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In dilute polymer solution, polymers are able to change the flow structures and suppress the intensity of turbulence, resulting in a considerable friction drag reduction (DR). Despite the extraordinary progress made in the past few decades, some critical questions remain unanswered. This dissertation will try to address two fundamental questions in dilute polymeric turbulence: (I) interactions between polymers and turbulent motions during the qualitative low-extent to high-extent drag reduction (LDR and HDR) transition in inertia-driven turbulence, (II) roles of the inertia- and elasticity-driven turbulent motions in the dynamics of high elasticity polymeric flows. Many studies in the area of DR turbulence have been focused on the onset of DR and the maximum drag rection (MDR) asymptote. Between these two distinct stages, polymeric turbulent flows can also be classified into the qualitative LDR and HDR stages. Understanding the polymer-turbulence interactions during the drastic LDR-HDR transition is of vital importance for the development of efficient flow control technology. However, knowledge regarding this qualitative transition is still limited. In our DNS (direct numerical simulation) study, differences between the LDR and HDR stages are presented by a number of sharp changes in flow structures and statistics. Drag reduction in the flows is thus governed by two different mechanisms. The first is introduced at the onset of DR, which has been well explained by the indiscriminate suppression of turbulent fluctuations during the coil-stretch transition of polymers. The second mechanism starts at the LDR-HDR transition but its physical origin is not clear. Based on instantaneous observations and indirect statistical evidence, we proposed that polymers, after the LDR-HDR transition, could suppress the lift-up process of the near-wall vortices and modify the turbulent regeneration cycles. However, direct evidence to support this hypothesis is not available without a statistical analysis of the vortex configurations. Therefore, a new vortex tracking algorithm -- VATIP (vortex axis tracking by iterative propagation) -- is developed to analyze statistically the configurations and distribution of vortices. Implementing this method in the polymeric turbulence demonstrates that the lift-up process of streamwise vortices in the buffer layer is restrained at HDR, while the generation of hairpins and other three-dimensional vortices is suppressed. In addition, the characteristic lifting angle of conditional eddies extracted by a conditional sampling method is found to be larger in HDR than in the Newtonian turbulence. These observations all support our hypothesis about the mechanism of LDR-HDR transition. Research on the low elasticity turbulence usually considered the flow motions to be Newtonian-like. Turbulence here is driven by the inertial force (and hence called ``inertia-driven'' turbulence (IDT)) while polymers are responsible for dissipating turbulent kinetic energy. In the high elasticity turbulence, recent studies found a completely different turbulent flow type in which turbulence is driven by the elastic force and polymers could also feed energy to the flow. The behaviors of this ``elasticity-driven'' turbulence (EDT) are of significant interest in this area because of its potential connection to the MDR asymptote. However, EDT is difficult to capture by the traditional pseudo-spectral DNS scheme (SM) as a global artificial diffusion (GAD) term is involved in the polymer constitutive equation to stabilize the simulation. In our study, a new hybrid pseudo-spectral/finite-difference scheme is developed to simulate the polymeric turbulence without requiring a GAD. All of the spatial derivative terms are still discretized by the Fourier-Chebyshev-Fourier pseudo-spectral projection except for the convection term in the constitutive equation which is discretized using a conservative second-order upwind TVD (total variation diminishing) finite difference scheme. The numerical study using the hybrid scheme suggests that turbulent flows can be either driven by the inertial or the elastic forces and respectively result in the IDT and EDT flows. A dynamical flow state is also found in the high elasticity flow regime in which IDT and EDT can be sustained alternatively. / Thesis / Doctor of Philosophy (PhD) / Turbulence is known to consume kinetic energy in a fluid system. To enhance the efficiency of fluid transportation, various techniques are developed. Especially, it was found that a small amount of polymers in turbulent flows can significantly suppress turbulent activity and cause considerable friction drag reduction (DR). Extraordinary progress has been made to study this phenomenon, however, some questions still remain elusive. This dissertation tries to address some fundamental questions that relate to the two typical polymeric turbulent motions: the inertia- (IDT) and elasticity-driven turbulence (EDT). In IDT, mechanisms of transitions between the intermediate stages are investigated from the perspective of vortex dynamics. The different effects of polymers at each stage of the flow lead to different flow behaviors. Particularly, starting from the low- to high-extent DR transition, the lift-up process of vortices is suppressed by polymers. The regeneration cycles of turbulence are thus modified, which results in qualitative changes of flow statistics. Numerical study on EDT is enabled by a newly developed hybrid pseudo-spectral/finite-difference scheme. A systematic investigation of the parameter space indicates that EDT is one self-contain turbulence driven purely by the elastic force. It can also interact with IDT and lead to a dynamical flow state in which EDT and IDT can alternatively occur.

The objective of this study is to characterize the mechanism of drag reduction by comparing the dynamical eigenfunctions of a turbulent pipe flow against those of two known cases of drag reduced flows. The first is forced drag reduction by spanwise wall oscillation, and the second is natural drag reduction found in relaminarizing flow. The dynamics are examined through a Karhunen-Lo`eve (KL) expansion of the direct numerical simulation flow field results. The direct numerical simulation (DNS) is performed using NEK5000, a spectral element Navier-Stokes solver, the first exponentially convergent investigation of DNS of turbulence in a pipe. The base flow is performed at a Reynolds number of Re = 150, resulting in a KL dimension of D_KL = 2130. As in turbulent channel flow, propagating modes are found, characterized with constant phase speed, and contribute of 80.58% of the total fluctuating energy. Based upon wavenumber characteristics and coherent vorticity visualization, four subclasses of propagating modes and two subclasses of non-propagating modes are discovered, qualitatively similar to the horseshoe (hairpin) vortex structure reported in literature. The drag reduced case is performed at the same Reynolds number with a spanwise velocity A+ = 20, a period of T+ = 50, and is driven by a constant pressure gradient. This results in a increase of flow rate by 27 %, and the KL dimension is reduced to D_KL = 102, a 96% reduction. The propagating modes, in particular the wall modes, are pushed away from the wall, resulting in a 34% increase in their advection speed, and a shift away from the wall of the root-mean-square and Reynolds stress peaks. The relaminarizing case observes the chugging motion of the mean flow rate when the Reynolds number is barely turbulent, at Re = 95. This chugging motion is the relaminarization of the flow, resulting in an increased flow rate, and then before complete relaminarization, the flow regains its turbulent state. This occurs because the lift modes, which are responsible for the majority of the energy in the inertial range of the energy spectra, decrease by two or three orders of magnitude. The chugging ends when the wall modes restart the turbulent cascade, and the lift modes are repopulated with energy. A model for the energy path is developed, with energy going from the pressure gradient to the shear modes, then to the roll modes, then to the wall modes, and then finally to the lift modes. It is concluded that drag reduction in a flow can be achieved by disrupting any leg of this model, thus disrupting the self-sustaining mechanism of turbulence. The spanwise wall oscillation shortened the life span of the wall modes, thus limiting their ability to pass energy to the lift modes. Likewise, the low Reynolds number did not provide enough energy to sustain the lift modes, and so relaminarization began. The contribution of this work is twofold. Firstly, the structure of turbulent pipe flow is examined and visualized for the first time using the Karhunen-Lo`eve method. The second, and perhaps greatest contribution of this work, is that the mechanism of drag reduction has been characterized as the link between the wall modes and the lift modes. This will allow future work on developing real methods of drag reduction, and eventually porting it to high Reynolds number flows, like that of an oil pipeline at Re= 40, 000. To achieve this, certain questions remain to be answered, such as what is the most efficient method of disrupting the wall-lift mechanism? Is there a single structure that can be identified and manipulated that gives a similar eect? Once answered, this will allow for a new generation of pipelines to be developed, and considering the implications in petroleum industry alone, will result in a significant contribution to the economy of the world. / Ph. D.

Three tree species, Freeman maple (Acer x. freemanii), swamp white oak (Quercus bicolor (Willd.)) and shingle oak (Quercus imbricaria (Michx.)) were tested before and after pruning to determine the effectiveness of pruning on reducing drag and bending moment. Pruning methods were thin, reduce and raise and meet the requirements set by the American National Standard Institute A300 standards for Tree Care Operations Trees, Shrub, and Other Woody Plant Maintenance - Standard Practices (Pruning). Trees were tested up to speeds of 22.4m*s-1 over 1.6km by driving them in the bed of a truck. Drag, based on a centroid of the crown, and a bending moment was calculated. Drag and bending moment were also normalized by tree mass and crown area. Reduction pruning worked more effectively for Freeman maple and raise pruning for swamp white oak at reducing drag. Simple to measure tree characteristics were analyzed to determine the best predictors of drag and bending moment in the field. Tree mass frequently was the best predictor of drag and bending moment. Information should be used with caution due to the fact that the trees tested were small stature and a limited number of trees were tested. / Master of Science

An experimental program was conducted at NASA Langley Research Center, in Hampton Virginia, that included development and evaluation of an operational facility for wall drag measurement and evaluation of the total drag of various wall configurations. The drag of three possible supersonic combustor wall configurations was measured to determine if reduction in skin friction and/or wave drag could be achieved through the use of cavities, vented cavities, and/or mass addition. Data are presented herein as average drag force, wall static pressure distributions and focusing schlieren images. The experimental model consisted of a series of interchangeable aluminum plates attached to an air-bearing suspension system. The system was equipped with load cells that measured forces up to 10 pounds in the drag direction only. The plates were exposed to a Mach 2 air stream at a total pressure of 115 psia. This flow field contained a train of relatively weak, unsteady, reflecting shock waves that were produced by the Mach 2 nozzle and plenum chamber assembly. Mass addition was successfully employed to alter the plate drag in both the transpiration and cavity configurations. Three plate configurations were tested: a flat plate, a plate with air transpiration, and a cavity plate equipped for the introduction of bleed air into the cavity. The resulting data base consists of drag data at Mach 2 for a standard flat plate, and two wall configurations tested with bleed mass flow rates ranging from 0.00 to 0.06 lbm/sec. The experimental wall static pressure distributions and the focusing schlieren images are shown to compare favorably with the CAN-DO computer analysis results. / Master of Science

Presented in this paper are experiments to test the hypothesis that drag reduction is possible over hydrophobic surfaces in the Wenzel state during laminar and turbulent flows. Quantification of surface drag reduction in rectangular channel flow over walls with specific hydrophobic or hydrophilic properties was obtained with pressure drop measurements along the channel for a range of Reynolds numbers between 350 and 5900. Several commercially available materials and coatings were chosen in order to span a range of contact angles between 30° and 135°. The results are within the bounds of the theoretical values calculated with the Colebrook equation, and do not show any reduction in wall shear stress as a function of material properties or surface chemistry. The differences between this experiment and others measuring pressure drop over hydrophobic surfaces is the macro-scale conditions and the hydrophobic surfaces being fully wetted. These experiments are further proof of the importance of a liquid-vapor interface for increasing the shear free area to produce drag reduction. / Master of Science

A research effort aimed at enhancing ACSYNT, a computer program for aircraft conceptual design, has necessitated the development of methods for predicting inlet drag. Originally, the drag of only one inlet type, the variable-geometry conical inlet, could be calculated within ACSYNT. This prompted the present research which resulted in the creation of a modular suite of subroutines that extend the capability of ACSYNT. Using this new source code, ACSYNT can now predict the drag of subsonic and supersonic pitot inlets, fixed- and variable-geometry conical inlets, and two-dimensional supersonic inlets. Even though the requirement of computational efficiency has necessitated that many simplifications be made in the analysis, the drag calculations have a sound physical basis. The semi-empirical methods have been extracted from a number of sources based on an extensive literature survey, and these have been enhanced to encompass the full range of inlet operating conditions. The effectiveness of the methods has been demonstrated by comparing some results of the predictions to published data. / Master of Science

"A study is presented detailing the simulation of a drag-free follow-on mission to NASA’s Gravity Recovery and Climate Experiment (GRACE). This work evaluates controller performance, as well as thrust, power, and propellant mass requirements for drag-free spacecraft operation at orbital altitudes of 160 - 225 kilometers. In addition, sensitivities to thermospheric wind, GPS signal accuracy and availability of ephemeris data are studied. Orbital dynamics were modeled in Matlab and take into account 2 body gravity effects, J2-J6 non-spherical Earth effects, atmospheric drag and control thrust. A drag model is used in which the drag acceleration is a function of the spacecraft’s relative velocity to the atmosphere, and a “drag parameter,” which includes the spacecraft’s drag coefficient and local mass density of the atmosphere. A MSISE-90 atmospheric model is used to provide local mass densities as well as free stream flow conditions for a Direct Simulation Monte Carlo drag analysis used to validate the spacecraft drag coefficient. The controller is designed around an onboard inertial sensor which uses a freely floating reference mass to measure deviations in the spacecraft position, resulting from non-gravitational forces, from a desired target orbit. Thruster (control actuator) models are based on two different Hall thrusters for providing the orbital along-track acceleration, colloid thrusters for the normal acceleration, and a miniature xenon ion thruster (MiXI) for the cross-track acceleration. The most demanding propulsion requirements correspond to the lowest altitude considered, 160 kilometers. At this altitude the maximum along-track thrust component is calculated to be 98 millinewtons with a required dynamic (throttling) response of 41 mN/s. The maximum position error at this altitude was shown to be in the along-track direction with a magnitude of 3314.9 nanometers and a peak spectral content of 1800 nm/sqrt(Hz) at about 0.1 Hz. At 225 kilometers, the maximum along-track thrust component reduces to 10.3 millinewtons. The maximum dynamic response at this altitude is 4.23 mN/s. The maximum along-track position error is reduced to 367.9 nanometers with a spectral content peak of 40 nm/sqrt(Hz) at 0.1 Hz. For all altitudes, the maximum state errors increase as the mission length increases, however, higher altitude missions show less of a maximum displacement error increase over time than those of lower orbits. The ability of a colloid thruster to control the normal drift is found to be dependent on how frequently the spacecraft state data is updated. Reducing the period between updates from 10 seconds to 1 second reduces the maximum normal state error component from 199 nanometers to less than 32 nanometers, suggesting that spacecraft state update frequency could be a major driver in keeping the spacecraft on the target trajectory. Sensitivity of maximum required thrust and accumulated sensor error to measurement uncertainty is found to be less of a driver than state update frequency. A ‘worst case” thermospheric wind gust was modeled to show the increase on propulsion requirements if such an event were to occur. At 200 kilometers, maximum winds have been measured to be in increase of 650 m/s in the westward direction in the southern pole region. Assuming the majority of the 650 m/s gust occurs over a 4 second time span, the maximum required cross-track thrust at 200 kilometers increases from 1.12 to 2.01 millinewtons. This large increase may drive the thruster choice for a drag-free mission at a similar altitude. For the spacecraft point design considered with a propellant mass fraction of 0.18, the mission lifetime for the 160 km case was calculated to be 0.76 years. This increases 2.27 years at an altitude of 225 km."

O gênero é uma construção social, entretanto, ainda hoje ele é compreendido através de uma visão essencializadora e naturalizadora que se baseia em um aparato de saberes biológicos para reiterar a existência de um alinhamento entre gênero, sexo, prática sexual e desejo. Se enquadrar nesse alinhamento significa estar em consonância com as normas vigentes na nossa sociedade, e todos(as) aqueles(as) que fogem ou provocam nele deslocamentos são tidos(as) como inferiores e indesejáveis, não sendo reconhecidos como seres inteligíveis e estando, então, passíveis de exclusão. O objetivo principal desse estudo constitui em compreender a relação entre a construção parodística das personagens Drag Queens e a construção social dos papéis de gênero, dando prosseguimento à tentativa de desvendar as trajetórias e as compreensões sobre o gênero em pessoas que se encontram fora dos limites impostos pela lógica binária que valida apenas a existência do masculino e feminino, colocando-os como opostos e passíveis de categorização.2 Através do ato estético-político da construção da figura da Drag Queen acredita-se ser possível estar e cruzar a fronteira dos gêneros, tendo uma identidade ambígua ou indefinida e explicitando o caráter artificialmente imposto das identidades fixas, sendo um meio para mapear dispositivos que funcionem em prol da ruptura das ontologias e possibilitem outras formas de vivências que resistam às categorizações socialmente construídas, trazendo potência para a promoção de uma multiplicidade de possibilidades de existência / The term gender is a \"social construction\", however, it\'s still currently understood through an essential and naturalizing vision which is based on an apparatus of biological knowledges to reaffirm the existence of an alignment between gender, sexual orientation, sexual intercourse and desire. Fitting in with such alignment means being in consonance with actual social standards, and all those who avoid or arouse displacements are considered smaller and unwanted, not being recognized as intelligible human beings and, thus, being subject to exclusion. The main goal of this thesis consists on building a relation between the travesty/burlesque construction of the Drag Queens\' characters and the social construction of gender roles, continuing on in the attempt to unravel trajectories and understandings regarding the gender of people who find themselves outside the limits imposed by the binary logic which only validates the existence of male and female genders, placing them as opposites and eligible for categorization3. Through the aesthetic-political act of the construction of the Drag Queen\'s figure it\'s believed it\'s possible to be on and across the genders\' border, possessing an ambiguous or undefined identity and exposing the artificially imposed character of the fixed ones, therefore being a way of mapping devices that work for the rupture of ontologies and enable other ways of living which are able to stand up to socially constructed categorizations, bringing about enough power to promote the plurality of other possible existences