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Flow control : theoretical concept of absolute instability

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ISBN: 9783866445314 Year: Pages: 97 p. DOI: 10.5445/KSP/1000016554 Language: ENGLISH
Publisher: KIT Scientific Publishing
Subject: Technology (General)
Added to DOAB on : 2019-07-30 20:01:58
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At the 37th Prandtl memorial lecture on Regions of Viccous Flow, H.Oertel 1994 developed for the first time the stability theory of local perturbations in boundary layers and wake flows, as well as their practical application in the flow control of vehicle flows and the boundary layer of civil aircraft wings.This work presents how the stability theory concept of absolute instability has advanced and proven in practice in the last 15 years in terms of the efficient flow control.

Shallow turbulent wake flows: momentum and mass transfer due to large-scale coherent vortical structures

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Book Series: Dissertationsreihe am Institut für Hydromechanik der Universität Karlsruhe (TH) ISSN: 14394111 ISBN: 3937300635 Year: Volume: 2005,2 Pages: XXVI, 398 p. DOI: 10.5445/KSP/1000003453 Language: ENGLISH
Publisher: KIT Scientific Publishing
Subject: General and Civil Engineering
Added to DOAB on : 2019-07-30 20:01:59
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Shallow turbulent wake flows are generated by large obstacles - like islands or headlands - introduced to shallow turbulent open-channel flows. Large-scale quasi two-dimensional vortices may shed off from an obstacle, and advect downstream in a vertical shear flow with predominantly small-scale turbulence induced by bottom friction. Experimental, analytical, and numerical techniques are employed in the present study to characterize the mean flow and turbulence properties of shallow wakes; mechanisms of generation and decay of large-scale vortical structures are clarified, as is their influence on momentum and mass transport in shallow wakes; the global and local stability of shallow wakes is analyzed and evidenced from experimental data. Part I of this work covers non-intrusive optical measurement techniques especially adapted to investigate shallow shear flows. Flow velocities and mass concentrations are obtained (i) point-wise with high spatiotemporal resolution using a combinded LDV-LIF system, and (ii) field-wise using near-surface PIV and depth-averaged PCA systems with a coupling by phase-resolved averaging. Improved algorithms for the evaluation of mass concentrations are based on hydro-optical models of the underlying fluorescence and light attenuation processes. Part II addresses the time-mean description of shallow wake flows. The stochastic description of the turbulence fields displays a characteristic spectral distribution both of kinetic energy and of mass variance, which is partially consistent with the theory of unbounded 2D turbulence at large scales, and with the theory of homogeneous 3D turbulence at small scales. An integral wake model including the effect of bottom friction is derived analytically, and is validated by experimental data. The time-mean distributions of flow velocities and of mass concentration allow to identify wake near fields and far fields with specific asymptotic wake developments. Wake stability classes are associated with local stability regions suggested by linear stability analyses. Part III elaborates the structure and dynamics of quasi-periodic wake flows and the significance of large-scale eddies. This involves a structure identification scheme to educe individual vortices, and a phase-resolved averaging procedure to decompose the flow fields into large-scale coherent and small-scale turbulent parts. A Numerical Particle Tracking technique is employed to model the mass transport and to elucidate different diffusion and dispersion effects.

Remote Sensing of Atmospheric Conditions for Wind Energy Applications

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ISBN: 9783038979425 / 9783038979432 Year: Pages: 290 DOI: 10.3390/books978-3-03897-943-2 Language: eng
Publisher: MDPI - Multidisciplinary Digital Publishing Institute
Subject: Science (General) --- Physics (General)
Added to DOAB on : 2019-06-26 08:44:06
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This Special Issue “Atmospheric Conditions for Wind Energy Applications” hosts papers on aspects of remote sensing for atmospheric conditions for wind energy applications. Wind lidar technology is presented from a theoretical view on the coherent focused Doppler lidar principles. Furthermore, wind lidar for applied use for wind turbine control, wind farm wake, and gust characterizations is presented, as well as methods to reduce uncertainty when using lidar in complex terrain. Wind lidar observations are used to validate numerical model results. Wind Doppler lidar mounted on aircraft used for observing winds in hurricane conditions and Doppler radar on the ground used for very short-term wind forecasting are presented. For the offshore environment, floating lidar data processing is presented as well as an experiment with wind-profiling lidar on a ferry for model validation. Assessments of wind resources in the coastal zone using wind-profiling lidar and global wind maps using satellite data are presented..

Keywords

detached eddy simulation --- turbulence --- Lidar --- range gate length --- wind energy resources --- QuikSCAT --- WindSAT --- ASCAT --- global ocean --- wind energy --- resource assessment --- power performance testing --- wind turbine controls --- complex flow --- Doppler lidar --- coherent Doppler lidar --- wind sensing --- single-particle --- wind gusts --- Doppler lidar --- detecting and tracking --- impact prediction --- wind energy --- atmospheric boundary layer --- wind turbine wake --- wind lidar --- turbulence --- wake modeling --- field experiments --- wind energy --- atmospheric boundary layer --- wind turbine wake --- wind lidar --- virtual lidar --- turbulence --- wake modeling --- large-eddy simulations --- tropical cyclones --- Doppler Wind Lidar --- atmospheric boundary layer --- wind structure --- wind energy --- Doppler lidar --- wind turbine controls --- lidar-assisted control (LAC) --- IEA Wind Task 32 --- coastal wind measurement --- vertical Light Detection and Ranging --- NeoWins --- fetch effect --- Hazaki Oceanographical Research Station --- empirical equation --- complex terrain --- complex flow --- lidar --- VAD --- remote sensing --- wind energy --- Doppler lidar --- NWP model --- mesoscale --- Floating Lidar System (FLS), wind resource assessment --- wind atlas --- lidar --- wind --- Doppler --- aerosol --- motion estimation --- optical flow --- cross-correlation --- wind energy --- gust prediction --- variational analysis --- Doppler radar --- five-minute ahead wind power forecasting --- probabilistic forecasting --- remote sensing forecasting --- offshore wind speed forecasting --- wind energy --- remote sensing --- Doppler wind lidar --- velocity-azimuth-display algorithm --- resource assessment --- offshore --- turbulence intensity --- Doppler wind lidar --- wind energy --- aerosol --- wind turbine --- wind farm --- wake --- control --- complex terrain --- offshore

Computational Aerodynamic Modeling of Aerospace Vehicles

Authors: ---
ISBN: 9783038976103 Year: Pages: 294 DOI: 10.3390/books978-3-03897-611-0 Language: eng
Publisher: MDPI - Multidisciplinary Digital Publishing Institute
Subject: Technology (General) --- General and Civil Engineering --- Transportation
Added to DOAB on : 2019-03-08 11:42:05
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Currently, the use of computational fluid dynamics (CFD) solutions is considered as the state-of-the-art in the modeling of unsteady nonlinear flow physics and offers an early and improved understanding of air vehicle aerodynamics and stability and control characteristics. This Special Issue covers recent computational efforts on simulation of aerospace vehicles including fighter aircraft, rotorcraft, propeller driven vehicles, unmanned vehicle, projectiles, and air drop configurations. The complex flow physics of these configurations pose significant challenges in CFD modeling. Some of these challenges include prediction of vortical flows and shock waves, rapid maneuvering aircraft with fast moving control surfaces, and interactions between propellers and wing, fluid and structure, boundary layer and shock waves. Additional topic of interest in this Special Issue is the use of CFD tools in aircraft design and flight mechanics. The problem with these applications is the computational cost involved, particularly if this is viewed as a brute-force calculation of vehicle’s aerodynamics through its flight envelope. To make progress in routinely using of CFD in aircraft design, methods based on sampling, model updating and system identification should be considered.

Keywords

wake --- bluff body --- square cylinder --- DDES --- URANS --- turbulence model --- large eddy simulation --- Taylor–Green vortex --- numerical dissipation --- modified equation analysis --- truncation error --- MUSCL --- dynamic Smagorinsky subgrid-scale model --- kinetic energy dissipation --- computational fluid dynamics (CFD) --- microfluidics --- numerical methods --- gasdynamics --- shock-channel --- microelectromechanical systems (MEMS) --- discontinuous Galerkin finite element method (DG–FEM) --- fluid mechanics --- characteristics-based scheme --- multi-directional --- Riemann solver --- Godunov method --- bifurcation --- wind tunnel --- neural networks --- modeling --- unsteady aerodynamic characteristics --- high angles of attack --- hypersonic --- wake --- chemistry --- slender-body --- angle of attack --- detection --- after-body --- S-duct diffuser --- flow distortion --- flow control --- vortex generators --- aeroelasticity --- reduced-order model --- flutter --- wind gust responses --- computational fluid dynamics --- convolution integral --- sharp-edge gust --- reduced order aerodynamic model --- geometry --- meshing --- aerodynamics --- CPACS --- MDO --- VLM --- Euler --- CFD --- variable fidelity --- multi-fidelity --- aerodynamic performance --- formation --- VLM --- RANS --- hybrid reduced-order model --- quasi-analytical --- aeroelasticity --- flexible wings --- subsonic --- wing–propeller aerodynamic interaction --- p-factor --- installed propeller --- overset grid approach

Wind Turbine Aerodynamics

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ISBN: 9783039215249 / 9783039215256 Year: Pages: 410 DOI: 10.3390/books978-3-03921-525-6 Language: eng
Publisher: MDPI - Multidisciplinary Digital Publishing Institute
Subject: Technology (General) --- General and Civil Engineering
Added to DOAB on : 2019-12-09 11:49:15
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Wind turbine aerodynamics is one of the central subjects of wind turbine technology. To reduce the levelized cost of energy (LCOE), the size of a single wind turbine has been increased to 12 MW at present, with further increases expected in the near future. Big wind turbines and their associated wind farms have many advantages but also challenges. The typical effects are mainly related to the increase in Reynolds number and blade flexibility. This Special Issue is a collection of 21 important research works addressing the aerodynamic challenges appearing in such developments. The 21 research papers cover a wide range of problems related to wind turbine aerodynamics, which includes atmospheric turbulent flow modeling, wind turbine flow modeling, wind turbine design, wind turbine control, wind farm flow modeling in complex terrain, wind turbine noise modeling, vertical axis wind turbine, and offshore wind energy. Readers from all over the globe are expected to greatly benefit from this Special Issue collection regarding their own work and the goal of enabling the technological development of new environmentally friendly and cost-effective wind energy systems in order to reach the target of 100% energy use from renewable sources, worldwide, by 2050

Keywords

H-type floating VAWT --- truss Spar floating foundation --- coupling of aerodynamics and hydrodynamics --- computational fluid dynamics --- wind farm --- complex terrain --- SCADA --- met mast measurements --- wind turbine --- simplified free vortex wake --- vortex ring --- aerodynamics --- axial steady condition --- variable pitch --- H-type VAWT --- straight blade --- DMST model --- NACA0012 --- wind energy --- power coefficient --- tip speed ratio --- wind turbine blade optimization --- computational fluid dynamic --- actuator disc --- wake effect --- Non-dominated Sorting Genetic Algorithm (NSGA-II) --- wind turbine airfoil --- dynamic stall --- boundary layer separation --- aerodynamic characteristics --- rotor blade optimization --- blade parametrization --- computational fluid dynamics --- OpenFOAM --- gradient-based --- adjoint approach --- wind turbine optimization --- low wind speed areas --- cost of energy --- particle swarm optimization --- dynamic stall --- pitch oscillation --- oscillating freestream --- rotational augmentation --- wind turbine --- turbulence --- super-statistics --- piezo-electric flow sensor --- ABL stability --- laminar-turbulent transition --- wind speed extrapolation --- atmospheric stability --- wind shear --- wind resource assessment --- wind turbine --- stall --- NREL Phase VI --- S809 airfoil --- MEXICO --- RANS --- wind turbine wakes --- turbulence --- actuator disk --- LES --- wind tunnel --- OpenFOAM --- wind turbine --- wind turbine design --- optimization --- blade length --- economic analysis --- typhoon --- wind turbine --- meso/microscale --- aerodynamic force --- mechanical performance --- thermography --- wind turbine blades --- defects --- image processing --- condition monitoring --- wind farm --- layout optimization --- design --- random search --- complex terrain --- airfoil design --- aerodynamic --- wind tunnel experiment --- VAWTs (Vertical axis wind turbines) --- computational fluid dynamics --- floating offshore wind turbine --- dynamic fluid body interaction --- semi-submersible platform --- OC5 DeepCWind --- wind turbine --- aerodynamics --- turbulent inflow --- Computational Fluid Dynamics --- blade element momentum theory --- actuator line method --- Fatigue Loads --- wind turbine noise source --- wind turbine noise propagation --- wind turbine wake --- n/a

Turbulence in River and Maritime Hydraulics

Authors: --- ---
ISBN: 9783038975946 Year: Pages: 296 DOI: 10.3390/books978-3-03897-595-3 Language: eng
Publisher: MDPI - Multidisciplinary Digital Publishing Institute
Subject: General and Civil Engineering --- Technology (General)
Added to DOAB on : 2019-03-21 15:50:41
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Understanding of the role of turbulence in controlling transport processes is of paramount importance for the preservation and protection of aquatic ecosystems, the minimization of the deleterious consequences of anthropogenic activity, and the successful sustainable development of river and maritime areas. In this context, the present Special Issue collects 15 papers which provide a representation of the present understanding of turbulent processes and their effects in river and maritime environments. The presented collection of papers is not exhaustive, but it highlights the key priority areas and knowledge gaps in this field of research. The published papers present the state-of-the-art knowledge of complex environmental flows which are useful for researchers and practitioners. The paper contents are an overview of some recent topics of research and an exposure of the current and future challenges associated with these topics.

Keywords

breaking waves --- turbulence invariants --- laboratory experiments --- flow-through system --- tidal inlets --- residence time --- coastal lagoon --- MIKE 3 FM (HD & --- TR) --- MIKE 21 FM (HD) --- dense jet --- current flow --- velocity --- trajectory --- turbulence --- dissipation --- rivers --- meanders --- turbulence --- secondary motion --- prediction --- bedrock canyon --- ADCP --- eddy viscosity --- bed shear stress --- spatial analysis --- smoothed particle hydrodynamics models --- physical modelling --- plunging breaking waves --- vorticity --- turbulent jet --- wave–current interaction --- spectral dissipation --- bottom friction --- numerical model --- hydrodynamic model --- spectral model --- wave attenuation --- energy dissipation --- drag coefficient --- flexible vegetation --- Spartina maritima --- vegetation patch --- wake region --- submerged ratio --- SVF --- channel confluences --- junction angle --- flow deflection zone --- flow retardation zone --- flow separation zone --- numerical modelling --- PANORMUS --- jets --- waves --- turbulence --- mixing --- diffusion --- advection --- river mouth --- flow mixing --- nonlinear shallow water equations --- macrovortices --- sub-grid turbulence --- seabed friction --- flow resistance --- roughness --- gravel-bed rivers --- casting technique --- CFD --- Kelvin–Helmholtz --- billow --- lobe --- cleft --- gravity current --- surface waves --- inclined negatively buoyant jets --- regular waves --- dilution --- sea discharges --- rivers --- maritime areas --- turbulent processes

Updates in Pediatric Sleep and Child Psychiatry

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ISBN: 9783038979388 / 9783038979395 Year: Pages: 160 DOI: 10.3390/books978-3-03897-939-5 Language: eng
Publisher: MDPI - Multidisciplinary Digital Publishing Institute
Subject: Medicine (General) --- Pediatrics
Added to DOAB on : 2019-06-26 08:44:06
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Sleep-related symptoms are common in the majority of psychiatric diagnostic categories. The overlap of sleep and psychiatric disorders have been demonstrated in numerous studies. The understanding of sleep and child psychiatry has progressively evolved in the last decade and newer insights have developed regarding the complex interaction between sleep and psychopathology. This collection of articles represents updates on sleep and psychiatric disorders with medical and neurological co-morbidities in children and adolescents.

Intermittency and Self-Organisation in Turbulence and Statistical Mechanics

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ISBN: 9783039211081 / 9783039211098 Year: Pages: 298 DOI: 10.3390/books978-3-03921-109-8 Language: eng
Publisher: MDPI - Multidisciplinary Digital Publishing Institute
Subject: Science (General) --- Mathematics
Added to DOAB on : 2019-08-28 11:21:27
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There is overwhelming evidence, from laboratory experiments, observations, and computational studies, that coherent structures can cause intermittent transport, dramatically enhancing transport. A proper description of this intermittent phenomenon, however, is extremely difficult, requiring a new non-perturbative theory, such as statistical description. Furthermore, multi-scale interactions are responsible for inevitably complex dynamics in strongly non-equilibrium systems, a proper understanding of which remains a main challenge in classical physics. As a remarkable consequence of multi-scale interaction, a quasi-equilibrium state (the so-called self-organisation) can however be maintained. This special issue aims to present different theories of statistical mechanics to understand this challenging multiscale problem in turbulence. The 14 contributions to this Special issue focus on the various aspects of intermittency, coherent structures, self-organisation, bifurcation and nonlocality. Given the ubiquity of turbulence, the contributions cover a broad range of systems covering laboratory fluids (channel flow, the Von Kármán flow), plasmas (magnetic fusion), laser cavity, wind turbine, air flow around a high-speed train, solar wind and industrial application.

Sea Surface Roughness Observed by High Resolution Radar

Authors: --- --- ---
ISBN: 9783039217465 / 9783039217472 Year: Pages: 202 DOI: 10.3390/books978-3-03921-747-2 Language: eng
Publisher: MDPI - Multidisciplinary Digital Publishing Institute
Subject: Science (General) --- Oceanography
Added to DOAB on : 2019-12-09 11:49:16
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Changes in sea surface roughness are usually associated with a change in the sea surface wind field. This interaction has been exploited to measure sea surface wind speed by scatterometry. A number of features on the sea surface associated with changes in roughness can be observed by synthetic aperture radar (SAR) because of the change in Bragg backscatter of the radar signal by damping of the resonant ocean capillary waves. With various radar frequencies, resolutions, and modes of polarization, sea surface features have been analyzed in numerous campaigns, bringing various datasets together, thus allowing for new insights into small-scale processes at a larger areal coverage. This Special Issue aims at investigating sea surface features detected by high spatial resolution radar systems, such as SAR.

Large Grid-Connected Wind Turbines

Authors: ---
ISBN: 9783038977568 Year: Pages: 212 DOI: 10.3390/books978-3-03897-757-5 Language: eng
Publisher: MDPI - Multidisciplinary Digital Publishing Institute
Subject: Physics (General) --- Science (General)
Added to DOAB on : 2019-04-05 10:34:31
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This book covers the technological progress and developments of a large-scale wind energy conversion system along with its future trends, with each chapter constituting a contribution by a different leader in the wind energy arena. Recent developments in wind energy conversion systems, system optimization, stability augmentation, power smoothing, and many other fascinating topics are included in this book. Chapters are supported through modeling, control, and simulation analysis. This book contains both technical and review articles.

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