Download or read book Stochastic Methods for Unsteady Aerodynamic Analysis of Wings and Wind Turbine Blades written by Manuel Fluck and published by . This book was released on 2017 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Advancing towards `better' wind turbine designs engineers face two central challenges: first, current aerodynamic models (based on Blade Element Momentum theory) are inherently limited to comparatively simple designs of flat rotors with straight blades. However, such designs present only a subset of possible designs. Better concepts could be coning rotors, swept or kinked blades, or blade tip modifications. To be able to extend future turbine optimization to these new concepts a different kind of aerodynamic model is needed. Second, it is difficult to include long term loads (life time extreme and fatigue loads) directly into the wind turbine design optimization. This is because with current methods the assessment of long term loads is computationally very expensive -- often too expensive for optimization. This denies the optimizer the possibility to fully explore the effects of design changes on important life time loads, and one might settle with a sub-optimal design. In this dissertation we present work addressing these two challenges, looking at wing aerodynamics in general and focusing on wind turbine loads in particular. We adopt a Lagrangian vortex model to analyze bird wings. Equipped with distinct tip feathers, these wings present very complex lifting surfaces with winglets, stacked in sweep and dihedral. Very good agreement between experimental and numerical results is found, and thus we confirm that a vortex model is actually capable of analyzing complex new wing and rotor blade geometries. Next stochastic methods are derived to deal with the time and space coupled unsteady aerodynamic equations. In contrast to deterministic models, which repeatedly analyze the loads for different input samples to eventually estimate life time load statistics, the new stochastic models provide a continuous process to assess life time loads in a stochastic context -- starting from a stochastic wind field input through to a stochastic solution for the load output. Hence, these new models allow obtaining life time loads much faster than from the deterministic approach, which will eventually make life time loads accessible to a future stochastic wind turbine optimization algorithm. While common stochastic techniques are concerned with random parameters or boundary conditions (constant in time), a stochastic treatment of turbulent wind inflow requires a technique capable to handle a random field. The step from a random parameter to a random field is not trivial, and hence the new stochastic methods are introduced in three stages. First the bird wing model from above is simplified to a one element wing/ blade model, and the previously deterministic solution is substituted with a stochastic solution for a one-point wind speed time series (a random process). Second, the wind inflow is extended to an $n$-point correlated random wind field and the aerodynamic model is extended accordingly. To complete this step a new kind of wind model is introduced, requiring significantly fewer random variables than previous models. Finally, the stochastic method is applied to wind turbine aerodynamics (for now based on Blade Element Momentum theory) to analyze rotor thrust, torque, and power. Throughout all these steps the stochastic results are compared to result statistics obtained via Monte Carlo analysis from unsteady reference models solved in the conventional deterministic framework. Thus it is verified that the stochastic results actually reproduce the deterministic benchmark. Moreover, a considerable speed-up of the calculations is found (for example by a factor 20 for calculating blade thrust load probability distributions). Results from this research provide a means to much more quickly analyze life time loads and an aerodynamic model to be used a new wind turbine optimization framework, capable of analyzing new geometries, and actually optimizing wind turbine blades with life time loads in mind. However, to limit the scope of this work, we only present the aerodynamic models here and will not proceed to turbine optimization itself, which is left for future work.
Download or read book Wind Turbine Aerodynamics and Vorticity Based Methods written by Emmanuel Branlard and published by Springer. This book was released on 2017-04-05 with total page 632 pages. Available in PDF, EPUB and Kindle. Book excerpt: The book introduces the fundamentals of fluid-mechanics, momentum theories, vortex theories and vortex methods necessary for the study of rotors aerodynamics and wind-turbines aerodynamics in particular. Rotor theories are presented in a great level of details at the beginning of the book. These theories include: the blade element theory, the Kutta-Joukowski theory, the momentum theory and the blade element momentum method. A part of the book is dedicated to the description and implementation of vortex methods. The remaining of the book focuses on the study of wind turbine aerodynamics using vortex-theory analyses or vortex-methods. Examples of vortex-theory applications are: optimal rotor design, tip-loss corrections, yaw-models and dynamic inflow models. Historical derivations and recent extensions of the models are presented. The cylindrical vortex model is another example of a simple analytical vortex model presented in this book. This model leads to the development of different BEM models and it is also used to provide the analytical velocity field upstream of a turbine or a wind farm under aligned or yawed conditions. Different applications of numerical vortex methods are presented. Numerical methods are used for instance to investigate the influence of a wind turbine on the incoming turbulence. Sheared inflows and aero-elastic simulations are investigated using vortex methods for the first time. Many analytical flows are derived in details: vortex rings, vortex cylinders, Hill's vortex, vortex blobs etc. They are used throughout the book to devise simple rotor models or to validate the implementation of numerical methods. Several Matlab programs are provided to ease some of the most complex implementations.
Download or read book Aerodynamics of Wind Turbines 2nd edition written by Martin O. L. Hansen and published by Routledge. This book was released on 2013-05-13 with total page 192 pages. Available in PDF, EPUB and Kindle. Book excerpt: Aerodynamics of Wind Turbines is the established essential text for the fundamental solutions to efficient wind turbine design. Now in its second edition, it has been entirely updated and substantially extended to reflect advances in technology, research into rotor aerodynamics and the structural response of the wind turbine structure. Topics covered include increasing mass flow through the turbine, performance at low and high wind speeds, assessment of the extreme conditions under which the turbine will perform and the theory for calculating the lifetime of the turbine. The classical Blade Element Momentum method is also covered, as are eigenmodes and the dynamic behaviour of a turbine. The new material includes a description of the effects of the dynamics and how this can be modelled in an ?aeroelastic code?, which is widely used in the design and verification of modern wind turbines. Further, the description of how to calculate the vibration of the whole construction, as well as the time varying loads, has been substantially updated.
Download or read book Aeroelastic Analysis of a Wind Turbine Blade Using the Harmonic Balance Method written by Jason Charles Howison and published by . This book was released on 2015 with total page 165 pages. Available in PDF, EPUB and Kindle. Book excerpt: Most current wind turbine aeroelastic codes rely on the blade element momentum method with empirical corrections to compute aerodynamic forces on the wind turbine blades. While efficient, this method relies on experimental data and does not allow designers much flexibility for alternative blade designs. Unsteady solutions to the Navier-Stokes equations offer a significant improvement in aerodynamic modeling, but these are currently too computationally expensive to be useful in a design situation. However, steady-state solutions to the Navier-Stokes equations are possible with reasonable computation times. The harmonic balance method provides a way to represent unsteady, periodic flows through coupled a set of steady-state solutions. This method offers the possibility of unsteady flow solutions at a computational cost on the order of a few steady-state solutions. By coupling a harmonic balance driven aerodynamic model with a mode shape-based structural dynamics model, an efficient aeroelastic model for a wind turbine blade driven by the Navier-Stokes equations is developed in this dissertation. For wind turbine flows, turbulence modeling is essential, especially in the transition of the boundary layer from laminar to turbulent. As part of this dissertation, the Spalart-Allmaras turbulence model and the gamma-Re theta-t transition model are included in the aerodynamic model. This marks the first time that this transition model, turbulence model, and the harmonic balance method have been coupled to study unsteady wind turbine aerodynamics. Results show that the transition model matches experimental data more closely than a fully turbulent model for the onset of both static and dynamic stall. Flutter is of particular interest as turbines continue to increase in size, and longer and softer blades continue to enter the field. In this dissertation, flutter is investigated for the 1.5 MW WindPACT rotor blade. The aeroelastic model created, which incorporates the harmonic balance method and a fully turbulent aerodynamic model, is the first of its kind for wind turbine flutter analysis. Predictions match those of other aeroelastic models for the 1.5 MW WindPACT blade, and the first flap wise and edgewise modes are shown to dominate flutter for the rotor speeds considered.
Download or read book Development of a Linearized Unsteady Aerodynamic Analysis for Cascade Gust Response Predictions written by National Aeronautics and Space Adm Nasa and published by Independently Published. This book was released on 2018-11-02 with total page 68 pages. Available in PDF, EPUB and Kindle. Book excerpt: A method for predicting the unsteady aerodynamic response of a cascade of airfoils to entropic, vortical, and acoustic gust excitations is being developed. Here, the unsteady flow is regarded as a small perturbation of a nonuniform isentropic and irrotational steady background flow. A splitting technique is used to decompose the linearized unsteady velocity into rotational and irrotational parts leading to equations for the complex amplitudes of the linearized unsteady entropy, rotational velocity, and velocity potential that are coupled only sequentially. The entropic and rotational velocity fluctuations are described by transport equations for which closed-form solutions in terms of the mean-flow drift and stream functions can be determined. The potential fluctuation is described by an inhomogeneous convected wave equation in which the source term depends on the rotational velocity field, and is determined using finite-difference procedures. The analytical and numerical techniques used to determine the linearized unsteady flow are outlined. Results are presented to indicate the status of the solution procedure and to demonstrate the impact of blade geometry and mean blade loading on the aerodynamic response of cascades to vortical gust excitations. The analysis described herein leads to very efficient predictions of cascade unsteady aerodynamic response phenomena making it useful for turbomachinery aeroelastic and aeroacoustic design applications. Verdon, Joseph M. and Hall, Kenneth C. Unspecified Center...
Download or read book Scientific and Technical Aerospace Reports written by and published by . This book was released on 1995 with total page 704 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Zinnenverzinzin Kinderboekenweek 2008 written by and published by . This book was released on 2008 with total page 236 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Aeronautical Engineering written by and published by . This book was released on 1991 with total page 538 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Applied mechanics reviews written by and published by . This book was released on 1948 with total page 400 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Japanese Science and Technology written by and published by . This book was released on 1986 with total page 724 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book NASA SP written by and published by . This book was released on 1992 with total page 444 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book A Comparative Study of Two Solution Methods for Blade Momentum Equations Used in the Aerodynamic Analysis and Design of Wind Turbines written by Min Mou and published by . This book was released on 2016 with total page 63 pages. Available in PDF, EPUB and Kindle. Book excerpt: The Blade Element Momentum (BEM) equations are widely used for analyzing the wind turbine aerodynamics and for turbine blade design. Compared to the classical approach to the solution of BEM equations which is relatively complex and can sometime lead to non-convergent solution, recently Andrew Ning has described a simpler solution method that reduces the solution to the BEM equations to a one-dimensional root-finding algorithm. In the Ning's approach, the Blade Element Momentum equations are determined for a blade inflow angle instead of the axial and tangential induction factors used in the classical BEM method. This approach simplifies the solution method and also leads to guaranteed convergence. In this thesis, the solution from new approach is compared to the numerical solution from the classical method by comparing the results with the experimental data for the NREL Phase II and Phase III, and Risoe horizontal axis wind turbines. In the BEM formulation, tip-loss correction factor influences the accuracy of the solution. The traditional tip-loss correction factor used is due to Prandtl and Glauert which is not always consistent with the physical behavior of the flow field near the tip. This research formulates a new more physically correct analytical expression for the tip losses and the results are compared with those obtained using the Prandtl-Glauert tip loss correction.
Download or read book Subsonic Aerodynamics written by Ion Paraschivoiu and published by Presses inter Polytechnique. This book was released on 2003 with total page 568 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Calculated Unsteady Aerodynamics of Wings written by James E. McCune and published by . This book was released on 1987 with total page 55 pages. Available in PDF, EPUB and Kindle. Book excerpt: Substantial advances in the analysis of the large-amplitude unsteady aerodynamics of wings have been achieved. Special focus has been placed on developing techniques for describing the exact non-linear convection, deformation, and roll-up of the vorticity wakes above and behind active wing surfaces. Using a combination of analytic and computer-interactive methods, new insights and more exact aerodynamic performance results have been generated. The effects of dissipative internal 'cores' in the overall 3D wake structures above deltas have been analyzed in the slender wing limit. New paths for further computer-assisted advances, including improved understanding of wing-wake interaction in severe maneuver, vortex core formation and break-up, and aerodynamic history effects have been charted. Papers are included on the following topics: Nonlinear aerodynamics of two-dimensional airfoils in severe maneuver; Interactive aerodynamics of wings in severe maneuver; Slender wing theory including regions of embedded total pressure loss; Keywords: Unsteady wing theory; Wake evolution; Vortex core evolution; Flight maneuvers; Unsteady wing loads; Flight loads.
Download or read book International Aerospace Abstracts written by and published by . This book was released on 1999 with total page 1042 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book NASA Scientific and Technical Publications written by and published by . This book was released on 1987 with total page 410 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book A method for predicting unsteady aerodynamic forces on oscillating wings with thickness in transonic flow near mach number 1 written by Koji Isogai and published by . This book was released on 1974 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
