abstract: Tesla turbo-machinery offers a robust, easily manufactured, extremely versatile prime mover with inherent capabilities making it perhaps the best, if not the only, solution for certain niche applications. The goal of this thesis is not to optimize the performance of the Tesla turbine, but to compare its performance with various working fluids. Theoretical and experimental analyses of a turbine-generator assembly utilizing compressed air, saturated steam and water as the working fluids were performed and are presented in this work. A brief background and explanation of the technology is provided along with potential applications. A theoretical thermodynamic analysis is outlined, resulting in turbine and rotor efficiencies, power outputs and Reynolds numbers calculated for the turbine for various combinations of working fluids and inlet nozzles. The results indicate the turbine is capable of achieving a turbine efficiency of 31.17 ± 3.61% and an estimated rotor efficiency 95 ± 9.32%. These efficiencies are promising considering the numerous losses still present in the current design. Calculation of the Reynolds number provided some capability to determine the flow behavior and how that behavior impacts the performance and efficiency of the Tesla turbine. It was determined that turbulence in the flow is essential to achieving high power outputs and high efficiency. Although the efficiency, after peaking, begins to slightly taper off as the flow becomes increasingly turbulent, the power output maintains a steady linear increase. / Dissertation/Thesis / M.S. Mechanical Engineering 2012

The main objective of the thesis is to provide a detailed assessment of the performance of four types of Low Reynolds Number (LRN) Eddy Viscosity Models (EVM), widely used for industrial purposes, on flows featuring SWBLI, using experimental and direct numerical simulation data. Within this framework the two-equation linear k-ε of Launder and Sharma (1974) (LS), the two-equation linear k-ω SST, the four-equation linear φ-f of Laurence et al. (2004) (PHIF) and the non-linear k-ε scheme of Craft et al. (1996b,1999) (CLSa,b) have been selected for testing. As initial test cases supersonic 2D compression ramps and impinging shocks of different angles and Reynolds numbers of the incoming boundary layer have been selected. Additional test cases are then considered, including normal shock/isotropic turbulence interaction and an axisymmetric transonic bump, in order to examine the predictions of the selected models on a range of Mach numbers and shock structures. For the purposes of this study the PHIF and CLSa,b models have been implemented in the open source CFD package OpenFOAM. Some results from validation studies of these models are presented, and some explorations are reported of certain modelled source terms in the ε-equation of the PHIF and CLSb models in compressible flows. Finally, before considering the main applications of the study, an examination is made of the performance of different solvers and numerical methods available in OpenFOAM for handling compressible flows with shocks. The performance of the above models, is analysed with comparisons of wall-quantities (skin-friction and wall-pressure), velocity profiles and profiles of turbulent quantities (turbulent kinetic energy and Reynolds stresses) in locations throughout the SWBLI zones. All the selected models demonstrate a broadly consistent performance over the considered flow configurations, with the CLSb scheme generally giving some improvements in predictions over the other models. The role of Reynolds stress anisotropy in giving a better representation of the evolution of the boundary layer in these flows is discussed through the performance of the CLSb model. It is concluded that some of the main deficiencies of the selected models is the overestimation of the dissipation rate levels in the non-equilibrium regions of the flow and the underestimation of the amplification of Reynolds stress anisotropy, especially within the recirculation bubble of the flows. Additionally, the analysis of the performance of the considered EVM's in a normal shock/isotropic turbulence interaction illustrates some drawbacks of the EVM formulation similar to the ones observed in normally-strained incompressible flows. Finally, a hybrid Detached Eddy Simulation (DES) approach is incorporated for the prediction of the transonic buffet around a wing.

No description available.

Like virtually every other human activity, air transport has an impact on the environment and similar to all other industries environmental impacts and economic issues are exerting more pressure on aircraft sector to meet the demands and implicated conditions. Secondly in today’s competitive industrial performance index new modern techniques are being introduced to improve the aerodynamics so that the efficiency of the newly designed aircrafts could be enhanced. The active flow control techniques have been proved vital towards achieving more effective air flow on the aircraft wing and that eventually helps to increase the lift coefficient at full scale flight. Synthetic jet actuators have been experimentally proved a promising technique towards achieving flow separation delay on the surface they have been deployed on. For the operation the synthetic jet actuators offer a unique characteristic in that they make use of the ambient work fluid and that deny the need of any extra fluid from outside the system and that helps in two fold. Firstly the need to make additional arrangements for air supply through the complex piping system has been ruled out completely. Secondly in the system the addition of any new weight that usually associates with the introduction of any new technique has been avoided. In this work firstly the dye visualization technique is used to study the interaction of the synthetic jet with both types of boundary layers that is laminar and turbulent. Secondly PIV measurements are performed to quantitatively analyze the evolution of vortical structures in the boundary layer. The aim is to understand the fluid dynamics involved in the interaction of the vortical structures with the neal wall fluid that ultimately re-attach the flow with the surface. Lastly an artificial flow separation is generated on the deflected flat plate surface and the synthetic jet is deployed to observe the separation delay on the surface. Various vortical structures have been generated by operating the actuator at varying parameters and issued into the boundary layer upstream of the separation line. The effectiveness of each type of vortices has been evaluated quantitatively to work out the optimum parameters at which the actuator must be operated to achieve the best control effect at the given free-stream condition.

The surface character of a suburban area is far from the uniform, smooth and flat planes over which current surface-layer theory is valid and where vertical eddy-fluxes can be assumed to be almost constant horizontally and vertically. The complexity of the surface introduces considerable variability into the atmosphere at small spatial scales. This variability is partly reduced and spatially-averaged by turbulent mixing but still leaves the concerns about the spatial representativeness of sensible heat flux measurements over a suburban area. The spatial scales of sensible heat flux variability are discussed in terms of the distribution of surface temperature and roughness elements. It is shown that : (1) an eddy-correlation measurement can be considered spatially representative, if its surface zone of influence (source area) is large enough to include a spatially representative sample of surface temperature and roughness elements. (2) a quantitative measure of spatial representativeness can be estimated by use of the two-dimensional Fourier transform of the surface temperature and roughness element distributions (i.e. by the normalized integrated variance spectrum). (3) the source area of an eddy correlation measurement may be evaluated by a numerical model based on a probability density function plume diffusion model. The source area model developed herein can also be used to estimate the relative influence of specific surface sources or sinks upon an eddy-flux measurement in the surface layer. These concepts are tested in a suburban residential area in Vancouver, B.C., Canada. Remotely sensed surface temperatures and a digitized roughness element inventory are used as data-bases for the Fourier transforms to develop representativeness criteria for eddy-flux measurements. A set of sensible heat flux measurements at six sites and the corresponding source area calculations are used to formulate recommendations for the objective evaluation of the spatial representativeness of sensible heat flux measurements over a suburban area. The validity of the suggested evaluation methods is confirmed by the observations. Internal boundary layer growth, estimated by the source area model, compares well with existing work. Some consequences of complex surfaces on the surface layer structure are briefly discussed. / Arts, Faculty of / Geography, Department of / Graduate

Detonations in gases usually propagate with lateral strain rates, in either weakly confined or varying-cross-section or curved or even small-sized geometries. Lateral strain rates have been generally known to significantly impact the detonation dynamics, i.e., decreasing the propagation speeds lower than the theoretical Chapman-Jouguet (CJ) velocities, increasing the propagation limit pressures as well as cell sizes. Since the detonation-based engines require the reliable control of the accurate ignition and stable propagation of a detonation wave, it is desirable to have the predictive capability of the response of detonation dynamics to lateral strain rates, for achieving the practical purposes of detonation applications. Therefore, the present thesis aims to provide such predictability, by quantifying the effect of lateral strain rates on detonation dynamics from both the experimental and numerical modelling perspectives. Experimentally, this study extended the exponential horn technique of Radulescu and Borzou (2018) to a range of characteristic mixtures with varied detonation instability levels, i.e., from the weakly unstable system of 2H₂/O₂/7Ar to the highly unstable one of CH₄/2O₂. Steady detonation waves were obtained at the macro-scale, with the very regular H₂/O₂/Ar detonation cellular structures characterized by reactive transverse waves while the unstable hydrocarbon-oxygen detonation reaction zone structures in the presence of significant unreacted gas pockets. The meaningful D-K curves characterizing the relationships between the detonation mean propagation speeds and lateral strain rates were directly obtained from experiments. Comprehensive comparisons were then made between experiments and predictions from the generalized ZND model with lateral strain rates. Excellent agreement was found for the stable H₂/O₂/Ar detonations due to the much longer thermally insensitive reaction zone lengths compared to the characteristic induction zone lengths, while substantial departures exist for the highly unstable CH₄/2O₂ detonations. The degree of departure was found to correlate well with the detonation instability. As compared to the laminar ZND wave, the more unstable hydrocarbon-oxygen detonations manifested themselves in the significantly enhanced global rates of energy release with the notably suppressed thermal character of ignition. Implications of such a globally enhanced burning mechanism highlight the important role of diffusive processes involved in turbulent burning of the unreacted gas pockets. Finally, empirical global reaction rate laws were developed for effectively capturing the dynamics of unstable detonations. Numerically, this work proposed a novel model for evaluating the effect of boundary layer losses on cellular structures of 2D detonations in narrow channels. The boundary-layer-induced lateral strain rate was evaluated using the negative boundary layer displacement of Mirels' theory. With the theoretical Mirels' constant KM reduced by a factor of 2, the experimentally obtained 2H₂/O₂/7Ar detonations can be very well reproduced by simulations using the resulting quasi-2D formulation. It was further found out that detonation cellular cycle dynamics can be modified by the presence of boundary layer losses, yielding larger velocity fluctuations and more rapid decay rates of the lead shock. The exponential sensitivity of detonation cell sizes to velocity deficits, controlled by the global activation energy, highlights the importance of providing the detonation speed when reporting experimentally measured cell sizes.

High speed boundary layers are an important aspect of vehicle design. It is crucial to know whether the boundary layer is laminar, turbulent, or transitional. The heat transfer rate increases dramatically from laminar to turbulent flow, so it must be considered when designing a high speed vehicle. This thesis studied a flared cone geometry with forced direct numerical simulation. This geometry has experimental data collected from a Mach 6 quiet tunnel and previous computational data. A two stage computational procedure is carried out in order to efficiently model the boundary layer. The first stage involved finding a full cone solution and creating an inlet profile. This inlet profile is imposed on the inlet of a 10-degree sector of the flared cone. This is done to achieve the desired resolution while maintaining reasonable computational costs for the DNS. With this setup, the second stage continues with a high-order basic state computation using the inlet profile. After the higher order basic state is computed, random forcing is applied using traveling plane waves to promote transition and the results are analyzed. Linear stability and frequency analysis is conducted and the unstable frequencies match with expected results. Transition is achieved using the forcing and qualitatively matches previous experimental and computational data for the flared cone. Just as in the experiment and previous computations, regions of primary and secondary streaks are found and have similar heat transfer magnitudes. However, the location of these streaks is different and is likely due to the setup of the computation.

Surface pressure fluctuations developed by turbulent flow within a boundary layer is a major cause of flow noise from a body and an issue which reveals itself over a wide range of engineering applications. Modified boundary layers (MBLs) inspired by the down coat of an owl’s wing has shown to reduce the acoustic effects caused by flow noise. This thesis investigates the mechanisms that modified boundary layers can provide for reducing the surface pressure fluctuations in a boundary layer. This study analyzes various types of MBLs in a wall jet wind tunnel through computational fluid dynamics and numerical surface pressure spectrum predictions. A novel surface pressure fluctuation spectrum model is developed for use in a wall jet boundary layer and demonstrates high accuracy over a range of Reynolds numbers. Non-dimensional parameters which define the MBL’s geometry and flow environment were found to have a key role in optimizing the acoustic performance. / Includes bibliography. / Thesis (M.S.)--Florida Atlantic University, 2019. / FAU Electronic Theses and Dissertations Collection

<div>A 7° half-angle cone with a highly-swept fin was tested in the Boeing/AFOSR Mach-6 Quiet Tunnel at 0.0° angle of attack. Previous measurements of the surface heat transfer using temperature sensitive paint revealed heating streaks on the cone surface related to streamwise vortices generated by the fin shock. High-frequency measurements of the cone-surface pressure fluctuations revealed that transition occurs in the streak region at sufficiently-high freestream unit Reynolds numbers under quiet flow. In this work, high-resolution measurements of the surface heat transfer are obtained using infrared thermography and a polyether-ether-ketone wind-tunnel model. In addition, a novel model design made it possible to measure pressure fluctuations throughout the streak region on the cone surface.</div><div><br></div><div>A slender cone with a sharp nosetip and a fin swept back 75° with a 3.18 mm leading-edge radius served as the primary geometry for this work. Two laminar heating streaks</div><div>were measured on the cone surface. These travel along a line of nearly-constant azimuth. A hot spot develops in the streak farthest from the fin, which then moves upstream with increasing freestream Reynolds number. Downstream of this hot spot, the streaks begin to spread in azimuth. The heat transfer along the outer streak shows a threefold increase near the hot spot before decreasing back to nearly two times the laminar streak heating. The amplitude of the pressure fluctuations increases simultaneously with the heat transfer, reaching a peak of nearly 9% of the Taylor-Maccoll pressure for a 7° straight cone. Power spectral densities calculated from these fluctuations demonstrate spectral broadening, which is indicative of boundary-layer transition. Using surface-pressure-fluctuation and heat-flux measurements, transition onset was estimated to occur at an axial length Reynolds number of 2.2×10⁶. Pressure sensors that were rotated through the streak region showed that multiple instabilities amplify between the heating streaks, upstream of the transition onset location. Downstream of transition onset, the highest-amplitude instabilities are localized to the hot spot in the outer streak. The effect of freestream noise on transition was also investigated with this geometry. Under conventional noise levels, transition onset was estimated to occur at an axial length Reynolds number of 0.93×10⁶, and only one instability was measured in the streak region with a frequency similar to the second-mode instability.</div><div><br></div><div>Four configurations were tested to investigate the effect of fin sweep and nosetip bluntness under quiet flow. Fins with 70° and 75° sweep were each tested with nominally sharp and 1-mm-radius nosetips. Increasing fin sweep was shown to move the heating streaks on the cone closer to the fin and to decrease the peak-to-peak spacing of the streaks. In addition, transition onset occurred at lower freestream unit Reynolds numbers for the 70° sweep case. Increasing nosetip radius had little effect on the heating streaks, other than to delay the transition location. A blunt nosetip was shown to delay transition more for the 75° sweep fin as compared to the 70° fin. Similar instabilities were measured for all four of the configurations in this work. The frequency of the instabilities appears to be correlated with the peak-to-peak distance of the heating streaks, which can be viewed as an indirect measurement of the vortex diameter.</div><div><br></div><div>Lastly, the first quantitative measurements of heat transfer on the fin were made using the infrared thermography apparatus. Peak heating on the fin, not including the leading edge, is lower than peak heating rates on the cone. One broad heating streak was measured close to the corner, and smaller low-heating streaks were measured farther outboard. The heating within the streak closest to the corner was shown to agree well with a fully-laminar computed basic state, indicating that the flow on the fin is laminar up to at least 6.31×10⁶ m⁻¹. Using miniaturized Kulite sensors, pressure fluctuations were measured at twelve locations on the fin surface. No obvious conclusions could be drawn from these Kulite measurements, and there is no clear indication that transition occurs on the fin within the maximum quiet</div><div>freestream conditions.</div>

Die vorliegende Arbeit widmet sich der, vorwiegend experimentellen, Untersuchung der Wirkung wandparalleler Lorentzkräfte in Strömungsrichtung auf Grenzschichtprofile und Körperumströmungen. Die Themen - Beeinflussung der Grenzschicht an ebenen Platten mit stationären Lorentzkräften - Kontrolle von Strömungsablösungen an Zylindern und symmetrischen Profilen mit stationären Lorentzkräften - Beeinflussung von Zylindernachläufen und abgelösten Tragflügelumströmungen mit zeitlich periodischen Lorentzkräften werden behandelt.