Yes / This review paper addresses the structure of the mean flow and key turbulence quantities in free-surface flows with emergent vegetation. Emergent vegetation in open channel flow affects turbulence, flow patterns, flow resistance, sediment transport, and morphological changes. The last 15 years have witnessed significant advances in field, laboratory, and numerical investigations of turbulent flows within reaches of different types of emergent vegetation, such as rigid stems, flexible stems, with foliage or without foliage, and combinations of these. The influence of stem diameter, volume fraction, frontal area of stems, staggered and non-staggered arrangements of stems, and arrangement of stems in patches on mean flow and turbulence has been quantified in different research contexts using different instrumentation and numerical strategies. In this paper, a summary of key findings on emergent vegetation flows is offered, with particular emphasis on: (1) vertical structure of flow field, (2) velocity distribution, 2nd order moments, and distribution of turbulent kinetic energy (TKE) in horizontal plane, (3) horizontal structures which includes wake and shear flows and, (4) drag effect of emergent vegetation on the flow. It can be concluded that the drag coefficient of an emergent vegetation patch is proportional to the solid volume fraction and average drag of an individual vegetation stem is a linear function of the stem Reynolds number. The distribution of TKE in a horizontal plane demonstrates that the production of TKE is mostly associated with vortex shedding from individual stems. Production and dissipation of TKE are not in equilibrium, resulting in strong fluxes of TKE directed outward the near wake of each stem. In addition to Kelvin–Helmholtz and von Kármán vortices, the ejections and sweeps have profound influence on sediment dynamics in the emergent vegetated flows.

A comprehensive computational and experimental analysis has been conducted to characterize the flow dynamics and periodic structures formed in the wake of complex turning vanes. The vane packs were designed by the StreamVane swirl distortion generator technology, a design system that can efficiently reproduce swirl distortion for compressor rig and full turbofan engine testing. StreamVanes consist of an array of turning vanes that commonly contain variations in turning angle along their span, a nonaxisymmetric profile about the centerline, and vane-to-vane intersections or junctions to accurately generate the desired distortion. In this study, vane packs are considered complex if they contain two out of three of these features, a combination seen in other turbomachinery components outside of StreamVane design. Similar to all stator vanes or rotor blades, StreamVane vane packs are constructed using a series of cross-sectional airfoil profiles with blunt trailing edges and finite thicknesses. This, in turn, introduces periodic vortex structures in the wake, commonly known as trailing edge vortex shedding. To fully understand how the dynamics and coherent wake formations within vortex shedding impact both the flow distortion and structural durability of StreamVanes, it is first necessary to characterize the corresponding wakes in three dimensions. The current study provides an in-depth analysis to predict and measure the trailing edge vortex development using high-fidelity computational fluid dynamics and stereoscopic time-resolved particle image velocimetry experiments. Two testcase StreamVane geometries were specifically designed with complex features to evaluate their influence on the dynamics and coherence of the respective vane wakes. Fully three-dimensional, unsteady computational fluid dynamics simulations were performed using a Reynolds-Averaged Navier-Stokes solver coupled with a standard two-equation turbulence model and a hybrid, scale-resolving turbulence model. Both models predicted large-scale wake frequencies within 1—14% of experiment, with a mean difference of less than 3.2%. These comparisons indicated that lower fidelity simulations were capable of accurately capturing such flows for complex vane packs. Additionally, structural and modal analyses were conducted using finite element models to determine the correlations between dominant structural modes and dominant wake (flow) modes. The simulations predicted that vortex shedding modes generally contained frequencies 300% larger than dominant structural modes, and therefore, vortex induced vibrations were unlikely to occur. Lastly, mode decomposition methods were applied to the experimental results to extract energy ratios and reveal dynamic content across high-order wake modes. The vortex shedding modes generated more than 80% of the total wake energy for both complex vane packs, and dynamic decomposition methods revealed unique structures within the vane junction wake. In all analyses, comparisons were made between different vane parameters, such as trailing edge thickness and turning angle, where it was found that trailing edge thickness was the dominant vortex shedding parameter. The motivation, methodology, and results of the following research is presented to better understand the wake interactions, computational predictive capabilities, and structural dynamics associated with vortex shedding from complex vane packs. Although the results directly relate to StreamVane distortion generator technology, the qualitative and quantitative comparisons between the selected methods, geometry parameters, and flow conditions can be extrapolated to modern turbomachinery components in general. Therefore, this dissertation aims to benefit distortion generator and turbomachinery designers by providing insight into the underlying physics and overall modeling techniques of the wake dynamics in highly three-dimensional, complex components. / Doctor of Philosophy / A comprehensive analysis has been completed to characterize the unsteady wake flow produced by complex turning vane systems in three dimensions. Turning vanes are a common component utilized in the field of fluid dynamics and aerospace propulsion to effectively turn and manipulate the working fluid to the desired condition. For propulsion applications, similar vanes can alleviate performance losses by improving the overall aerodynamics and mitigating flow distortions entering the compressor of a jet engine. Conversely, complex turning vanes can also be used to reproduce the distortion for engineers to evaluate jet engine components when subjected to nonuniform flow ingestion. The distinct geometry features that make these vanes complex are also present in other turbomachinery systems outside of distortion generation. In any case, the cross-sectional profiles of the turning vanes commonly contain blunt ends or trailing edges due to engineering limitations and/or restrictions. This geometric feature introduces periodic wake structures, known as vortex shedding, that can negatively effect the performance of the overall system. It is therefore a necessity to characterize both the dynamics and coherence of vortex shedding to fully understand the flow features in highly three-dimensional flows. In the presented research, this is achieved by applying computational simulations and experimental measurements to extract the corresponding wake dynamics of complex vane packs. The selected testcases where designed using the StreamVane technology, a mature system that generates tailored turning vanes to reproduce flow distortion in jet engine or fan rig ground-testing facilities. The fluid simulations captured the expected wake flow and largescale structures convecting downstream of the vane packs. A comparison between two different flow models and the experimental results revealed minimal quantitative differences in the large-scale dynamics, which gave insight into the model selection to predict such flows. Additional structural simulations were performed to estimate the forcing and response of the vane packs when subjected to the aerodynamic loading. The results showed vortex shedding was highly unlikely to cause large amplitude vibrations and structural failures. In all analyses, the primary results were correlated with common vane parameters and operating conditions to evaluate their impact on the wake dynamics. The motivation, methodology, and results of the following research is presented to better understand the wake interactions, computational predictive capabilities, and structural dynamics associated with vortex shedding from complex vane packs. Although the results directly relate to StreamVane distortion generator technology, the qualitative and quantitative comparisons between the selected methods, geometry parameters, and flow conditions can be extrapolated to modern turbomachinery components in general. Therefore, this dissertation aims to benefit distortion generator and turbomachinery designers by providing insight into the underlying physics and overall modeling techniques of the wake dynamics in highly three-dimensional, complex components.

Nesta tese foi estudado o transporte de partículas na borda do plasma confinado magneticamente em tokamaks a partir de um modelo para ondas de deriva proveniente de flutuaçõoes eletrostáticas geradas pela não uniformidade do plasma. Para investigar esse problema, consideramos o modelo com duas ondas de deriva, que possui uma complexa dinâmica não linear onde podemos encontrar tanto transporte anômalo quanto transporte difusivo. Para a encontras no plano de fases as Estruturas Lagrangianas Coerentes (ELCs) e os jatos, foram confeccionados mapas de Poincaré, diagramas de expoente de Lyapunov a tempo finito, diagramas de deslocamento quadrático, diagramas de autocorrelação da velocidade e o diagrama de retorno. Para avaliar o impacto dessas ELCs no transporte de partículas foram analisados a série temporal do desvio padrão médio, da dispersão relativa e dos saltos dentro do mapa de Poincar´e e também foram confeccionados histogramas com a distribuição desses saltos. Foi encontrado que, com duas ondas de deriva e para uma determinada combinação de parâmetros, surgem correntes de jato, que persistem por longos períodos, imersas na região caótica. Verificamos que, assim como nas ilhas, a região interna às correntes de jato são inacessíveis às ELCs. Também foi encontrado que, quando existe uma corrente de jato, o transporte observado na região caótica não é simétrico com uma pequena deriva na direção contraria ao jato. Esse fenômeno observado ocorre em contrapartida ao caso típico de sistemas com mistura em que as ELCs tem acesso a todo o plano de fase e o transporte é difusivo. / In this thesis we studied the particle transport in the edge of magnetically confined plasma in tokamaks using a model of drift waves due to electrostatic fluctuations generated by the non-uniformity of the plasma. To investigate this issue, we consider the model with two drift waves, which has a complex nonlinear dynamics where we can find both anomalous and diffusive transport. To find the Lagrangian Coherent Structures (LCSs) and the jets, we used Poincaré maps, Finite time Lyapunov exponent diagrams, quadratic displacement diagrams, autocorrelation velocity diagrams and return displacement diagram. To evaluate the impact of LCSs in the transport of particles, we analyzed the time series of both average standard deviation and relative dispertion and also histograms of the distribution of these jumps. It was found that, with two drift waves and for a given combination of parameters, a jet streams appear in the phase space and persist for long periods of time immersed in the chaotic region. We found that, as well as on the islands, the inner region of the jet streams are inaccessible to LCSs. It was also found that when there is a jet stream, the transport observed in the chaotic region is not symmetrical and have a small drift in the opposite direction to the jet. This phenomenon is observed in contrast to the typical case of systems with mixing in wich the LCSs have access to all the phase space and the trasnport is diffusive.

The Lagrangian dynamics of two-dimensional incompressible fluid flows is considered, with emphasis on transport processes in atmospheric and oceanic flows. The dynamical-systems-based approach is adopted; the Lagrangian motion in such systems is studied with the aid of Kolmogorov-Arnold-Moser (KAM) theory, and results relating to stable and unstable manifolds and lobe dynamics. Some nontrivial extensions of well-known results are discussed, and some extensions of the theory are developed. In problems for which the flow field consists of a steady background on which a time-dependent perturbation is superimposed, it is shown that transport barriers arise naturally and play a critical role in transport processes. Theoretical results are applied to the study of transport in measured and simulated oceanographic and atmospheric flows. Two particular problems are considered. First, we study the Lagrangian dynamics of the zonal jet at the perimeter of the Antarctic Stratospheric Polar Vortex during late winter/early spring within which lies the "ozone hole". In this system, a robust transport barrier is found near the core of a zonal jet under typical conditions, which is responsible for trapping of the ozone-depleted air within the ozone hole. The existence of such a barrier is predicted theoretically and tested numerically with use of a dynamically-motivated analytically-prescribed model. The second, oceanographic, application considered is the study of the surface transport in the Adriatic Sea. The surface flow in the Adriatic is characterized by a robust threegyre background circulation pattern. Motivated by this observation, the Lagrangian dynamics of a perturbed three-gyre system is studied, with emphasis on intergyre transport and the role of transport barriers. It is shown that a qualitative change in transport properties, accompanied by a qualitative change in the structure of stable and unstable manifolds occurs in the perturbed three-gyre system when the perturbation strength exceeds a certain threshold. This behavior is predicted theoretically, simulated numerically with use of an analytically prescribed model, and shown to be consistent with a fully observationally-based model.

Fluid dynamics considers the physics of liquids and gases. This is a branch of classical physics and is totally based on Newton's laws of motion. Nevertheless, the equation of fluid motion, Navier-Stokes equation, becomes very complicated to solve even for very simple configurations. This thesis treats mainly analytical vortex solutions to Navier-Stokes equations. Vorticity is usually concentrated to smaller regions of the flow, sometimes isolated objects, called vortices. If one are able to describe vortex structures exactly, important information about the flow properties are obtained. Initially, the modeling of a conical vortex geometry is considered. The results are compared with wind-tunnel measurements, which have been analyzed in detail. The conical vortex is a very interesting phenomenaon for building engineers because it is responsible for very low pressures on buildings with flat roofs. Secondly, a suggested analytical solution to Navier-Stokes equation for internal flows is presented. This is based on physical argumentation concerning the vorticity production at solid boundaries. Also, to obtain the desired result, Navier-Stokes equation is reformulated and integrated. In addition, a model for required information of vorticity production at boundaries is proposed. The last part of the thesis concerns the examples of vortex models in 2-D and 3-D. In both cases, analysis of the Navier-Stokes equation, leads to the opportunity to construct linear solutions. The 2-D studies are, by the use of diffusive elementary vortices, describing experimentally observed vortex statistics and turbulent energy spectrums in stratified systems and in soapfilms. Finally, in the 3-D analysis, three examples of recent experimentally observed vortex objects are reproduced theoretically. First, coherent structures in a pipe flow is modeled. These vortex structures in the pipe are of interest since they appear for Re in the range where transition to turbulence is expected. The second example considers the motion in a viscous vortex ring. The model, with diffusive properties, describes the experimentally measured velocity field as well as the turbulent energy spectrum. Finally, a streched spiral vortex is analysed. A rather general vortex model that has many degrees of freedom is proposed, which also may be applied in other configurations.

<p>Large-scale coherent structures are systematically investigated in terms of their geometric attributes, importance toward describing turbulent exchange of energy, momentum and mass as well as their relationship to landscape features in the context of land-atmosphere interaction. In the first chapter, we present the motivation of this work as well as a background review of large-scale coherent structures in land-atmosphere interaction. In the second chapter, the methodology of large-eddy simulation (LES) and the proper orthogonal decomposition (POD) is introduced. LES was used to serve as a virtual laboratory to simulate typical scenarios in land-atmosphere interaction and the POD was used as the major technique to educe the coherent structures from turbulent flows in land-atmosphere interaction. In the third chapter, we justify the use of the LES to simulate the realistic coherent structures in the atmospheric boundary layer (ABL) by comparing results obtained from LES of the ABL and direct numerical simulation (DNS) of channel flow. In the fourth chapter, we investigate the effects of a wide range of vegetation density on the coherent structures within the air space within and just above the canopy (the so-called canopy sublayer, CSL). The fifth chapter presents an analysis of the coherent structures across a periodic forest-clearing-forest transition in the steamwise direction. The sixth chapter focuses on the role of coherent structures in explaining scalar dissimilarity in the CSL. The seventh chapter summarizes this dissertation and provides suggestions for future study.</p> / Dissertation

No description available.

abstract: The evolution of single hairpin vortices and multiple interacting hairpin vortices are studied in direct numerical simulations of channel flow at Re-tau=395. The purpose of this study is to observe the effects of increased Reynolds number and varying initial conditions on the growth of hairpins and the conditions under which single hairpins autogenerate hairpin packets. The hairpin vortices are believed to provide a unified picture of wall turbulence and play an important role in the production of Reynolds shear stress which is directly related to turbulent drag. The structures of the initial three-dimensional vortices are extracted from the two-point spatial correlation of the fully turbulent direct numerical simulation of the velocity field by linear stochastic estimation and embedded in a mean flow having the profile of the fully turbulent flow. The Reynolds number of the present simulation is more than twice that of the Re-tau=180 flow from earlier literature and the conditional events used to define the stochastically estimated single vortex initial conditions include a number of new types of events such as quasi-streamwise vorticity and Q4 events. The effects of parameters like strength, asymmetry and position are evaluated and compared with existing results in the literature. This study then attempts to answer questions concerning how vortex mergers produce larger scale structures, a process that may contribute to the growth of length scale with increasing distance from the wall in turbulent wall flows. Multiple vortex interactions are studied in detail. / Dissertation/Thesis / M.S. Mechanical Engineering 2011

abstract: The tools developed for the use of investigating dynamical systems have provided critical understanding to a wide range of physical phenomena. Here these tools are used to gain further insight into scalar transport, and how it is affected by mixing. The aim of this research is to investigate the efficiency of several different partitioning methods which demarcate flow fields into dynamically distinct regions, and the correlation of finite-time statistics from the advection-diffusion equation to these regions. For autonomous systems, invariant manifold theory can be used to separate the system into dynamically distinct regions. Despite there being no equivalent method for nonautonomous systems, a similar analysis can be done. Systems with general time dependencies must resort to using finite-time transport barriers for partitioning; these barriers are the edges of Lagrangian coherent structures (LCS), the analog to the stable and unstable manifolds of invariant manifold theory. Using the coherent structures of a flow to analyze the statistics of trapping, flight, and residence times, the signature of anomalous diffusion are obtained. This research also investigates the use of linear models for approximating the elements of the covariance matrix of nonlinear flows, and then applying the covariance matrix approximation over coherent regions. The first and second-order moments can be used to fully describe an ensemble evolution in linear systems, however there is no direct method for nonlinear systems. The problem is only compounded by the fact that the moments for nonlinear flows typically don't have analytic representations, therefore direct numerical simulations would be needed to obtain the moments throughout the domain. To circumvent these many computations, the nonlinear system is approximated as many linear systems for which analytic expressions for the moments exist. The parameters introduced in the linear models are obtained locally from the nonlinear deformation tensor. / Dissertation/Thesis / Doctoral Dissertation Applied Mathematics 2018

Nesta tese foi estudado o transporte de partículas na borda do plasma confinado magneticamente em tokamaks a partir de um modelo para ondas de deriva proveniente de flutuaçõoes eletrostáticas geradas pela não uniformidade do plasma. Para investigar esse problema, consideramos o modelo com duas ondas de deriva, que possui uma complexa dinâmica não linear onde podemos encontrar tanto transporte anômalo quanto transporte difusivo. Para a encontras no plano de fases as Estruturas Lagrangianas Coerentes (ELCs) e os jatos, foram confeccionados mapas de Poincaré, diagramas de expoente de Lyapunov a tempo finito, diagramas de deslocamento quadrático, diagramas de autocorrelação da velocidade e o diagrama de retorno. Para avaliar o impacto dessas ELCs no transporte de partículas foram analisados a série temporal do desvio padrão médio, da dispersão relativa e dos saltos dentro do mapa de Poincar´e e também foram confeccionados histogramas com a distribuição desses saltos. Foi encontrado que, com duas ondas de deriva e para uma determinada combinação de parâmetros, surgem correntes de jato, que persistem por longos períodos, imersas na região caótica. Verificamos que, assim como nas ilhas, a região interna às correntes de jato são inacessíveis às ELCs. Também foi encontrado que, quando existe uma corrente de jato, o transporte observado na região caótica não é simétrico com uma pequena deriva na direção contraria ao jato. Esse fenômeno observado ocorre em contrapartida ao caso típico de sistemas com mistura em que as ELCs tem acesso a todo o plano de fase e o transporte é difusivo. / In this thesis we studied the particle transport in the edge of magnetically confined plasma in tokamaks using a model of drift waves due to electrostatic fluctuations generated by the non-uniformity of the plasma. To investigate this issue, we consider the model with two drift waves, which has a complex nonlinear dynamics where we can find both anomalous and diffusive transport. To find the Lagrangian Coherent Structures (LCSs) and the jets, we used Poincaré maps, Finite time Lyapunov exponent diagrams, quadratic displacement diagrams, autocorrelation velocity diagrams and return displacement diagram. To evaluate the impact of LCSs in the transport of particles, we analyzed the time series of both average standard deviation and relative dispertion and also histograms of the distribution of these jumps. It was found that, with two drift waves and for a given combination of parameters, a jet streams appear in the phase space and persist for long periods of time immersed in the chaotic region. We found that, as well as on the islands, the inner region of the jet streams are inaccessible to LCSs. It was also found that when there is a jet stream, the transport observed in the chaotic region is not symmetrical and have a small drift in the opposite direction to the jet. This phenomenon is observed in contrast to the typical case of systems with mixing in wich the LCSs have access to all the phase space and the trasnport is diffusive.