This thesis presents a computational fluid dynamic (CFD) study of high pressure gas turbine blade design with different realistic inlet temperature and velocity boundary conditions. The effects of blade shaping and inlet conditions can only be fully understood by considering the aerodynamics and heat transfer concurrently; this is in contrast to the sequential method of blade design for aerodynamics followed by cooling. The inlet boundary conditions to the NGV simulations are governed by the existence of discrete fuel injectors in the combustion chamber. An appreciation of NGV shaping design under engine realistic inflow conditions will allow for an identification of the correct three dimensional shaping parameters that should be considered for design optimisation. The Rolls-Royce efficient Navier-Stokes solver, HYDRA, was employed in all computational results for a transonic turbine stage. The single passage unsteady method based on the Fourier Shape Correction is adopted. The solver is validated under both rich burn (hot steak only) and the case with swirl inlet profiles for aerothermal characteristics; good agreement is noted with the validation data. Post processing methods were used in order to obtain time-averaged results and blade visualisations. Subsequently, a surrogate design optimisation methodology using machine learning combined with a Genetic Algorithm is implemented and validated. A study of the effect of NGV compound lean on stage performance is carried out and contrasted for uniform and rich burn inlets, and subsequently for lean burn. Compound lean is shown to produce a tip uploading at the rotor inlet, which is beneficial for rich burn, but detrimental for lean burn. It is also found that for rich burn, fluid driving temperature is more dominant than HTC in determining rotor blade heat transfer, the opposite sense to the uniform inlet. Also, for a lean burn inlet, there is another role reversal, with HTC dominating fluid driving temperature in determining heat transfer. A novel NGV design methodology is proposed that seeks to mitigate the combined effects of inlet hot streak and swirling flow. In essence, the concept two NGVs in a pair are shaped independently of each other, thus allowing the inlet flow non uniformity to be suitably accommodated. Finally, two numerical NGV optimisation studies are undertaken for the combined hot streak and swirl inlet for two clocking positions; vane impinging and passage aligned. Due to the prohibitive cost of unsteady CFD simulations for an optimisation strategy, a suitable objective function at the NGV exit plane is used to minimise rotor tip heat flux. The optimised shape for the passage case resulted in the lowest tip heat flux distribution, however the optimum shape for the impinging case led to the highest gain in stage efficiency. This therefore suggests that NGV lean and clocking position should be a consideration for future optimisation and design of the HP stage.

[pt] O presente trabalho é um estudo experimental das características de troca de calor e massa de um jato de ar incidindo ortogonalmente sobre uma placa. o estudo tem por objetivo avaliar a influência nos coeficientes de troca da presença de um componente circunferencial na velocidade do jato. Durante os experimentos foram investigadas a influência do número de Reynolds do jato, da distância jato/placa e da intensidade do escoamento espiralado (número de swirl). Os coeficientes de troca foram determinados utilizando-se a técnica de sublimação de naftaleno em conjunto com a analogia entre os provessos de transferência de calor e massa. Coeficientes de troca de massa locais foram determinados utilizando-se uma mesa de coordenadas computadorizada especialmente construída, que permitiu a obtenção de medidas detalhadas tanto na região de estagnação do jato quanto na região mais externa. Coeficientes globais de troca de massa foram obtidos independentemente dos locais através de pesagem. Os resultados demonstraram uma diminuição nos coeficientes de troca de massa do jato com o aumento da intensidade do escoamento espiralado. Visualizações do escoamento junto à placa foram realizadas, utilizando-se a técnica de óleo com o negro de fumo. Os resultados das visualizações demonstraram a existência de regiões de separação junto à fronteira da zona de estagnação. Para altos valores do número de swirl foram verificadas fortes reversões do escoamento na região de estagnação. / [en] The present work is an experimental study of the mass transfer characteristics of a swirling jet impinging on a flat plate. The main objective of the investigation was to determine the influence of a circumferential velocity component (the swirl component) on the local and average mass transfer coefficients at the plate surface. The dimensionless parameters investigated were the jet Reynolds number, the jet-to-plate distance, and the strength of the swirl flow given by the swirl number. Mass transfer coefficients were obtained utilizing the naphthalene sublimation technique. The local coefficients were determined employing a computerized coodinate table which allowed a detailed study of the effects of the presence of the swirl component. Average coefficients were determined independently through precision weighing, and displayed excellent agreement with the integrated local coefficients. The results demonstrated that the presence of the swirl component decreases the mass transfer coefficients, when compared with the non-swirl case. Flow visualization experiments were conducted utilizing the oil-lamp black technique. The results revealed regions of reverse flow at the stagnation zone for high values of the swirl number.

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The late University of Canterbury civil engineering lecturer Peter Giddens developed a range of simple microhydro turbines, with publications from as early as the 1980s. He considered that a range of simple but well-designed turbines which covered the gamut of possible small sites would be more useful than any single turbine. He started with radial inflow turbines, then set about extending their range of applicability by increasing specific speed. That extension was continued by the research in this thesis, which aimed to produce a design with a minimum efficiency of 70 % at a specific speed of at least 600 (rev/min, kW, m). Achieving those targets would differentiate it from existing microhydro designs. In order to reach those performance targets, the volute, runner, and draft tube were examined through experiment and computational fluid dynamics models to characterize past designs and test the validity of their embodied assumptions. A prototype with a design specific speed of 650 was built and fully characterized by dynamometer testing. Measurements of the outlet velocity distribution of two of Peter Giddens’s volutes confirmed that single tangential inlet volutes are not torque-free when certain geometric conditions are met; swirl increased through those volutes by 70 % or more depending on the design. A new overall turbine design was proposed, where axial flow enters the runner and swirling flows leaves it. This required the design of a novel volute. Through computational analysis, the effect of swirling flow entering the conical draft tube was shown to affect its pressure recovery: negatively for draft tubes with small angles, positively for larger angles. It was shown that the peak pressure recovery of an optimum draft tube was not likely to be improved upon by the use of swirl, and since there was uncertainty in the analysis, a conservative draft tube was specified for the prototype. A flat-bladed runner was designed for the prototype and computational modeling indicated its performance would be sensitive to small changes in flow angle. Despite that sensitivity — an intrinsic property of high specific speed runner velocity triangles — the computational model was shown to give good predictions of the runner flow characteristics, although not its effciency. Finally, a 1.2 kW prototype was built and achieved a peak net effciency of 64 % as defined by the American Society of Mechanical Engineers at a net head of 2.07 m, a flowrate of 94 L/s, and a runner shaft speed of 1670 rev/min, corresponding to a specific speed of 740. Maximum measured runner efficiency of 87 % also occurred at those conditions. Compared to existing designs, that performance extended the operational envelope of microhydro turbines considerably. A three-zone computational model of the entire prototype was assembled and trialled, but not validated. It is concluded that for efficient high specific speed turbines, volute swirl characteristics must be known with confidence, as the volute sets the conditions at the leading edge for peak runner efficiency. A simple but efficient runner may be made using flat blades, showing the potential for this geometry even when made by limited workshops. Adding a free-vortex tangential velocity distribution to the inlet flow of a stalled conical draft tube may increase its pressure recovery, although it is not likely to exceed the best performance obtainable with axial inlet flow. Therefore taking measures to reduce the peak fluid velocity entering the draft tube could be more beneficial to overall performance than seeking outright improvements in draft tube pressure recovery.

The use of a swirling flow can provide a more uniform velocity distribution and a calmer filling condition according to previous studies of both ingot and continuous casting processes of steel. However, the existing swirling flow generation methods developed in last decades all have some limitations. Recently, a new swirling flow generator, the TurboSwirl device, was proposed. In this work, the convergent nozzle was studied with different angles. The maximum wall shear stress can be reduced by changing the convergent angle between 40º and 60º to obtain a higher swirl intensity. Also, a lower maximum axial velocity can be obtained with a smaller convergent angle. Furthermore, the maximum axial velocity and wall shear stress can also be affected by moving the location of the vertical runner. A water model experiment was carried out to verify the simulation results of the effect of the convergent angle on the swirling flow pattern. The shape of the air-core vortex in the water model experiment could only be accurately simulated by using the Reynolds Stress Model (RSM). The simulation results were also validated by the measured radial velocity in the vertical runner by the ultrasonic velocity profiler (UVP). The TurboSwirl was reversed and connected to a traditional SEN to generate the swirling flow. The periodic characteristic of the swirling flow and asymmetry flow pattern were observed in both the simulated and measured results. The detached eddy simulation (DES) turbulence model was used to catch the time-dependent flow pattern and the predicted results agree well with measured axial and tangential velocities. This new design of the SEN with the reverse TurboSwirl could provide an almost equivalent strength of the swirling flow generated by an electromagnetic swirling flow generator. It can also reduce the downward axial velocities in the center of the SEN outlet and obtain a calmer meniscus and internal flow in the mold. / Tidigare studier visar att ett roterande flöde kan ge en mer likformig hastighetsfördelning och en lugnare fyllning i både göt- och stränggjutning av stål. De befintliga metoderna för att generera ett roterande flöde har vissa begränsningar. En ny metod för att generera det roterande flödet, en så kallad TurboSwirl, föreslogs nyligen. I detta arbete undersöktes ett konvergent munstycke med olika vinklar för att se hur detta påverkade det roterande flödet som genererades i anordningen. Resultaten visar att skjuvspänningen i systemet kan reduceras genom att ändra munstyckets vinkel mellan 40º till 60º. En lägre maximal axiell hastighet kan också uppnås med en mindre konvergent vinkel på munstycket. Det är även möjligt att påverka den maximala axiella hastigheten och skjuvspänningen i systemet genom att förflytta den vertikala kanalen i anordningen. Vattenmodellexperiment har utförts för att validera simuleringsresultaten. Det kraftigt roterande flödet kunde endast beskrivas väl av Reynolds Stress Model (RSM). Validering utfördes också genom att mäta den radiella hastigheten i den vertikala kanalen med en Ultrasonic Velocity Profiler (UVP). TurboSwirl-anordningen vändes och kopplades till gjutröret för att generera det roterande flödet. Detta studerades både med numeriska modeller och med vattenmodellering. Ett periodiskt asymmetriskt roterande flöde observerades både i numeriska modellerna och i vattenmodellerna. För att modellera detta periodiska flöde så användes detached eddy simulation (DES) modellen. Resultaten då denna modell användes stämmer väl med de experimentella mätningarna. Denna nya design med TurboSwirl kan uppnå liknande styrka på det roterande flödet som när elektromagnetisk omrörning användes. Det resulterande roterande flödet leder till en lägre axiell hastighet i gjutröret samt en lugnare yta och ett lugnare flöde i kokillen. / <p>QC 20161123</p>

<p>Despite its importance in various industrial applications there is still a lack of experimental studies on the dynamic and thermal field of swirling jets in the near-field region. The present study is an attempt to close this lack and provide new insights on the effect of rotation on the turbulent mixing of a <i>passive scalar</i>, on turbulence (joint) statistics as well as the turbulence structure.</p><p>Swirl is known to increase the spreading of free turbulent jets and hence to entrain more ambient fluid. Contrary to previous experiments, which leave traces of the swirl generating method especially in the near-field, the swirl was imparted by discharging a slightly heated air flow from an axially rotating and thermally insulated pipe (6 m long, diameter 60 mm). This gives well-defined axisymmetric streamwise and azimuthal velocity distributions as well as a well-defined temperature profile at the jet outlet. The experiments were performed at a <i>Reynolds</i> number of 24000 and a swirl number (ratio between the angular velocity of the pipe wall and the bulk velocity in the pipe) of 0.5.</p><p>By means of a specially designed combined X-wire and cold-wire probe it was possible to simultaneously acquire the instantaneous axial and azimuthal velocity components as well as the temperature and compensate the former against temperature variations. The comparison of the swirling and non-swirling cases clearly indicates a modification of the turbulence structure to that effect that the swirling jet spreads and mixes faster than its non-swirling counterpart. It is also shown that the streamwise velocity and temperature fluctuations are highly correlated and that the addition of swirl drastically increases the streamwise<i> passive scalar</i> flux in the near field.</p>