Truncation errors and computational cost are obstacles that still hinder large-scale applications of the Computational Fluid Dynamics method. The discontinuous Galerkin method is one of the high-order schemes utilized extensively in recent years, which is locally conservative, stable, and high-order accurate. Besides that, it can handle complex geometries and irregular meshes with hanging nodes. In this document, the nondimensional compressible Euler equations and Reynolds- Averaged Navier-Stokes equations are discretized by discontinuous Galerkin methods with a two-equations turbulence model on both structured and unstructured meshes. The traditional equation of state for an ideal gas model is substituted by a multispecies thermodynamics model in order to complete the governing equations. An approximate Riemann solver is used for computing the convective flux, and the diffusive flux is approximated with some internal penalty based schemes. The temporal discretization of the partial differential equations is either performed explicitly with the aid of Rung-Kutta methods or with semi-implicit methods. Inspired by the artificial viscosity diffusion based limiter for shock-capturing method, which has been extensively studied, a novel and robust technique based on the introduction of mass diffusion to the species governing equations to guarantee that the species mass fractions remain positive has been thoroughly investigated. This contact-surface-capturing method is conservative and a high order of accuracy can be maintained for the discontinuous Galerkin method. For each time step of the algorithm, any trouble cell is first caught by the contact-surface discontinuity detector. Then some amount of mass diffusions are added to the governing equations to change the gas mixtures and arrive at an equilibrium point satisfying some conditions. The species properties are reasonable without any oscillations. Computations are performed for many steady and unsteady flow problems. For general non-mixing fluid flows, the classical air-helium shock bubble interaction problem is the central test case for the high-order discontinuous Galerkin method with a mass diffusion based limiter chosen. The computed results are compared with experimental, exact, and empirical data to validate the fluid dynamic solver.

The FanWing propulsion system is a novel propulsion system which aerodynamically behaves as a hybrid between a helicopter and a fixed wing aircraft, and if the knowledge base with regards to this novel concept can be fully explored, there could be a new class of aircraft developed. In the current research, only 2D CFD studies have been done for the FanWing, hence the 3D lift characteristics of the FanWing have been unknown thus far, at least in the theoretical domain. Therefore, it was proposed to develop a modified Prandtl's Lifting Line Theory numerical solution and a CFD solution, comparing the results of each. A new variable was introduced into the classical Lifting Line Theory solution, αi,FW, to account for the additional lift produced by the FanWing as opposed to a traditional airfoil. This variable, αi,FW, is a function of the wing angle and the velocities taken at three-quarter chord length on the FanWing. The introduction of this variable was informed by other papers which superimposed velocities when developing Lifting Line Theory for unconventional airfoil planforms. After introducing a correction factor, the numerical model aligned with the 3D CFD results where LLT assumptions were valid. For the 3D simulation, it was observed that the lift per unit span rapidly increases from quarter span to wingtip, which is different from traditional wing planforms. This study provides a valuable first step towards documenting the 3D lift characteristics of the novel FanWing propulsion system.

<p>A study has been undertaken to investigate the flow structure in the vicinity of discontinuities in the surface of a high-speed air vehicle. The effect of gaps and steps on aerodynamic heating is of particular interest. The present    thesis presents Reynolds-averaged Navier Stokes  (RANS) calculations of this class of flow. This thesis consists of two studies: a parametric study of cavity flow at Mach 2 and a study to compare with wind tunnel experiments at Mach 6. The calculations for the parametric study used the Menter two-equation SST turbulence model at fully turbulent conditions. These are two-dimensional cavity flows that were carried out to identify the influence of cavity geometry on flow structure and heating distribution inside the cavity, and to categorize cavity flow regimes. The second study employed RANS calculations for conditions  corresponding to Mach 10 wind tunnel experiments carried out by Nestler et al. (AIAA Paper 1968-673) for Mach 6 boundary layer edge conditions. The SST model used in the parametric study was paired with the Menter oneequation transition model and the two-equation realizable κ-ϵ model in CFD++ was used for the computations. The results showed that, even with adjustment of model parameters, the Menter transition model cannot match the location of laminar to turbulent transition, but it demonstrated good agreement with the experimental data in fully turbulent conditions. The two-equation realizable κ-ϵ model, available in CFD++, was able to accurately model transition and showed favorable agreement for fully turbulent conditions as well.</p>

Detta är en rapport som beskriver utvecklingen av ett produktkoncept som är tänkt att ersätta Weda:s SD-enhet. SD-enheten är ett munstycke som kan tillverkas från 1𝑚 upp till 10𝑚 brett i bockad plåt och sitter installerad på en drivenhet. Denna ersättare av SD-enheten ska göras mer anpassningsbar efter olika bassängstorlekar och billigare i tillverkningskostnader. Baserat på kundkrav, problemställning och till följd av en utvecklingsprocess togs det fram fem koncept där samtliga stöds av grundläggande fakta, teoretiska tillverknings och monterings aspekter samt flödessimuleringar. Dessa fem koncept sattes emot varandra i en sållnings matris för att sedan gå vidare med ett koncept som vidareutvecklades med hjälp av projektverktyg som QFD och DFA. Slutligen utfördes en laboration med en prototyp med syfte att undersöka och stärka projektets beräkningar. Avslutningsvis analyseras resultaten som ställts upp mot projektets mål och kundkrav för att värdera om projektet har lyckats eller ej. / This report describes the development of a product concept that’s supposed to replace Weda's SD-System. The SD-System suction nozzle is scalable from 1 𝑚 up to 10 𝑚 wide out of bent sheet metal and is installed to a driving unit. The new pool cleaner attachment concept is supposed to be more modular to fit different basins and be cheaper in manufacturing. Based on customer requirements, the problems description and the development process, five concepts were developed. All the concepts are supported by basic facts, theoretical manufacturing and assembly aspects as well as flow simulations. These five concepts were opposed to each other in a screening matrix and then proceeded with a concept that was further developed using project tools such as QFD and DFA. Finally, a laboratory exercise was performed with a prototype and the purpose of investigating and strengthening the project's calculations. Finally, the results that are set against the project's objectives and customer requirements are analyzed to evaluate whether the project has succeeded or not.

With this contribution to the AVT-113/VFE-2 task group it was possible to prove the feasibility of high Reynolds number CFD computations to resolve and thus better understand the peculiar dual vortex system encountered on the VFE-2 blunt leading edge delta wing. Initial investigations into this phenomenon seemed to undermine the hypothesis, that the formation of the inner vortex system relies on the laminar state of the boundary layer at separation onset. As a result of this research, this initial hypothesis had to be expanded to account also for high Reynolds number cases, where a laminar boundary layer status at separation onset could be excluded. Furthermore, the data published in the same context shows evidence of secondary separation under the inner primary vortex. This further supports the supposition of a different generation mechanism of the inner vortical system other than a pure development out of a possibly laminar separation bubble. The unsteady computations performed on numerical grids with different levels of refinement led furthermore to the establishment of internal guidelines specific to the DES approach. / QC 20101111

Producing gasoline-type fuels from lignocellulosic biomass has two advantages over producing alcohol-type fuels from plant sugars: gasoline has superior fuel characteristics and plant lignin/cellulose does not compete with human food supplies. A promising technology for converting lignocellulose to fuel is catalytic fast pyrolysis (CFP). The process involves injecting finely ground biomass into a fluidized bed reactor (FBR) at high temperatures, which reduce the biomass to gases that react inside the catalyst particles. This entails complex hydrodynamics to efficiently mix a stream of biomass into a catalyst bed that is fluidized by a separate stream of inert gas. Understanding the hydrodynamics is complicated by the fact that the entire process occurs inside a heavily insulated, opaque, reactor vessel. Numerical simulations offer a promising approach to understanding, predicting, and optimizing hydrodynamic mixing in a CFP biomass reactor. The purpose of this research is to understand the simulation techniques and statistical measures appropriate for quantifying mixing in a CFP biomass reactor. The methodology is validated against the canonical configuration of a non-reacting, single-inlet fluidized bed. A new finding is that the minimum bubbling velocity may be predicted by a significant increase in temporal variance of the pressure drop. The methodology is then applied to a non-canonical FBR in which biomass is injected into the catalyst bed via a vertical center tube. Since no hydrodynamic mixing data exist from laboratory experiments, mixing is inferred from the aromatics yield from the laboratory reactor. Flow configurations with which simulations demonstrate the best mixing have the highest aromatic yields in the experiments. The simulations indicate that when the bed is in the bubbling regime, the gasified biomass from the center tube is efficiently mixed radially throughout the catalyst bed. If the flow rate of inert gas is insufficient to bubble the bed, then the gasified biomass exits the center tube, reverses direction, and flows upward along the tube's outside wall. Provided the bed is bubbling due to the inert gas stream, the upper limit on the flow through the center tube, and thus the aromatic yield potential, has yet to be determined.

With the global deployment of renewable energy generation at record rates, clean energy is steadily becoming competitive with its fossil-fuel counterparts. However, further expansion is limited by the inherent intermittency of renewable energy sources (solar, wind, wave, etc.), which typically do not match with daily and seasonal variations of global (and local) energy demand. Thermochemical energy storage (TCES) has demonstrated strong potential in being a technological pathway to provide on-demand process heat and handle the intrinsic variations in renewable energy generation and energy demand. TCES works on the premise of excess renewable heat driving an endothermic reduction reaction, in which thermal energy is converted to chemical potential energy. The reversed exothermic oxidation reaction is subsequently triggered (on-demand) to recover thermal energy which can be used as process heat. While the benefits of TCES have been demonstrated experimentally at the lab-scale, accurate numerical modeling of TCES reactors is key for future development, optimization, and implementation of large industrial-scale energy storage systems. This dissertation focuses on the development of continuum-scale models to accurately simulate and predict performance of high temperature (up to 1500 °C) moving-bed reactors for TCES. The efficacy of present volume- averaging approaches is briefly reviewed, with the major focus of the work on the development of multi-dimensional multi-physics models of increasing complexity for moving-bed TCES reduction and oxidation reactors.

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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. / Dissertation (MEng)--University of Pretoria, 2020. / Advanced Metals Initiative Suid Afrikaanse Akademie vir Wetenskap en Kuns / Chemical Engineering / MEng / Unrestricted

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