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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: 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: Zhengkai He
Publisher:
ISBN:
Category : Aerofoils
Languages : en
Pages : 70
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Book Description
With the inspiration of owl's silent flight, a traditional airfoil S833 equipped with flexible fringes on the trailing edge is investigated through numerical simulation and experiments in a wind tunnel. The newly constructed airfoil is modeled and numerically investigated. An incompressible, 2D and viscous flow solver in the Computational Fluid Dynamics (CFD) software FLUENT is utilized to conduct the numerical simulation on the vortex flow feature in the wake of the airfoil. A User Defined Function code was applied to generate the defined motion of flexible fringes. The effects of the flapping frequency of the fringe and the deformation pattern of the fringe are investigated in the parametric study. On the other hand, the airfoil model with the flexible fringe is manufactured for the experimental study. A digital Particle Image Velocimetry (PIV) system is employed to investigate the flow structure in the wake and the deformation of the flexible fringes. The motion of the trailing edge fringes is extracted from the experimental measurements as the input for CFD simulation. It has been found that the addition of the flexible fringe has a significant effect on the flow characteristics in the vortex wake downstream of the airfoil as well as the aerodynamic performance of the airfoil.
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: Deems Shelton Emmer
Publisher:
ISBN:
Category : Aerofoils
Languages : en
Pages : 412
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Book Description
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: Jean Helder Marques Ribeiro
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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Book Description
External flows over wings is a traditional flow of interest in aerodynamics. Over the last century, research efforts were dedicated to studying the wake patterns that form in the flows around finite wings. Among others, we can pinpoint the wing tip vortex, the separation region that develops under adverse pressure gradient, and the coherent vortical structures. Thanks to these past efforts, we were able to significantly extend our knowledge in aerodynamics, which paved the way for an impressive evolution of aircraft designs in the last century. Over the years, commercial flight became an ordinary asset in our society. More recently, small and micro air vehicles have also reached the market, being operated by individuals who hold no necessary knowledge of the complexity of the Navier-Stokes equations. The advanced knowledge currently held on flight physics has played a fundamental role in the development of aircraft designs, however, there is still room for improvement. In post-stall flow conditions, the aerodynamic performance of the wing decays considerably, making it challenging to sustain flight at high incidence angles. To enable flight in such flow conditions, it is important to develop physics-based flow control strategies capable of improving the overall aerodynamic performance of the wing and its flight stability. The main implications are reduced fuel (and energy) consumption during flight, increased aircraft range, improvements in safety and productivity of air travel, attenuation of the acoustic signature, as well as enabled capability of aircraft to fly in challenging external environments. Towards this goal, many studies have been performed to analyze and control flows over airfoils in spanwise periodic configurations. These may also be called infinite-span wings. These studies were fundamental to revealing important aspects of flow physics. However, in reality, the flows around wings are three-dimensional (3-D). In addition, modern aircraft wings are usually tapered and swept. The 3-D vortex dynamics of flows over wings has a significant influence on aircraft design, by reducing the overall lift, generating induced drag, and increasing flow unsteadiness. Thus, it is important to develop strategies to control the vortex dynamics that encompass the knowledge of the 3-D characteristics of the flow over finite, swept, and tapered wings. Especially for post-stall flow conditions, the wake dynamics around tapered swept wings is largely unexplored. It is still a challenge to understand how the wing geometry relates to the vortex formation for different aspect and taper ratios, as well as angles of attack and sweep. To design control strategies to improve aerodynamic performance for finite, swept, and tapered wings, we must go beyond the sole characterization of flow structures. In fact, the identification of perturbation dynamics is called for to modify the flow field. Three-dimensional flow control is challenging due to the high-dimensional and nonlinear nature of the flow dynamics of the wakes. Thus, it is necessary to find an appropriate actuation setup for the problem that can alter the base flow behavior. This effort can be guided by modal analysis methods. In our work, we have used resolvent analysis, a method based on the singular value decomposition (SVD) of the resolvent, which is a linear operator constructed using the Navier-Stokes equations linearized with respect to the base flow. For unsteady flows, the statistically converged time-averaged flow field is used as a base flow to construct the resolvent operator. The strength of the resolvent operator through this approach is the capability to find optimal forcing modes which amplify outputs in the flow field and give insights into the perturbed flow through the spatial response modes. The challenge within resolvent analysis is the SVD computation for large-scale resolvent operators that are generated for high-dimensional flow fields, such as three-dimensional and turbulent flows. By taking advantage of low-rank approximation of the resolvent operator, recent developments using randomized numerical linear algebra have accelerated the computation of the dominant resolvent modes. With reduced computational costs, these efforts have enabled the use of resolvent analysis in turbulent flows over spanwise periodic airfoils and expanded its applicability to triglobal problems and higher Reynolds number flows. With the randomized algorithm, we can use resolvent analysis to uncover the dynamics of 3-D flows over finite, swept, and tapered wings, supporting flow control efforts to improve their overall aerodynamic performance. The present study has shown how to develop a 3-D resolvent-based flow control over finite wings. We initiate by studying flows over finite wings and the effects of wing sweep and taper on the post-stall wake dynamics through direct numerical simulations (DNS). We consider laminar flows at chord-based Reynolds numbers of 400 and 600 with weak compressible effects at a freestream Mach number 0.1. The flows are studied around wings at angles of attack between 14 and 30 degrees with semi aspect ratios ranging from 1 to 4, sweep angles up to 50 degrees, and taper ratios from 0.27 to 1. Following a comprehensive characterization of the wake dynamics through DNS results, we extend our knowledge of the dynamics of flow perturbations by analyzing the triglobal resolvent modes. Through the identification of the optimal harmonic perturbations that can be amplified in the flow field, we develop 3-D active flow control that is shown to significantly modify the wake structures around the wings. This comprehensive investigation provides novel and unique insights that reveal the flow structures that can be amplified in the wake and modify their dynamics in post-stall flow conditions.
Author: Bernhard Stoevesandt
Publisher: Springer Nature
ISBN: 3030313077
Category : Technology & Engineering
Languages : en
Pages : 1495
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Book Description
This handbook provides both a comprehensive overview and deep insights on the state-of-the-art methods used in wind turbine aerodynamics, as well as their advantages and limits. The focus of this work is specifically on wind turbines, where the aerodynamics are different from that of other fields due to the turbulent wind fields they face and the resultant differences in structural requirements. It gives a complete picture of research in the field, taking into account the different approaches which are applied. This book would be useful to professionals, academics, researchers and students working in the field.
Author: M. Chandrasekhara
Publisher:
ISBN:
Category :
Languages : en
Pages :
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