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Author: Christopher E. Mertes
Publisher:
ISBN: 9781267424235
Category : Aerofoils
Languages : en
Pages : 87
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Book Description
An experimental study was conducted to characterize the effects of pitching motion on vortex shedding behavior in the wake of a flatback airfoil. Experiments were conducted on a static, rigidly mounted airfoil as well as an oscillating airfoil in a wind tunnel facility at the University of Wyoming. Particle image velocimetry was used in conjunction with proper orthogonal decomposition to show that the vortex shedding does behave differently depending on the dynamic configuration of the airfoil. The results show that fundamental vortex shedding from the blunt trailing edge is present in both the static and dynamic case whenever the flow is attached. In a case where the flow separates under dynamic stall conditions, the flow physics are dominated by the dynamic pitching motion, and trailing edge vortex shedding is only present during the attached portion of the pitching cycle. In another case, it was shown that the organization of the vortex shedding changes depending on the point in the oscillation cycle. This dynamic behavior has an impact on the aerodynamic characteristics of the blade.An experimental study was conducted to characterize the effects of pitching motion on vortex shedding behavior in the wake of a flatback airfoil. Experiments were conducted on a static, rigidly mounted airfoil as well as an oscillating airfoil in a wind tunnel facility at the University of Wyoming. Particle image velocimetry was used in conjunction with proper orthogonal decomposition to show that the vortex shedding does behave differently depending on the dynamic configuration of the airfoil. The results show that fundamental vortex shedding from the blunt trailing edge is present in both the static and dynamic case whenever the flow is attached. In a case where the flow separates under dynamic stall conditions, the flow physics are dominated by the dynamic pitching motion, and trailing edge vortex shedding is only present during the attached portion of the pitching cycle. In another case, it was shown that the organization of the vortex shedding changes depending on the point in the oscillation cycle. This dynamic behavior has an impact on the aerodynamic characteristics of the blade.
Author: Christopher E. Mertes
Publisher:
ISBN: 9781267424235
Category : Aerofoils
Languages : en
Pages : 87
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Book Description
An experimental study was conducted to characterize the effects of pitching motion on vortex shedding behavior in the wake of a flatback airfoil. Experiments were conducted on a static, rigidly mounted airfoil as well as an oscillating airfoil in a wind tunnel facility at the University of Wyoming. Particle image velocimetry was used in conjunction with proper orthogonal decomposition to show that the vortex shedding does behave differently depending on the dynamic configuration of the airfoil. The results show that fundamental vortex shedding from the blunt trailing edge is present in both the static and dynamic case whenever the flow is attached. In a case where the flow separates under dynamic stall conditions, the flow physics are dominated by the dynamic pitching motion, and trailing edge vortex shedding is only present during the attached portion of the pitching cycle. In another case, it was shown that the organization of the vortex shedding changes depending on the point in the oscillation cycle. This dynamic behavior has an impact on the aerodynamic characteristics of the blade.An experimental study was conducted to characterize the effects of pitching motion on vortex shedding behavior in the wake of a flatback airfoil. Experiments were conducted on a static, rigidly mounted airfoil as well as an oscillating airfoil in a wind tunnel facility at the University of Wyoming. Particle image velocimetry was used in conjunction with proper orthogonal decomposition to show that the vortex shedding does behave differently depending on the dynamic configuration of the airfoil. The results show that fundamental vortex shedding from the blunt trailing edge is present in both the static and dynamic case whenever the flow is attached. In a case where the flow separates under dynamic stall conditions, the flow physics are dominated by the dynamic pitching motion, and trailing edge vortex shedding is only present during the attached portion of the pitching cycle. In another case, it was shown that the organization of the vortex shedding changes depending on the point in the oscillation cycle. This dynamic behavior has an impact on the aerodynamic characteristics of the blade.
Author: Deems Shelton Emmer
Publisher:
ISBN:
Category : Aerofoils
Languages : en
Pages : 412
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Book Description
Author: Anurag Gandhi
Publisher:
ISBN:
Category : Aerofoils
Languages : en
Pages : 0
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Book Description
The effect of reduced frequency on dynamic stall behavior of a pitching NACA0012 airfoil in a turbulent wake using Direct Numerical Simulations is presented in the current study. Upstream turbulence with dynamically oscillating blades and airfoils is associated with ambient flow unsteadiness and is encountered in many operating conditions. Wake turbulence, a more realistic scenario for airfoils in operation, is generated using a small solid cylinder placed upstream, the vortices shed from which interact with the pitching airfoil affecting dynamic stall behavior. A recently developed moving overlapping grid approach is used using a high-order Spectral Element Method (SEM) for spatial discretization combined with a dynamic time-stepping procedure allowing for up to third order temporal discretization. Two cases of reduced frequency (k = 0:16 and 0:25) for airfoil oscillation are investigated and the change in dynamic stall behavior with change in reduced frequency is studied and documented using flow-fields and aerodynamic coefficients (Drag, Lift and Pitching Moment) with a focus on understanding vortex system dynamics (including formation of secondary vortices) for different reduced frequencies and it's affect on airfoil aerodynamic characteristics and fatigue life. Transition of the flow over the surface of an airfoil for both undisturbed and disturbed flow cases will also be discussed using Pressure coefficient and Skin Friction coefficient data for a given cycle combined with a wavelet analysis using Morse wavelets in MATLAB.
Author: Xiaomin Chen (Mechanical engineer)
Publisher:
ISBN:
Category : Electronic dissertations
Languages : en
Pages : 164
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Book Description
Shape optimization is widely used in the design of wind turbine blades. In this dissertation, a numerical optimization method called Genetic Algorithm (GA) is applied to address the shape optimization of wind turbine airfoils and blades. In recent years, the airfoil sections with blunt trailing edge (called flatback airfoils) have been proposed for the inboard regions of large wind-turbine blades because they provide several structural and aerodynamic performance advantages. The FX, DU and NACA 64 series airfoils are thick airfoils widely used for wind turbine blade application. They have several advantages in meeting the intrinsic requirements for wind turbines in terms of design point, off-design capabilities and structural properties. This research employ both single- and multi-objective genetic algorithms (SOGA and MOGA) for shape optimization of Flatback, FX, DU and NACA 64 series airfoils to achieve maximum lift and/or maximum lift to drag ratio. The commercially available software FLUENT is employed for calculation of the flow field using the Reynolds-Averaged Navier-Stokes (RANS) equations in conjunction with a two-equation Shear Stress Transport (SST) turbulence model and a three equation k-kl-[omega] turbulence model. The optimization methodology is validated by an optimization study of subsonic and transonic airfoils (NACA0012 and RAE 2822 airfoils). All the optimization results have demonstrated that the GA technique can be employed efficiently and accurately to produce globally optimal airfoils with excellent aerodynamic properties using a desired objective value (minimum Cd and/or maximum Cl /Cd). It is also shown that the multi-objective genetic algorithm based optimization can generate superior airfoils compared to those obtained by using the single objective genetic algorithm. The applications of thick airfoils are extended to the assessment of wind turbine performance. It is well established that the power generated by a Horizontal-Axis Wind Turbine (HAWT) is a function of the number of blades B, the tip speed ratio [lambda] (blade tip speed/wind free stream velocity) and the lift to drag ratio (Cl /Cd) of the airfoil sections of the blade. The airfoil sections used in HAWT are generally thick airfoils such as the S, DU, FX, Flat-back and NACA 6-series of airfoils. These airfoils vary in (Cl /Cd) for a given B and [lambda], and therefore the power generated by HAWT for different blade airfoil sections will vary. Another goal of this study is to evaluate the effect of different airfoil sections on HAWT performance using the Blade Element Momentum (BEM) theory. In this dissertation, we employ DU 91-W2-250, FX 66-S196-V1, NACA 64421, and Flat-back series of airfoils (FB-3500-0050, FB-3500-0875, and FB-3500-1750) and compare their performance with S809 airfoil used in NREL Phase II and III wind turbines; the lift and drag coefficient data for these airfoils sections are available. The output power of the turbine is calculated using these airfoil section blades for a given B and [lambda] and is compared with the original NREL Phase II and Phase III turbines using S809 airfoil section. It is shown that by a suitable choice of airfoil section of HAWT blade, the power generated by the turbine can be significantly increased. Parametric studies are also conducted by varying the turbine diameter. In addition, a simplified dynamic inflow model is integrated into the BEM theory. It is shown that the improved BEM theory has superior performance in capturing the instantaneous behavior of wind turbines due to the existence of wind turbine wake or temporal variations in wind velocity. The dissertation also considers the Wind Farm layout optimization problem using a genetic algorithm. Both the Horizontal -Axis Wind Turbines (HAWT) and Vertical-Axis Wind Turbines (VAWT) are considered. The goal of the optimization problem is to optimally position the turbines within the wind farm such that the wake effects are minimized and the power production is maximized. The reasonably accurate modeling of the turbine wake is critical in determination of the optimal layout of the turbines and the power generated. For HAWT, two wake models are considered; both are found to give similar answers. For VAWT, a very simple wake model is employed. Finally, some preliminary investigation of shape optimization of 3D wind turbine blades at low Reynolds numbers is conducted. The optimization employs a 3D straight untapered wind turbine blade with cross section of NACA 0012 airfoils as the geometry of baseline blade. The optimization objective is to achieve maximum Cl /Cd as well as maximum Cl. The multi-objective genetic algorithm is employed together with the commercially available software FLUENT for calculation of the flow field using the Reynolds-Averaged Navier-Stokes (RANS) equations in conjunction with a one-equation Sparlart-Allmaras turbulence model. The results show excellent performance of the optimized wind turbine blade and indicate the feasibility of optimization on real wind turbine blades with more complex shapes in the future.
Author: M. Chandrasekhara
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
Author:
Publisher:
ISBN:
Category : Printed ephemera
Languages : en
Pages :
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Book Description
The ephemera collection contains documents of everyday life generally covering publications of fewer than five pages. These may include: advertising material, area guides, booklets, brochures, samples of merchandise postcards, posters, programs, stickers and tickets.
Author: K. W. Tupper
Publisher:
ISBN:
Category :
Languages : en
Pages : 81
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Book Description
The purpose of this study was to investigate the effect a trailing vortex wake has on an airfoil undergoing a constant rate of change of angle of attack, alpha, in two-dimensional, incompressible, irrotational flow. Potential flow theory, conformal mapping by the Joukowski transformation, and numerical integration and differentiation techniques were used to develop a computer algorithm to model the problem. Once the program was formulated, it was used to solve the impulsive-start problem of airfoil motion. The results were found to be in excellent agreement with the results obtained by others. When applied to the constant rate-of-change of angle-of-attack problem, the results showed that a trailing vortex wake has a measurable and predictable effect on the production of lift on an airfoil undergoing a constant alpha. While results of this work, taken alone, are helpful in understanding the phenomena known as dynamic stall, coupled with existing boundary-layer studies the results may lead to additional understanding of the phenomena. More specifically, the computer program develop here could be used to predict more realistically the inviscid flow about a pitching airfoil as it approaches the dynamic-stall conditions.
Author: Galih Bangga
Publisher: kassel university press GmbH
ISBN: 373760536X
Category :
Languages : en
Pages : 183
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Book Description
This book presents the state of the art in the analyses of three-dimensional flow over rotating wind turbine blades. Systematic studies for wind turbine rotors with different sizes were carried out numerically employing three different simulation approaches, namely the Euler, URANS and DDES methods. The main mechanisms of the lift augmentation in the blade inboard region are described in detail. The physical relations between the inviscid and viscous effects are presented and evaluated, emphasizing the influence of the flow curvature on the resulting pressure distributions. Detailed studies concerning the lift augmentation for large wind turbine rotors are considered as thick inboard airfoils characterized by massive separation are desired to stronger contribute to power production. Special attention is given to the analyses of wind turbine loads and flow field that can be helpful for the interpretation of the occurring physical phenomena. The book is aimed at students, researchers, engineers and physicists dealing with wind engineering problems, but also for a wider audience involved in flow computations.
Author: Jewel B. Barlow
Publisher: John Wiley & Sons
ISBN: 0471557749
Category : Technology & Engineering
Languages : en
Pages : 738
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Book Description
A brand-new edition of the classic guide on low-speed wind tunnel testing While great advances in theoretical and computational methods have been made in recent years, low-speed wind tunnel testing remains essential for obtaining the full range of data needed to guide detailed design decisions for many practical engineering problems. This long-awaited Third Edition of William H. Rae, Jr.'s landmark reference brings together essential information on all aspects of low-speed wind tunnel design, analysis, testing, and instrumentation in one easy-to-use resource. Written by authors who are among the most respected wind tunnel engineers in the world, this edition has been updated to address current topics and applications, and includes coverage of digital electronics, new instrumentation, video and photographic methods, pressure-sensitive paint, and liquid crystal-based measurement methods. The book is organized for quick access to topics of interest, and examines basic test techniques and objectives of modeling and testing aircraft designs in low-speed wind tunnels, as well as applications to fluid motion analysis, automobiles, marine vessels, buildings, bridges, and other structures subject to wind loading. Supplemented with real-world examples throughout, Low-Speed Wind Tunnel Testing, Third Edition is an indispensable resource for aerospace engineering students and professionals, engineers and researchers in the automotive industries, wind tunnel designers, architects, and others who need to get the most from low-speed wind tunnel technology and experiments in their work.
Author: James F. Manwell
Publisher: John Wiley & Sons
ISBN: 9780470686287
Category : Technology & Engineering
Languages : en
Pages : 704
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Book Description
Wind energy’s bestselling textbook- fully revised. This must-have second edition includes up-to-date data, diagrams, illustrations and thorough new material on: the fundamentals of wind turbine aerodynamics; wind turbine testing and modelling; wind turbine design standards; offshore wind energy; special purpose applications, such as energy storage and fuel production. Fifty additional homework problems and a new appendix on data processing make this comprehensive edition perfect for engineering students. This book offers a complete examination of one of the most promising sources of renewable energy and is a great introduction to this cross-disciplinary field for practising engineers. “provides a wealth of information and is an excellent reference book for people interested in the subject of wind energy.” (IEEE Power & Energy Magazine, November/December 2003) “deserves a place in the library of every university and college where renewable energy is taught.” (The International Journal of Electrical Engineering Education, Vol.41, No.2 April 2004) “a very comprehensive and well-organized treatment of the current status of wind power.” (Choice, Vol. 40, No. 4, December 2002)
