Simulation Of Morphing Blades For Vertical Axis Wind Turbines

The simulation of flow through vertical axis wind turbine (VAWT) is characterized by unsteady flow where the blade experiences varying angles of attack and Reynolds number as it completes a cycle. Therefore, the lift generated also varies as a function of its rotational position relative to the incoming freestream velocity. In order to improve the performance of these turbines the blade can take advantage of smart materials developed for control surface actuation. The aim of this paper is to investigate the effect of morphing blades on the aerodynamic performance of the turbine blades. The study uses commercial software Ansys Fluent pressure-based solver to investigate the flow past the turbine blades by solving the 2D Unsteady Reynolds-Averaged Navier-Stokes (URANS) equations. In order to simulate the morphing blade for VAWT, a sliding mesh method is used to simulate the VAWT rotation while a user-defined function (UDF) is written for the blade morphing flexure motion. This entails the use of dynamic mesh smoothing to prevent the mesh from having negative cell volumes. Although the dynamic mesh strategy has been successful in preserving the cell quality, it has been shown that the proposed method of simulating the morphing blade on VAWT is inadequate due to unphysical solutions. Finally, the effect of morphing the blade is tested on a static airfoil case instead, where it is shown that stall is alleviated by morphing the blade trailing edge.

This study compares the performance of a Vertical Axis Wind Turbine with and without using morphing capabilities applied to its blades. It also explores the feasibility of applying moving mesh to model the morphing capability inside the software package STAR CCM+© in order to use Computational Fluid Dynamics (CFD) to analyze the flow's behavior. Particularly it is important to capture the presence of dynamic stall and vortex shedding at certain regions over the blade's path, which are associated with a decreased in the overall power coefficient. This work developed a methodology to analyze these morphing capabilities when applied over airfoils in 2D simulations, by using a combination of overset meshes and the morphing approach. The accuracy is verified by creating a baseline scenario and compare it against a benchmark case, while also testing for grid and time step sensitivity. The use of Reynold Averaged Navier Stokes equations was chosen, with Menter's SST k-omega as the turbulence model. Afterward, a maximum power coefficient curve was plotted by testing three airfoil's shapes as references, one forming the baseline case, while the other two delimiting the maximum deformation, marked as outward and inward cases. A final optimized case was tested, where the morphing was applied to strategic regions where the dynamic stall was highest, and where the shapes could ensure the maximum possible power output.This resulted in an improvement of 46.2% of the overall power coefficient.

There is a growing global demand for "clean" energy due to an increased mandate to reduce greenhouse gases. Wind energy has established itself as an economically competitive source due to major developments made in the efficiency and reliability of conversion systems. Currently, horizontal axis wind turbines (HAWTs) dominate the wind energy conversion market because of their high efficiency. However, recent advances in vertical axis conversion systems are closing the gap in efficiency. A novel flexible blade concept with the ability to morph and adapt to changing flow conditions was proposed by A. Beyene and T. Ireland, to address part load and performance issues encountered in wind energy conversion systems. The extension of these benefits to a vertical axis wind turbine (VAWT) would make wind technology a more competitive player in the energy market. A straight bladed vertical axis wind turbine (SB-VAWT) rotor was manufactured, to accommodate flexible and rigid blades. The performance and flexible behavior was studied in the department of mechanical engineering's low speed wind tunnel using a test rig that was built for this study. A mathematical model, validated using a high speed camera and finite element analysis, was developed to predict the magnitude and direction of blade morph. The results show that the coefficient of performance (CP) greatly depends on the tip speed ratio (TSR), i.e., the rigid blade has CP of 0.11 for a TSR of 1.6, whereas the morphing blade achieved a CP of 0.06 at a TSR of 1.13. Overall, the modified morphing blade has better performance at low RPMs, but the rigid blade performed better at high RPMs. It was observed that the VAWT equipped with flexible blades self-started in the majority of the experiments. The flexible blade's production of power at relatively low TSRs is a rare occurrence in the field. At high RPM, the centrifugal force overwhelmed the lift force, bending the blade out of phase in an undesired direction increasing drag and therefore reducing the CP. These results suggest that alterations to the current design must be made in order to account for the inertial forces experienced by blades in a vertical axis configuration.

The book contains the research contributions belonging to the Special Issue "Numerical Simulation of Wind Turbines", published in 2020-2021. They consist of 15 original research papers and 1 editorial. Different topics are discussed, from innovative design solutions for large and small wind turbine to control, from advanced simulation techniques to noise prediction. The variety of methods used in the research contributions testifies the need for a holistic approach to the design and simulation of modern wind turbines and will be able to stimulate the interest of the wind energy community.

The objective of this report is to provide turbulent wind analyses relevant to the design and testing of Vertical Axis Wind Turbines (VAWT). A technique was developed for utilizing high-speed turbulence wind data from a line of seven anemometers at a single level to simulate the wind seen by a rotating VAWT blade. Twelve data cases, representing a range of wind speeds and stability classes, were selected from the large volume of data available from the Clayton, New Mexico, Vertical Plane Array (VPA) project. Simulations were run of the rotationally sampled wind speed relative to the earth, as well as the tangential and radial wind speeds, which are relative to the rotating wind turbine blade. Spectral analysis is used to compare and assess wind simulations from the different wind regimes, as well as from alternate wind measurement techniques. The variance in the wind speed at frequencies at or above the blade rotation rate is computed for all cases, and is used to quantitatively compare the VAWT simulations with Horizontal Axis Wind Turbine (HAWT) simulations. Qualitative comparisons are also made with direct wind measurements from a VAWT blade.

Printed collection of 105 full-length, peer-reviewed technical papers.

Wind turbines are one of the fastest-growing energy sources. Based on their axis of rotation they fall into two basic categories: horizontal-axis wind turbines (HAWTs) and vertical-axis wind turbines (VAWTs). Darrieus VAWTs exploit aerodynamic lift. This study entails the vibration analysis of large vertical-axis Darrieus wind turbine blades. Very large wind turbines are becoming more abundant due to their ability to harvest greater wind power. VAWTs are less common than HAWTs for large wind applications, but have some favorable characteristics, for example in offshore applications, and so further development of large VAWTs is anticipated. However, VAWTs are known to have vibration issues. VAWT blade vibration is the focus of this work.The straight-bladed H-rotor/Giromill is the simplest type of VAWT. We first derive the equations of motion of a H-rotor blade modeled as a uniform straight elastic Euler-Bernoulli beam under transverse bending and twist deformation. The reduced-order model suggests the existence of periodic damping, periodic stiffness, and direct excitation generated by a cyclic aeroelastic load. The model also indicates spin softening, which could be detrimental as the turbines become large. Periodic damping and stiffness are examples of parametric excitation and are likely to carry over to other types of VAWT blades. Systems with parametric excitation have been studied with various methods. Floquet theory has been classically used to study the stability characteristics of linear systems with periodic coefficients, and has been commonly applied to Mathieu's equation, which represents a vibration system with periodic stiffness. We apply the Floquet theory combined with the harmonic-balance method to a linear vibration system with a periodic damping coefficient. Based on this theory, the approximated solution includes an exponential part, with an unknown exponent, and a periodic part. Our analysis investigates the initial conditions response, the boundaries of instability, and the characteristics of free response solution of the system. The coexistence phenomenon, in which some of the transition curves overlap so that the instability wedges disappear, is recovered in this approach, and is examined closely.An additional case of the parametric excitation is the combination of parametric damping and parametric stiffness. The Floquet-based analysis shows that the combined parametric excitation reshapes the stability characteristics, compared to the system with only parametric damping or stiffness and disrupts the coexistence which is observed in the parametric damping case.The aeroelastic forces encountered by the wind turbines can cause self-excitation in blades, the mechanism of which can be loosely modeled with van-der-Pol-type nonlinearity. We seek to understand the combined effect of parametric excitation and van der Pol nonlinearity, as both can induce instabilities and oscillations. The oscillator is studied under nonresonant conditions and secondary resonances, with and without external excitation. We analyze the system using the method of multiple scales and numerical solutions. For the case without external excitation, the analysis reveals nonresonant phase drift (quasi-periodic responses), and subharmonic resonance with possible phase drift or phase locking (periodic responses). Hard excitation is treated for nonresonant conditions and secondary resonances, and similar phenomena are uncovered.Some Darrieus VAWTs consist of curved blades. We lastly study the modal analysis of curved Darrieus wind-turbine blades and obtain the mode shapes and modal frequencies. The governing equations are derived using the fundamental deformation mechanics, and thin beam approximations are employed to express the strain and kinetic energies. The assumed-modes method is applied to the energies, and the Euler-Lagrange equation is used to discretize the equations of motion. Implementing these equations, mode shapes are calculated and mapped back onto the curved beam for visualization. This analysis is conducted for pinned-pinned and hinged-hinged blades. The results are compared with Finite element analysis using Abaqus and with the literature.

Advances in Wind Turbine Blade Design and Materials, Second Edition, builds on the thorough review of the design and functionality of wind turbine rotor blades and the requirements and challenges for composite materials used in both current and future designs of wind turbine blades. Reviews the design and functionality of wind turbine rotor blades Examines the requirements and challenges for composite materials used in both current and future designs of wind turbine blades Provides an invaluable reference for researchers and innovators in the field of wind

As the fastest growing source of energy in the world, wind has a very important role to play in the global energy mix. This text covers a spectrum of leading edge topics critical to the rapidly evolving wind power industry. The reader is introduced to the fundamentals of wind energy aerodynamics; then essential structural, mechanical, and electrical subjects are discussed. The book is composed of three sections that include the Aerodynamics and Environmental Loading of Wind Turbines, Structural and Electromechanical Elements of Wind Power Conversion, and Wind Turbine Control and System Integration. In addition to the fundamental rudiments illustrated, the reader will be exposed to specialized applied and advanced topics including magnetic suspension bearing systems, structural health monitoring, and the optimized integration of wind power into micro and smart grids.