations induced by vortex shedding, which results in vibrations that in certain combinations of waves and current develop into a structural resonance phenomenon known as lock-in. This kind of vibrations can be destructive to some structures and lead to collapse. Many of VIV aspects are far from being understood and advanced modelling is required to investigate the impact of the phenomenon, which significantly affects the service life of marine structures. The main objective of this research is to contribute to the family of semi-empirical models used for prediction of vortex-induced vibrations, with emphasis on low mass ratio elastically supported cylinders capable of moving in cross-flow and in-line directions. In this work a new two degree-of-freedom wake oscillator model has been developed, where vortex-induced lift and drag forces were modelled with two nonlinear self-excited oscillators of van der Pol type. Phenomena exclusive for two degreeof- freedom motion at low mass ratios were examined in detail. Computational fuid dynamics was applied to the problem in order to tune the model parameters. Twodimensional flow past an elastically supported cylinder was considered, and CFD simulation results were used to calibrate the wake oscillator model predictions of the complex fluid-structure interaction.

This thesis investigates the application of CFD techniques to the aerodynamic analysis of a U-shaped JETC. Investigations were carried out to determine the flow patterns present at a number of locations within the structure of a full U-shaped JETC. The CFD solutions produced in these investigations used recommendations from the literature in the set-up of the CFD solver, and provided the computational component towards problem-specific validation of the CFD techniques used. A structured series of CFD-aided investigation and design processes were then performed. These processes were based around a series of analyses that evaluated the influence of a number of cell parameters in terms of cell airflow efficiency and velocity distortion. Four cell components; the inlet and exhaust stack baffle arrangements, the turning-vanes, the rear of the working section and augmenter entrance, and the lower exhaust stack, including the BB, were investigated in individual analyses. Throughout the investigations the value of CFD as a design tool was constantly assessed. Overall, the findings suggest that aerodynamic optimisation of the baffle arrangements would provide the greatest gains to cell airflow efficiency. As some cells contain as many as three baffle arrangements, the potential increases made to cell airflow capacity are sizable. Through implementing the findings of the baffle arrangement investigations, static pressure loss across the five-row baseline arrangement was reduced by 79%. For low levels of velocity distortion in the upstream region of the working section, the need to design the inlet stack baffles in the turning-vane arrangement was highlighted. Mid-baffle vane alignment, consistent flow channels, and sufficiently low chord to gap ratios should be incorporated into a turning-vane design to maximise flow uniformity. The need for the baffle and vane components to combine with the geometry of the cell to limit adverse pressure gradients was found as a requirement to minimise inner corner separation, and the downstream threat it creates to a safe testing environment. CFD proved to be a valuable analysis tool throughout the investigations performed in this thesis. The number of design iterations analysed, and the detail of data that could be extracted, significantly exceeded what could have been achieved through an isolated experimental testing programme.

The quasi-steady state-space models generally used to simulate the dynamics of underwater vehicles perform well in most steady flow scenarios, and are therefore acceptable for modeling today\'s fleet of endurance-focused autonomous underwater vehicles (AUVs). However, with their usage of numerous assumptions and simplifications, these models are not well suited to certain unsteady flow situations and for use in the development of AUVs capable of performing more extreme maneuvers. In the interest of better serving efforts to design a new generation of more maneuverable AUVs, a tool for simulating vehicle maneuvering within computational fluid dynamics (CFD) based environments has been developed. Unsteady Reynolds-averaged Navier-Stokes (URANS) simulations are used in conjunction with a 6-degree-of-freedom (6-DoF) rigid-body kinematic model to provide a numerical test basin for vehicle maneuvering simulations. The accuracy of this approach is characterized through comparison with experimental measurements and quasi-steady state-space models. Three state-space models are considered: one model obtained from semi-empirical database regression (this is the method most commonly used in application) and two models populated with coefficients determined from the results of prescribed motion CFD simulations. CFD analyses focused on supporting the design of a general purpose AUV are also presented.
Ph. D.

Extensive research has been conducted in the area of journal bearings over many years for various operating conditions and geometry, effects of different types of lubricants (oil and water), different numbers (zero, one and three) and positions of grooves and the flow of lubricant between the shaft and bearing. One area of research has been developing methods to minimize the experimental time and cost of predicting the performance of journal bearings operating over a wide variety of conditions. This has led to numerical methods being developed and utilised for this purpose. Numerical methods are an important foundation for the development of Computational Fluid Dynamics (CFD). CFD method has proved to be a very useful tool in this research field. This project uses a CFD (specifically FLUENT) approach to simulate the fluid flow in a water lubricated journal bearing with equal spaced axial grooves. Water is fed into the bearing from one end. The lubricant is subjected to a velocity induced flow, as the shaft rotates and a pressure induced flow, as the water is pumped from one end of the bearing to the other. CFD software is used to simulate the fluid flow phenomenon that occurs during the process. Different parameters such as eccentricity ratio, number of grooves and groove orientation to the load line were examined. Lubricant pressure and velocity profiles were obtained and compared with available theoretical and experimental results. Two dimensional studies showed that the predicted maximum pressure and load carrying capacity from CFD were similar to the results from theoretical calculations. A small percentage difference (1.78% - 3.76%) between experimental and theoretical results was found. The pressure distribution in the lubricant shows that grooves decrease the pressure and load carrying capacity of the bearing. Swirl or turbulence does occur in the groove is affected by the viscosity of the lubricant. Three dimensional studies show that the pressure drops linearly from one end of the bearing to the other for no groove, concentric and three grooves cases. As the eccentricity increases, for one groove cases, the shape of the pressure profile changes to parabolic shape at positive region while the other pressure profiles drop linearly. The magnitude of the velocity it the bearing gap increased from 0.8 m/s to about 2.9 m/s when the shaft speed increased from zero to 5.5 m/s for a concentric and no groove case, similar changes were noted for all other cases. An interesting observation occurs when implementing the pressure profiles along the bearing. At cases such as zero and one groove condition and e = 0.4 and 0.6, lubricant flow back is observed at both inlet and outlet i.e. at certain area of the inlet, lubricant flowed out of the bearing against the supply pressure, a similar situation occurred at the exit of the bearing.

Extensive research has been conducted in the area of journal bearings over many years for various operating conditions and geometry, effects of different types of lubricants (oil and water), different numbers (zero, one and three) and positions of grooves and the flow of lubricant between the shaft and bearing. One area of research has been developing methods to minimize the experimental time and cost of predicting the performance of journal bearings operating over a wide variety of conditions. This has led to numerical methods being developed and utilised for this purpose. Numerical methods are an important foundation for the development of Computational Fluid Dynamics (CFD). CFD method has proved to be a very useful tool in this research field. This project uses a CFD (specifically FLUENT) approach to simulate the fluid flow in a water lubricated journal bearing with equal spaced axial grooves. Water is fed into the bearing from one end. The lubricant is subjected to a velocity induced flow, as the shaft rotates and a pressure induced flow, as the water is pumped from one end of the bearing to the other. CFD software is used to simulate the fluid flow phenomenon that occurs during the process. Different parameters such as eccentricity ratio, number of grooves and groove orientation to the load line were examined. Lubricant pressure and velocity profiles were obtained and compared with available theoretical and experimental results. Two dimensional studies showed that the predicted maximum pressure and load carrying capacity from CFD were similar to the results from theoretical calculations. A small percentage difference (1.78% - 3.76%) between experimental and theoretical results was found. The pressure distribution in the lubricant shows that grooves decrease the pressure and load carrying capacity of the bearing. Swirl or turbulence does occur in the groove is affected by the viscosity of the lubricant. Three dimensional studies show that the pressure drops linearly from one end of the bearing to the other for no groove, concentric and three grooves cases. As the eccentricity increases, for one groove cases, the shape of the pressure profile changes to parabolic shape at positive region while the other pressure profiles drop linearly. The magnitude of the velocity it the bearing gap increased from 0.8 m/s to about 2.9 m/s when the shaft speed increased from zero to 5.5 m/s for a concentric and no groove case, similar changes were noted for all other cases. An interesting observation occurs when implementing the pressure profiles along the bearing. At cases such as zero and one groove condition and e = 0.4 and 0.6, lubricant flow back is observed at both inlet and outlet i.e. at certain area of the inlet, lubricant flowed out of the bearing against the supply pressure, a similar situation occurred at the exit of the bearing.

Aerosolized medications can potentially be delivered to the lungs of infants through a nasal cannula interface. However, nose-to-lung delivery technologies currently allow for ~1% of the loaded dose to reach an infant’s lungs. Conventional dry powder inhalers (DPI) are superior to other types of inhalers in many ways. However, passive DPIs that operate based on user inhalation and require large volumes of airflow are not applicable to infants. To overcome this challenge, positive pressure DPIs have been developed that enable aerosol delivery to infants. Unless an adequate nasal interface is used with these devices, a significant amount of drug will still be lost. Computational fluid dynamics (CFD) provide a method to assess the performance of a nasal cannula interface and optimize its performance. In this study, a CFD model was first experimentally validated using the low-Reynolds number k-ω turbulence model, then used to assess and optimize several conical diffuser cannula designs for infants. The performance of a cannula depends primarily on two requirements: the amount deposited particles and the cannula’s volume. It was found that 90 and 100 mm long simple diffusers achieved the necessary deposition and volume requirements when operated at 3 and 5 liters per minute, respectively. Additionally, including clean sheath co-flow air with the 70 mm long diffuser achieved the targeted performance requirements. Inclusion of recent advancements in the field with the recommended cannula designs is likely to improve pharmaceutical aerosol delivery to infants using the nose-to-lung approach.

There is an ongoing interest in analyzing the flow characteristics of swimming fish. Biology has resulted in some very efficient motions and formulating these motions is of interest to engineers. One such theory was written by Dr. William Vorus and Dr. Brandon Taravella involving ideal efficiency. It is therefore interesting to test the calculations to see if it is possible to design a motion that can create thrust without necessarily creating vorticity. The computational fluid dynamics software of ANSYS Fluent was used to calculate the resulting flow field of the eel motion to compare with the theoretical values.

Understanding why fish move the way in which they do has applications far outside of biology. Biological propulsion has undergone millions of years of refinement, far outpacing the capabilities of anything created by man. Research in the areas of unsteady/biological propulsion has been increasing in the last several decades with advances in technology. Researchers are currently conducting experiments using pitching and heaving airfoils, mechanized fish, and numerical fish. However, the surrogate propulsors that are being used in experiments are driven analytically, whereas in this study, a method has been developed to exactly follow the motion of swimming fish. The research described in this thesis couples the image analysis of swimming fish with computational fluid dynamics to accurately simulate a virtual fish. Videos of two separate fish swimming modes were analyzed. The two swimming modes are termed `free-stream swimming' and the `Kármán gait'. Free-stream swimming is how fish swim in a section of water that is free of disturbances, while Kármán gait swimming is how fish swim in the presence of a vortex street. Each swimming mode was paired with two simulation configurations, one that is free of obstructions, and one that contains a vortex street generating D-section cylinder. Data about the efficiency of swimming, power output, and thrust production were calculated during the simulations. The results showed that the most efficient mode of swimming was the Kármán gait in the presence of a Kármán vortex street. Evidence corroborating this has been found in the literature. The second most efficient means of swimming was found to be free-stream swimming in the absence of obstructions. The other two configurations, which are not observed in experiments, performed very poorly in regard to swimming efficiency.

Computational Fluid Dynamics (CFD) is a field that is constantly advancing. Its advances in terms of capabilities are a result of new theories, faster computers, and new numerical methods. In this thesis, advances in the computational fluid dynamic modeling of moving bodies and combustive flows are investigated. Thus, the basic theory behind CFD is being extended to solve a new class of problems that are generally more complex. The first chapter that investigates some of the results, chapter IV, discusses a technique developed to model unsteady aerodynamics with moving boundaries such as flapping winged flight. This will include mesh deformation and fluid dynamics theory needed to solve such a complex system. Chapter V will examine the numerical modeling of a combustive flow. A three dimensional single vane burner combustion chamber is numerically modeled. Species balance equations along with rates of reactions are introduced when modeling combustive flows and these expressions are discussed. A reaction mechanism is validated for use with in situ reheat simulations. Chapter VI compares numerical results with a laminar methane flame experiment to further investigate the capabilities of CFD to simulate a combustive flow. A new method of examining a combustive flow is introduced by looking at the solutions ability to satisfy the second law of thermodynamics. All laminar flame simulations are found to be in violation of the entropy inequality.

This research concerns the development and validation of simulation of the beam-target interaction to determine the target temperature distribution as a function of time for a given target geometry, surface radiation intensity and free stream flow condition. The effect of a turbulent supersonic flow was investigated both numerically and experimentally. Experiments were in the Virginia Tech supersonic wind tunnel with a Mach 4 nozzle, ambient total temperature, total pressure of 160 psi and Reynolds number of 5 × 10⁷/m . The target consisted of a 6.35 mm stainless steel plate painted flat black. The target was irradiated with a 300 Watt continuous beam Ytterbium fiber laser generating a 4 mm Gaussian beam at 1.08 micron 10 cm from the leading edge where a 4 mm turbulent boundary layer prevailed. An absorbed laser power of 65, 81, 101, 120 Watts was used leading to a maximum heat flux between 1035 to 1910 W/cm². The target surface and backside temperature was measured using a mid-wave infrared camera. The backside temperature was also measured using eight type-K thermocouples. Two tests are made, one with the flow-on and the other with the flow-off. For the flow-on case, the laser is turned on after the tunnel starts and the flow reaches a steady state. For the flow-off case, the plate is heated at the same power but without the supersonic flow. The cooling effect is seen by subtracting the flow-off temperature from the flow-on temperature. This temperature subtraction is useful in cancelling the bias errors such that the overall uncertainty is significantly reduced. A new conjugate heat transfer algorithm was implemented in the GASP solver and validated by predicting the temperature distribution inside a cooled nozzle wall. The conjugate heat transfer algorithm was used to simulate the experiments at 81 and 65 Watts. Most computations were performed using the Spalart-Allmaras turbulence model on a 280, 320 cell grid. A grid convergence study was performed. At 65 Watts, good agreement was found in the predicted surface and backside temperature. On the surface, cooling was underpredicted close to the center and better agreement was seen away form the center. On the backside, good agreement was found for the temperature and temperature difference. Compared to the 65 Watt case, the 81 Watt case displays more asymmetry and a region of increased cooling is found upstream. The increased asymmetry was also seen on the backside by both the thermocouple and infrared temperature measurements. The computation underpredicts the surface temperature by 7% for the flow-off case. Again, cooling is underpredicted at the surface near the center. For all power settings, convective cooling significantly increases the time required to reach a given temperature.
Ph. D.

Impeller-stirred mixing is one of the most important processes employed throughout the chemical, metallurgical and allied industries. The research reported in this thesis is focused on impeller stirred mixing associated with the refining of lead bullion. The aim of this process is to sequentially remove contained impurities such as copper, antimony, silver and bismuth. This occurs in hemispherical vessels, called kettles, where reagents are initially added to the lead bath to form surface dross that contains both the required impurity and a large amount of lead oxide. This dross is then continuously mixed back into the bath to remove the lead oxide and capture more of the required impurity. A key requirement for this process is to obtain and remove dross that contains a high concentration of the impurity. Although this process has been in operation for many years, there is very little known on how the fluid dynamics associated with the mixing process affects final dross content. The aim of this research is to fully investigate the lead refining process using scientific analysis methods that help understand the mixing process and provide design tools which can be used to optimise process conditions. The three methods of analysis used are: (1) Direct readings from a real kettle, (2) Physical modelling (using water), and finally (3) Computational Fluid Dynamics (CFD). The use of physical modelling, exploiting the techniques of similitude, to predict vortex was also validated. An Acoustic Doppler Velocimeter (ADV) probe was used for the velocity measurement at various locations inside the water model and this gave valuable insight about the flow phenomena occurring inside the refining kettle. A particular important finding was that when fluid is stirred above certain rotational speed the vortex depth becomes independent of the Reynolds number of the operation. With regards CFD technology, the Volume of Fluid (VOF) method was used to capture the free surface and the Lagrangian Particle Tracking (LPT) and Algebraic Slip Model (ASM) to simulate the dross phase. Appropriate methods were also used to represent the moving impeller region. Validation of simulation results against experimental data was very encouraging. Computed vortex depth showed the similar trend as observed during the experiments on the physical model. A design strategy was developed that integrates results from both physical and computational modelling to allow optimal process conditions to be predicted at the kettle design stage. The use of this integrated physical and computational modelling methodology successfully helped eliminate surface swirl by introducing baffles to the kettle. The design and introduction of these flow controllers was also validated to ensure that it optimised the dross mixing process and final impurity content in the dross.

"This thesis presents a series of physical experiments and numerical simulations intended to determine whether the use of commercially available computational fluid dynamics (CFD) software may provide a viable alternative to the use of physical models for predicting the occurrence of vortices and swirl in pump intakes. The physical experiments were set up at Alden Research Laboratories, Inc. (ARL) of Holden, Massachusetts, using a simple pump intake model donated by ARL for use in this study. Swirl and velocity measurements and dye injections were used to characterize the flow in the physical model. Three flow conditions were chosen for the physical experiments because they demonstrated swirl and vortices developing at the pump intake. Once the physical experiments were performed, FIDAP, a general-purpose finite-element CFD package, was used to simulate the circulation patterns in the vicinity of a pump intake. The model configuration and scale were selected to simulate experimental conditions in the physical pump intake model. Some similarities were also identified in the locations of the models predicted vortex characteristics and the vortex characteristics that were observed in the experimental facility. However, the characteristics of swirl within the pump intake differed from experimental observations. Therefore, additional simulations were conducted to analyze the sensitivity of simulations to model assumptions. These additional simulations showed that the assumptions related to these model parameters have minor affects on the general nature of the predicted vortices, but do affect the predicted vortex strength. This thesis represents a first step in addressing the discrepancies between numerical and experimental results. Additional investigations are recommended to clarify the applicability of CFD to address pump intake problems."

The largest and most difficult numerical approximation error to estimate is discretization error. Residual-based discretization error estimation methods are a category of error estimators that use an estimate of the source of discretization error and information about the specific application to estimate the discretization error using only one grid level. The higher-order terms are truncated from the discretized equations and are the local source of discretization error. The accuracy of the resulting discretization error estimate depends solely on the accuracy of the estimated truncation error. Residual-based methods require only one grid level compared to the more commonly used Richardson extrapolation which requires at least two. Reducing the required number of grid levels reduces computational expense and, since only one grid level is required, can be applied to unstructured grids where multiple quality grid levels are difficult to produce. The two residual-based discretization error estimators of interest are defect correction and error transport equations. The focus of this work is the development, improvement, and evaluation of various truncation error estimation methods considering the accuracy of the truncation error estimate and the resulting discretization error estimates. The minimum requirements for accurate truncation error estimation is specified along with proper treatment for several boundary conditions. The methods are evaluated using various Euler and Navier-Stokes applications. The discretization error estimates are compared to Richardson extrapolation. The most accurate truncation error estimation method was found to be the k-exact method where the fine grid with a correction factor was considerably reliable. The single grid methods including the k-exact require that the continuous operator be modified at the boundary to be consistent with the implemented boundary conditions. Defect correction showed to be more accurate for areas of larger discretization error; however, the cost was substantial (although cheaper than the primal problem) compared to the cost of solving the ETEs which was essential free due to the linearization. Both methods showed significantly more accurate estimates compared to Richardson extrapolation especially for smooth problems. Reduced accuracy was apparent with the presence of stronger shocks and some possible modifications to adapt to singularies are proposed for future work.
Ph. D.

In this thesis work the feasibility of using open source OpenFOAM software as a solver part for Computation Fluid Dynamics in Volvo Technology is studied. Since the structure of the case in OpenFOAM is rather complex, one of the main purposes of this thesis work was also to make the process of using OpenFOAM as user-friendly as possible. The general conclusion that can be drawn from this work is that a very streamlined workflow can be, and has been, designed and created.

The main purpose of the dissertation is to contribute to the development of numerical techniques for computational heat transfer and fluid flow, suitable for low cost (loosely coupled) parallel computers. It is focused on implicit integration schemes, using finite control volumes with multigrid (MG) algorithms.

Natural convection in closed cavities is used as a problem model to introduce different aspects related with the integration of the incompressible Navier-Stokes equations, such as the solution of the pressure correction (or similar) equations that is the bottleneck of the algorithms for parallel computers. The main goal of the dissertation has been to develop new algorithms to advance in the solution of this problem rather than to implement a complete parallel CFD code.

An overview of different sequential multigrid algorithms is presented, pointing out the difference between geometric and algebraic multigrid. A detailed description of segregated ACM is given. The direct simulation of a turbulent natural convection flow is presented as an application example. A short description of the coupled ACM variant is given.

Background information of parallel computing technology is provided and the the key aspects for its efficient use in CFD are discussed. The limitations of low cost, loosely coupled cost parallel computers (high latency and low bandwidth) are introduced. An overview of different control-volume based PCFD and linear equation solvers is done. As an example, a code to solve reactive flows using Schwartz Alternating Method that runs particularly well on Beowulf clusters is given.

Different alternatives for latency-tolerant parallel multigrid are examined, mainly the DDV cycle proposed by Brandt and Diskin in a theoretical paper. One of its main features is that, supressing pre-smoothing, it allows to reduce the each-to-neighbours communications to one per MG iteration. In the dissertation, the cycle is extended to two-dimensional domain decompositions. The effect of each of its features is separately analyzed, concluding that the use of a direct solver for the coarsest level and the overlapping areas are important aspects. The conclusion is not so clear respect to the suppression of the pre-smoothing iterations.

A very efficient direct method to solve the coarser MG level is needed for efficient parallel MG. In this work, variant of the Schur complement algorithm, specific for relatively small, constant matrices has been developed. It is based on the implicit solution of the interfaces of the processors subdomains. In the implementation proposed in this work, a parallel evaluation and storage of the inverse of the interface matrix is used. The inner nodes of each domain are also solved with a direct algorithm. The resulting algorithm, after a pre-processing stage, allows a very efficient solution of pressure correction equations of incompressible flows in loosely coupled parallel computers.

Finally, all the elements presented in the work are combined in the DDACM algorithm, an algebraic MG equivalent to the DDV cycle, that is as a combination of a parallel ACM algorithm with BILU smoothing and a specific version of the Schur complement direct solver. It can be treated as a black-box linear solver and tailored to different parallel architectures.

The parallel algorithms analysed (different variants of V cycle and DDV) and developed in the work (a specific version of the Schur complement algorithm and the DDACM multigrid algorithm) are benchmarked using a cluster of 16 PCs with a switched 100 Mbits/s network.

The general conclusion is that the algorithms developed are suitable options to solve the pressure correction equation, that is the main bottleneck for the solution of implicit flows on loosely coupled parallel computers.

In this thesis a methodology is presented to optimise non–linear mathematical models in numerical engineering applications. The method is based on biological evolution and uses known concepts of genetic algorithms and evolutionary compu- tation. The working principle is explained in detail, the implementation is outlined and alternative approaches are mentioned. The optimisation is then tested on a series of benchmark cases to prove its validity. It is then applied to two different types of problems in computational engineering. The first application is the mathematical modeling of turbulence. An overview of existing turbulence models is followed by a series of tests of different models applied to various types of flows. In this thesis the optimisation method is used to find improved coefficient values for the k–ε, the k–ω-SST and the Spalart–Allmaras models. In a second application optimisation is used to improve the quality of a computational mesh automatically generated by a third party software tool. This generation can be controlled by a set of parameters, which are subject to the optimisation. The results obtained in this work show an improvement when compared to non–optimised results. While computationally expensive, the genetic optimisation method can still be used in engineering applications to tune predefined settings with the aim to produce results of higher quality. The implementation is modular and allows for further extensions and modifications for future applications.

At Amgen, the Automated Vision Inspection (AVI) systems capture the movement of unwanted particles in Amgen's drug product containers. For quality inspection, the AVI system must detect these undesired particles using a high speed spin-stop agitation process. To better understand the fluid movements to swirl the particles away from the walls, Computational Fluid Dynamics (CFD) is used to analyze the nature of the two phase flow of air and a liquid solution. Several 2-D and 3-D models were developed using Fluent to create simulations of Amgen's drug product containers for a 1 mL syringe, 2.25 mL syringe, and a 5 mL cartridge. Fluid motion and potential bubble formations were studied within the liquid/gas domain inside the container by varying parameters such as viscosity, angular velocity, and surface tension. Experiments were conducted using Amgen's own equipment to capture the images of the spin-stop process and validate the models created in Fluent. Observations were made to see the effects of bubble formation or splashing during spin-down to rest. The numerical and experimental results showed favorable comparison when measuring the meniscus height or the surface profile between the air and liquid. Also, at high angular velocity and dynamic viscosity, the container experiences instabilities and bubble formations. These studies indicate that CFD can be used as an useful and important tool to study fluid movement during agitation and observe any undesirable results for quality inspection.

Computational solutions are presented for flows ranging from incompressible viscous flows to inviscid transonic flows. The viscous flow problems are solved using the incompressible Navier-Stokes equations while the inviscid solutions are attained using the full potential equation. Results for the viscous flow problems focus on turbulence modeling when separation is present. The main focus for the inviscid results is the development of an unstructured solution algorithm. The subject dealing with turbulence modeling for separated flows is discussed first. Two different test cases are presented. The first flow is a low-speed converging-diverging duct with a rapid expansion, creating a large separated flow region. The second case is the flow around a stationary hydrofoil subject to small, oscillating hydrofoils. Both cases are computed first in a steady state environment, and then with unsteady flow conditions imposed. A special characteristic of the two problems being studied is the presence of strong adverse pressure gradients leading to flow detachment and separation. For the flows with separation, numerical solutions are obtained by solving the incompressible Navier-Stokes equations. These equations are solved in a time accurate manner using the method of artificial compressibility. The algorithm used is a finite volume, upwind differencing scheme based on flux-difference splitting of the convective terms. The Johnson and King turbulence model is employed for modeling the turbulent flow. Modifications to the Johnson and King turbulence model are also suggested. These changes to the model focus mainly on the normal stress production of energy and the strong adverse pressure gradient associated with separating flows. The performance of the Johnson and King model and its modifications, along with the Baldwin-Lomax model, are presented in the results. The modifications had an impact on moving the flow detachment location further downstream, and increased the sensitivity of the boundary layer profile to unsteady flow conditions. Following this discussion is the numerical solution of the full potential equation. The full potential equation assumes inviscid, irrotational flow and can be applied to problems where viscous effects are small compared to the inviscid flow field and weak normal shocks. The development of a code is presented which solves the full potential equation in a finite volume, cell centered formulation. The unique feature about this code is that solutions are attained on unstructured grids. Solutions are computed in either two or three dimensions. The grid has the flexibility of being made up of tetrahedra, hexahedra, or prisms. The flow regime spans from low subsonic speeds up to transonic flows. For transonic problems, the density is upwinded using a density biasing technique. If lift is being produced, the Kutta-Joukowski condition is enforced for circulation. An implicit algorithm is employed based upon the Generalized Minimum Residual method. To accelerate convergence, the Generalized Minimum Residual method is preconditioned. These and other problems associated with solving the full potential equation on an unstructured mesh are discussed. Results are presented for subsonic and transonic flows over bumps, airfoils, and wings to demonstrate the unstructured algorithm presented here.
Ph. D.

The research presented here provides a basis for understanding the hydrodynamics of surfboard fin geometries. While there have been select studies on fins there has been little correlation to the shape of the fin and its corresponding hydrodynamic performance. This research analyzes how changing the planform shape of a surfboard fin effects its performance and flow field. This was done by isolating the taper and sweep distribution of a baseline geometry and varying each parameter individually whilst maintaining a constant span and surface area. The baseline surfboard fin was used as a template in Matlab to generate a set of x and y coordinates that defined the outline of the fin shape. These coordinates were then altered by changing either the sweep or taper distribution and resulted in new, unique planform shapes. The new shapes were used to generate 3D models with the NACA 0006 foil as the cross-section hydrofoil. After the geometry was modeled, each fin was meshed and simulated in CFD for incidence angles ranging from 0o to 20o and a fin Reynolds Number of 3.51x105. When the sweep distribution was changed, there was a direct correlation to vortex formation off the leading edge. Increasing the sweep generated a stronger vortex that persisted for higher angles of attack and resulted in higher moments but increased drag. Changing the taper distribution was not as influential. The tapered fin set showed similar flow fields and body forces to each other. Making a fin more rectangular had slight decreases in drag but made the shape more prone to separation.

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.

This dissertation focuses on aerosol transport modeling in occupational environments and mining sites in Arizona using computational fluid dynamics (CFD). The impacts of human exposure in both environments are explored with the emphasis on turbulence, wind speed, wind direction and particle sizes. Final emissions simulations involved the digitalization process of available elevation contour plots of one of the mining sites to account for realistic topographical features. The digital elevation map (DEM) of one of the sites was imported to COMSOL MULTIPHYSICS® for subsequent turbulence and particle simulations. Simulation results that include realistic topography show considerable deviations of wind direction. Inter-element correlation results using metal and metalloid size resolved concentration data using a Micro-Orifice Uniform Deposit Impactor (MOUDI) under given wind speeds and directions provided guidance on groups of metals that coexist throughout mining activities. Groups between Fe-Mg, Cr-Fe, Al-Sc, Sc-Fe, and Mg-Al are strongly correlated for unrestricted wind directions and speeds, suggesting that the source may be of soil origin (e.g. ore and tailings); also, groups of elements where Cu is present, in the coarse fraction range, may come from mechanical action mining activities and saltation phenomenon. Besides, MOUDI data under low wind speeds (<2 m/s) and at night showed a strong correlation for particles 1-micrometer in diameter between the groups: Sc-Be-Mg, Cr-Al, Cu-Mn, Cd-Pb-Be, Cd-Cr, Cu-Pb, Pb-Cd, As-Cd-Pb. The As-Cd-Pb group correlates strongly in almost all ranges of particle sizes. When restricted low wind speeds were imposed more groups of elements are evident and this may be justified with the fact that at lower speeds particles are more likely to settle. When linking these results with CFD simulations and Pb-isotope results it is concluded that the source of elements found in association with Pb in the fine fraction come from the ore that is subsequently processed in the smelter site, whereas the source of elements associated to Pb in the coarse fraction is of different origin. CFD simulation results will not only provide realistic and quantifiable information in terms of potential deleterious effects, but also that the application of CFD represents an important contribution to actual dispersion modeling studies; therefore, Computational Fluid Dynamics can be used as a source apportionment tool to identify areas that have an effect over specific sampling points and susceptible regions under certain meteorological conditions, and these conclusions can be supported with inter-element correlation matrices and lead isotope analysis, especially since there is limited access to the mining sites. Additional results concluded that grid adaption is a powerful tool that allows to refine specific regions that require lots of detail and therefore better resolve flow detail, provides higher number of locations with monotonic convergence than the manual grids, and requires the least computational effort. CFD simulations were approached using the k-epsilon model, with the aid of computer aided engineering software: ANSYS® and COMSOL MULTIPHYSICS®. The success of aerosol transport simulations depends on a good simulation of the turbulent flow. A lot of attention was placed on investigating and choosing the best models in terms of convergence, independence and computational effort. This dissertation also includes preliminary studies of transient discrete phase, eulerian and species transport modeling, importance of saltation of particles, information on CFD methods, and strategies for future directions that should be taken.

This master thesis describes the co-firing concept, benefits and opportunities of pretreated biomass in pulverized coal boilers for industrial use. Burning fossil fuels, i.e. coal is under immense political pressure as European Union (EU) and other countries are trying to bring down the CO2 emission. Biomass combustion is already a proven technology and it plays a greater role in reducing CO2 emission. The main objective of this thesis is the brief study of computational fluid dynamics (CFD) modelling to examine the co-firing of greater amount of pretreated biomass and pulverized coal in a 200MWe pulverized coal boiler. Here, we exchange around 50 % of existing fuel in pulverized coal boiler with torrefied biomass. Torrefied biomass aids to increase the efficiency of existing coal boiler and cut down the CO2 emission. In this work, two cases of co-firing of pretreated biomass and coal have been investigated by CFD. Firstly, an experimental work was done in a laboratory scale to have few different types of torrefied biomass with different degrees of torrefaction. The devolatilization kinetics and char oxidation kinetics were also determined by experiments and other parameters have been calculated. One important aspect of this work has been to evaluate the performance of torrefaction based co-firing. Therefore, co-firing case has been compared to the 100 % coal feed case to understand the performance of torrefaction based co-firing. Furthermore, fluid flow, particles trajectories, heat transfer, and different emission behaviors have been studied. In addition, mechanisms of corrosion during co-firing have been studied and a guideline has been provided for corrosion model for analyzing the characteristics of alkali metals and their effects in co-firing coal boiler. The outcome from the CFD simulation indicated that boiler efficiency increases and the net CO2 emission reduced with increasing the biomass percentage in the co-firing system.

Through the last decades, building designers should deal with reliable design strategies to take advantage of natural resources in order to increase energy efficiency in buildings, as well as to promote sustainable development and add value to the society. This thesis proposes a reliable building design strategy to improve buildings energy efficiency by means of natural ventilation (NV) use. The strategy consists in evaluating the most suitable architectural solution in a particular case study taking into account environmental conditions and building surroundings in order to maximize NV use since the early building design stage. Computational fluid dynamics (CFD) techniques are used to conduct the research. This is a powerful design tool that permits buildings NV behaviour simulation prior to building construction. Therefore, the aim of the thesis is to provide a real case study building in which the NV design strategy is applied to show a reliable example and support building design decisions since the design stage. The design strategy is based on the use of a commercial numerical code that solves the fluid mechanic equations. The CFD software simulates the features that influence NV and predicts its behaviour in the different building configurations prior to building construction. This numerical technique allows, on the one hand, the visualization of air flow paths in buildings. On the other hand, many quantifiable parameters are calculated by the software. Through the analysis and comparison of those parameters, the best architectural solutions are chosen. With regards to all possible architectural decisions, the research is focused on the façade configuration selection and the building location. First of all, the NV design strategy feasibility is analysed in a particular region: the Mediterranean Valencian Coastal area (Spain). The region is characterized by the uniform conditions of the prevailing wind during the warm season. Then, a validated CFD simulation is used to analyse qualitatively and quantitatively the building surrounding influence on wind paths through and around buildings. The objective is to compare different façade opening positions and select the alternative that takes more profit of the NV resources available. Additionally, a general quantification of the ventilated façade contribution to buildings energy efficiency is presented under the frame of the façade configuration selection. Secondly, two simulations are conducted to analyse two different building locations. The assessment of surrounding buildings influence on building NV behaviour is done through validated CFD models. Some parameters and visualizations are proposed to be used in the quantitative and qualitative assessment of each solution respectively. Then, the best location alternative with regards to NV performance is selected. Finally, the research is concluded with the case study building full-scale construction. The indoor CFD simulation used from the beginning is then successfully validated. The NV building behaviour is also successfully verified. Additionally, contrasted performance indexes are used to evaluate indoor comfort conditions: draught risk (DR), predicted mean vote (PMV) and predicted percentage of dissatisfied people (PPD). The results show that comfort conditions can be reached more energy efficiently by means of NV use. Afterwards, it is verified how the comfortable indoor environment conditions are ensured and optimized by the NV use. Although the design strategy is applied to a particular building design, the design strategy potential is that it could be applied to all buildings. Consequently, major potential energy savings could be achieved.
Durante las últimas décadas los agentes involucrados en el diseño de edificios deben de utilizar estrategias fiables de diseño que les permitan aprovechar los recursos naturales del entorno con el objetivo de aumentar la eficiencia energética de los edificios así como promover el desarrollo sostenible y generar valor añadido para la sociedad. Esta tesis propone una estrategia de diseño fiable de edificios para mejorar su eficiencia energética mediante el uso de la ventilación natural (NV por sus siglas en inglés "natural ventilation"). La estrategia consiste en evaluar la solución arquitectónica más adecuada teniendo en cuenta las condiciones ambientales y el entorno de los edificios con el objetivo de maximizar el uso de la ventilación natural desde la fase inicial de su diseño. En esta tesis se aplica la estrategia de diseño a un caso de estudio real y particular. La estrategia de diseño se basa en el uso de un código numérico comercial que resuelve las ecuaciones de la mecánica de fluidos (CFD por sus siglas en inglés "computational fluid dynamics"). El software CFD simula las características que influyen en la ventilación natural y predice su comportamiento en los edificios antes de su construcción. Esta técnica numérica permite la visualización del flujo de aire en los edificios. Además, el software permite calcular parámetros que son analizados y comparados posteriormente para elegir la solución arquitectónica que suponga un mejor comportamiento de la ventilación natural. Con respecto a todas las decisiones arquitectónicas posibles, la investigación se centra en la selección de la ubicación del edificio y de la configuración de los huecos de su fachada. En primer lugar, se analiza la viabilidad de la estrategia de diseño en una región determinada: la zona costera Mediterránea de la Comunidad Valenciana. La región se caracteriza por las condiciones uniformes del viento predominante durante la estación cálida. A continuación, se utiliza una simulación de CFD validada para analizar cualitativamente y cuantitativamente la influencia de los edificios circundantes en los flujos del viento a través y alrededor de los edificios circundantes. El objetivo es comparar distintas posiciones de los huecos de la fachada para seleccionar la alternativa que mejor aproveche los recursos de ventilación natural disponibles. Además, se presenta en el marco de la selección de la configuración de la fachada una cuantificación general de la contribución de la fachada ventilada a la eficiencia energética de los edificios. En segundo lugar, se realizan dos simulaciones para analizar dos ubicaciones diferentes del edificio caso de estudio. La evaluación de la influencia de los edificios circundantes en el comportamiento de la ventilación natural del edificio caso de estudio se realiza mediante la utilización de modelos CFD validados. Se proponen distintos parámetros y visualizaciones para la evaluación cuantitativa y cualitativa de cada solución. A continuación se selecciona la mejor ubicación con respecto al comportamiento de la ventilación natural en el edificio caso de estudio. Finalmente, la investigación concluye con la construcción a escala real del edificio caso de estudio. Se valida con éxito la simulación CFD del interior del edificio utilizada desde la etapa de diseño. También se verifica con éxito el comportamiento de la ventilación natural del edificio. Además, se analizan las condiciones de confort interiores mediante la evaluación de los siguientes índices: riesgo de corrientes de aire (DR por sus siglas en inglés "draught risk"), voto promedio previsto (PMV por sus siglas en inglés "predicted mean vote") y el porcentaje previsto de personas insatisfechas (PPD por sus siglas en inglés "predicted percentage of dissatisfied people"). Los resultados muestran que el uso de la ventilación natural permite alcanzar, de manera más energéticamente eficiente, las
Durant les últimes dècades els agents involucrats en el disseny d'edificis utilitzen estratègies fiables de disseny que els permeten aprofitar els recursos naturals de l'entorn amb l'objectiu d'augmentar l'eficiència energètica dels edificis així com promoure el desenvolupament sostenible i generar valor afegit per la societat. Aquesta tesi proposa una estratègia fiable de disseny d'edificis per a millorar la seva eficiència energètica mitjançant l'ús de la ventilació natural (NV per les sigles en anglès "natural ventilation"). L'estratègia consisteix a avaluar la solució arquitectònica més adequada tenint en compte les condicions ambientals i l'entorn dels edificis amb l'objectiu de maximitzar l'ús de la ventilació natural des de la fase inicial del seu disseny. En aquesta tesi s'aplica l'estratègia de disseny a un cas d'estudi real i particular. L'estratègia de disseny es basa en l'ús d'un codi numèric comercial que resol les equacions de la mecànica de fluids (CFD per les sigles en anglès "computational fluid dynamics"). El programari CFD simula les característiques que influeixen en la ventilació natural i prediu el seu comportament en els edificis abans de la seva construcció. Aquesta tècnica numèrica permet la visualització del flux d'aire en els edificis. A més, el programari permet calcular paràmetres que són analitzats i comparats posteriorment per triar la solució arquitectònica que supose un millor comportament de la ventilació natural. Pel que fa a totes les decisions arquitectòniques possibles, la investigació es centra en la selecció de la ubicació de l'edifici i de la configuració de les obertures de la façana. En primer lloc, s'analitza la viabilitat de l'estratègia de disseny en una regió determinada: la zona costanera Mediterrània de la Comunitat Valenciana. La regió es caracteritza per les condicions uniformes del vent predominant durant l'estació càlida. A continuació, s'utilitza una simulació de CFD validada per analitzar qualitativament i quantitativament la influència dels edificis circumdants en els fluxos del vent a través i al voltant dels edificis circumdants. L'objectiu és comparar diferents posicions dels buits de la façana per seleccionar l'alternativa que millor aprofite els recursos de ventilació natural disponibles. A més, en el marc de la selecció de la configuració de la façana es presenta una quantificació general de la contribució de la façana ventilada a l'eficiència energètica dels edificis. En segon lloc, es realitzen dues simulacions per analitzar dues ubicacions diferents de l'edifici cas d'estudi. L'avaluació de la influència dels edificis circumdants en el comportament de la ventilació natural de l'edifici cas d'estudi es realitza mitjançant la utilització de models CFD validats. Es proposen diferents paràmetres i visualitzacions per a l'avaluació quantitativa i qualitativa de cada solució. A continuació es selecciona la millor ubicació pel que fa al comportament de la ventilació natural a l'edifici cas d'estudi. Finalment, la investigació conclou amb la construcció a escala real de l'edifici cas d'estudi. Es valida amb èxit la simulació CFD de l'interior de l'edifici utilitzada des de l'etapa de disseny. També es verifica amb èxit el comportament de la ventilació natural de l'edifici. A més, s'analitzen les condicions de confort interiors mitjançant l'avaluació dels següents índexs: risc de corrents d'aire (DR per les sigles en anglès "draught risk"), mitjana de vots previstos (PMV per les sigles en anglès "predicted mean vote") i el percentatge previst de persones insatisfetes (PPD per les sigles en anglès "predicted percentage of dissatisfied people"). Els resultats mostren que l'ús de la ventilació natural permet assolir, de manera més energèticament eficient, les condicions de confort.
Mora Pérez, M. (2017). Computational fluid dynamics (CFD) applied to buildings sustainable design: natural ventilation. Case study [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/86208
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