Modeling of complex flows involving the combined effects of flow transition and streamline curvature using two advanced turbulence models, one in the Reynolds-averaged Navier-Stokes (RANS) category and the other in the hybrid RANS-Large eddy simulation (LES) category is considered in this research effort. In the first part of the research, a new scalar eddy-viscosity model (EVM) is proposed, designed to exhibit physically correct responses to flow transition, streamline curvature, and system rotation effects. The four equation model developed herein is a curvature-sensitized version of a commercially available three-equation transition-sensitive model. The physical effects of rotation and curvature (RC) enter the model through the added transport equation, analogous to a transverse turbulent velocity scale. The eddy-viscosity has been redefined such that the proposed model is constrained to reduce to the original transition-sensitive model definition in nonrotating flows or in regions with negligible RC effects. In the second part of the research, the developed four-equation model is combined with a LES technique using a new hybrid modeling framework, dynamic hybrid RANS-LES. The new framework is highly generalized, allowing coupling of any desired LES model with any given RANS model and addresses several deficiencies inherent in most current hybrid models. In the present research effort, the DHRL model comprises of the proposed four-equation model for RANS component and the MILES scheme for LES component. Both the models were implemented into a commercial computational fluid dynamics (CFD) solver and tested on a number of engineering and generic flow problems. Results from both the RANS and hybrid models show successful resolution of the combined effects of transition and curvature with reasonable engineering accuracy, and for only a small increase in computational cost. In addition, results from the hybrid model indicate significant levels of turbulent fluctuations in the flowfield, improved accuracy compared to RANS models predictions, and are obtained at a significant reduction of computational cost compared to full LES models. The results suggest that the advanced turbulence modeling techniques presented in this research effort have potential as practical tools for solving low/high Re flows over blunt/curved bodies for the prediction of transition and RC effects.

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The passage of No Child Left Behind has increased the level of accountability for all educators. There are many factors that affect student achievement. One factor that may be overlooked is the schedule configuration of schools. Addressing student needs through scheduling options may assist school systems and students in performing at the level they are being held accountable. The population for this study was students from a rural East Tennessee middle school with a population of approximately 700 students. The low socioeconomic students represent 68% of the school total enrollment while 18% of the students have an individual education plan (IEP). The gender of the school is nearly 50% male and female. Looking at 2 research questions, an independent t test was used to determine if there was a significant difference in reading-language arts and mathematics Tennessee Comprehensive Assessment Program (TCAP) scores after implementing a rotating schedule. Subgroups used in this study were: students with an Individual Education Plan (IEP), low socioeconomic students, male and female students. Results of this study were mixed. Students with an IEP showed an increase in both reading-language arts and mathematics. For all subgroups in reading, there was an increase in achievement although the results showed that there was not a significant relationship between the rotating schedule and student achievement. The only group to show gains in mathematics after implementation of the rotating was those students with an IEP. Each of the 3 remaining subgroups actually showed a loss and there was a significant relationship between the rotating schedule and student achievement.

Additive manufacturing (AM), also known as 3D-printing is an automated manufacturing process in which the component is built layer upon layer from a predefined 3D computer model. In contrast to conventional manufacturing processes where a vast volume of material is wasted due to machining, AM only uses the material that the component consists of. In addition to material savings, the method has a number of potential benefits. Two of these are (1) a large design freedom which enables the production of complex geometries and (2) a reduced compexity in supply chain as parts can be printed on-demand rather than be kept in stock. This master thesis has been performed at Vattenfall Wind Power and aims to investigate the feasibility to reproduce and/or to refurbish one or two spare parts on a wind turbine by AM and if it can introduce any practical benefits. Components with a high failure rate and/or with an suitible design for AM have been investigated. A rotating union or fluid rotary joint (FRJ) was selected for further analysis. A comprehensive background study has been conducted. A current status of metal AM is described as well as a comparison between conventional and additive processes. Furthermore, current and future applications for AM witihin the wind turbine industry are presented. The mehodology "reverse engineering", main components in a wind power plant including the fluid rotary joint as well as fluid dynamics are also treated in the background study. As a part of the process, a fluid rotary joint with worse historical failure data was disassembled and examined. In order to find other design solutions that contributes to a better and more reliable operation, another better performing fluid roraty joint was investigated. Since detail drawings and material information are missing for the examined units, reverse engineering has been carried out to gather details of the designs. A concept for the first unit has been developed, in which improved design solutions has been introduced and a number of changes have been implemented in order to minimize material consumption and to adapt the design for AM. The concept has been evaluated by the use of numerical methods. Costs and build time have also been estimated for the developed concept. This project has illustated that it is feasable to manufacture spare parts by the use of AM. The developed concept demonstrates several improvements that are not possible to achieve with conventional manufacturing processes. Nevertheless, a number of limitations such as insufficient build volume, costs as well as time cosuming engineering effort and post-proccessing methods are present for AM. These restrictions, in combination with lack of 3D-models, limits the possibility to make use of the technology. However, the future looks bright, if the technology continues to develop and if subcontractors are willing to adapt to AM it will probably have a major breakthrough within the windpower industry. / Additiv tillverkning, "additive manufacturing" (AM) eller 3D-printing är en automatiserad tillverkningsmetod där komponenten byggs lager för lager från en fördefinierad 3D datormodell. Till skillnad från konventionella tillverkningsmetoder där en stor mängd material ofta bearbetas bort, använder AM nästintill endast det material som komponenten består utav. Förutom materialbesparingar, har metoden ett flertal andra potentiella fördelar. Två av dessa är (1) en stor designfrihet vilket möjliggör produktion av komplexa geometrier och (2) en möjlighet till en förenklad logistikkedja eftersom komponenter kan tillverkas vid behov istället för att lagerföras. Detta examensarbete har utförts på Vattenfall Vindkraft och har till syfte att undersöka om det är möjligt att tillverka och/eller reparera en eller två reservdelar genom AM och om det i så fall kan införa några praktiska fördelar. En kartläggning av komponenter med hög felfrekvens och/eller som kan vara lämpade för AM har genomförts. Av dessa har en roterande oljekoppling även kallad roterskarv valts ut för vidare analys. En omfattande bakgrundsstudie har utförts. En nulägesorientering inom området AM för metaller redogörs, här redovisas även en generell jämförelse mellan konventionella och additiva tillverkningsmetoder. Vidare behandlas aktuella och framtida användningsområden för AM inom vindkraftsindustrin. I bakgrundsstudien behandlas också arbetssättet "reverse engineering", huvudkomponenter i ett vindkraftsverk inklusive roterskarven samt flödesdynamik. Under arbetets gång har en roterskarv med sämre driftshistorik undersökts. I syfte att finna andra konstruktionslösningar som bidrar till en säkrare drift har en bättre presenterande enhet från en annan tillverkare granskats. Då viss detaljteknisk data och konstruktionsunderlag saknas för de undersökta enheterna har "reverse engineering" tillämpats. Ett koncept har sedan utvecklats för den första enheten där förbättrade konstruktionslösningar har introducerats samtidigt som en rad konstruktionsförändringar har gjorts i syfte att minimera materialåtgången och samtidigt anpassa enheten för AM. Konceptet har sedan evaluerats med hjälp av numeriska beräkningsmetoder. För det givna konceptet har även kostnad och byggtid uppskattats. Arbetet visar på att det är möjligt att ta fram reservdelar till vindkraftverk med hjälp av AM. Det framtagna konceptet visar på ett flertal förbättringar som inte kan uppnås med konventionella tillverkningsmetoder. Emellertid finns det en rad begränsningar såsom otillräcklig byggvolym, kostnader och tidskrävande ingenjörsmässigt arbete och efterbehandlingsmetoder. Dessa förbehåll i kombination med avsaknad av 3D-modeller begränsar möjligheterna att nyttja tekniken i dagsläget. Framtiden ser dock ljus ut, om tekniken fortsätter att utvecklas samtidigt som underleverantörer är villiga att nyttja denna teknik kan AM få ett stort genombrott i vindkraftsindustrin.

A study is presented of the instability mechanisms of a damped axisymmetric circular disk of uniform thickness rotating about its axis with constant angular velocity and subjected to various transverse space-fixed loading systems. The natural frequencies of spinning floppy disks are obtained for various nodal diameters and nodal circles with a numerical and an approximate method. Exploiting the fact that in most physical applications the thickness of the disk is small compared with its outer radius, we use their ratio to define a small parameter. Because the nonlinearities appearing in the governing partial-differential equations are cubic, we use the Galerkin procedure to reduce the problem into a finite number of coupled weakly nonlinear second-order equations. The coefficients of the nonlinear terms in the reduced equations are calculated for a wide range of the lowest modes and for different rotational speeds. We have studied the primary resonance of a pair of orthogonal modes under a space-fixed constant loading, the principal parametric resonance of a pair of orthogonal modes when the disk is subject to a massive loading system, and the combination parametric resonance of two pairs of orthogonal modes when the excitation is a linear spring. Considering the case of a spring moving periodically along the radius of the disk, we show how its frequency can be coupled to the rotational speed of the disk and lead to a principal parametric resonance. In each of these cases, we have used the method of multiple scales to determine the equations governing the modulation of the amplitudes and phases of the interacting modes. The equilibrium solutions of the modulation equations are determined and their stability is studied. / Master of Science

We report on low resolution (R~3000) spectropolarimetry of the A0 supergiant star HD 92207. This star is well-known for significant spectral variability. The source was observed on seven different nights spanning approximately 3 months in time. With a rotation period of approximately 1 year, our data covers approximately a quarter of the star's rotational phase. Variability in the continuum polarization level is observed over this period of time. The polarization across the Halpha line on any given night is typically different from the degree and position angle of the polarization in the continuum. Interestingly, Hbeta is not in emission and does not show polarimetric variability. We associate the changes at Halpha as arising in the wind, which is in accord with the observed changes in the profile shape and equivalent width of Halpha along with the polarimetric variability. For the continuum polarization, we explore a spiral shaped wind density enhancement in the equatorial plane of the star, in keeping with the suggestion of Kaufer etal (1997). Variable polarization signatures across Halpha are too complex to be explained by this simple model and will require a more intensive polarimetric follow-up study to interpret properly.

<p dir="ltr">Rotating detonation engines (RDEs) are a promising technology by which to increase the efficiency of propulsion and power generation systems. Self-sustained, rotating detonation waves within the combustion chamber provide a means for combustion to occur at elevated local pressures, theoretically resulting in hotter temperature product gas than a constant pressure combustion process could provide at equivalent operating conditions. Despite theoretical advantages of RDEs, the thermodynamic benefit has yet to be achieved in experimental applications. Additionally, much of the experimental work to date has been conducted at mean operating pressures lower than industrial applications will require, especially for rocket or gas turbine combustion environments. The sensitivity of these devices to operating pressure has made clear the importance of chemical reaction rates on the successful operation of these combustors. This work addresses critical risks associated with implementing this technology at flight-relevant conditions by advancing the understanding of deflagrative loss mechanisms on delivered performance and by investigating the coupling between chemical kinetic timescales and operating modes produced by the combustor.</p><p dir="ltr">A novel pressure measurement technique was developed in which the stagnation pressure of exhausting gas produced by the RDC is measured through quantification of the under-expanded exhaust plume divergence angle at megahertz-rates. Time-averaged stagnation pressure measurements obtained with this technique are shown to be within 1.5% of the equivalent available pressure (EAP) measured. Time-resolved stagnation pressure measurements produced by this technique provide a means to quantify the detonation cycle pressure ratio. It was shown that increasing the total mass flow rate through the combustor, therefore increasing the mean operating pressure, results in a decrease in both detonation wave velocities and detonation cycle stagnation pressure ratios.</p><p dir="ltr">Numerical modeling of detonations was conducted to understand the coupling of stagnation pressure ratios and wave speeds to deflagrative modes of combustion within rotating detonation combustors. Using the experimental measurements, it is shown that significant amounts of propellant combusts as a result of deflagration prior to (i.e., preburning) and after (i.e., afterburning) the detonation wave. Increasing the RDC operating pressure by 4x is shown to increase the amount of preburned propellant by 4.5x. Relevant chemical kinetic reaction rates of the conditions tested are modeled to increase by 4.5x as well, indicating that the increase in reactant preburning is the result of faster chemical kinetic timescales associated with higher pressure combustion. Results from this testing suggest an operating pressure upper limit for this combustor exists around 20 bar. At these conditions, chemical kinetic rates would be fast enough that deflagration would be the primary mode of combustion and the detonation would not exist. It is suggested that different injector or combustor designs might be able to extend operating limits, however it is unclear if there is a chemical kinetic limit at which no design would be able to overcome.</p><p dir="ltr">Despite significant amounts of deflagrative combustion within the RDC, the vacuum specific impulse produced by the RDC was shown to be between 95.0% and 98.5% of what an ideal deflagrative combustor could produce for most conditions. Given conventional rocket combustors typically operate at specific impulse efficiencies in the range of 90%-99%, it is noted that the RDC tested in this work has demonstrated, at the very least, equal performance to the current state of the art for rocket propulsion combustors while utilizing an effective combustor length (L*) of only 63 mm (2.5 inches). A detailed RDC performance model was developed which considered losses associated with deflagration (both preburning and afterburning) and incomplete combustion. Using measurements obtained from the experiment it is determined that incomplete combustion contributes a larger performance loss than the deflagration which occurs within the combustor.</p><p dir="ltr">A total of 17 parametric studies were conducted experimentally to evaluate the response of the RDC specifically to changes in the propellant chemical reaction timescales. Detonation wave arrival times ranged between 10 microseconds and 178 microseconds as a result of testing at ranges of operating pressures, equivalence ratios, and utilizing nine unique propellant combinations. It was shown that the wave arrival time is primarily a function of chemical kinetic timescales and injector mixing processes. A model using the injector momentum ratio and modeled deflagrative preheat times is shown to be able to closely predict experimentally obtained detonation wave arrival times.</p>