Aeroelastic Analysis Tool Research Articles

Optimized blade mass reduction of a 10MW-scale wind turbine via combined application of passive control techniques based on flap-edge and bend-twist coupling effects

In the present work, the possibility of reducing the mass and thereby the capital cost of a 10 MW-scale wind turbine blade is assessed by applying passive load control techniques. Two passive load control methods are combined in the analysis; the bend-twist-coupling method, aiming at reducing operational loads and the flap-edge-coupling method, aiming at alleviating stall induced vibrations in parked or idling operation. The first is materialized through rotation of the composite material plies over the caps of the spar beam, while the second is attained through displacement of the caps in opposite directions. The assessment of the material reduction capacity is performed through optimization simulations. The optimization loop combines an in-house thin lamination tool for the computation of the blade beam properties and the distribution of stresses over the cross sections of the blade and an in-house comprehensive aeroelastic analysis tool that provides the design loads of the turbine. Optimization simulations indicate that an 8.3% reduction in mass can be achieved through moderate modification of the blade inner structure, i.e. concurrent rotation of the plies of the UD material on the caps by 5.8° and displacement in opposite directions of the spar caps by 3% of the chord length.

Simulation of oscillating trailing edge flaps on wind turbine blades using ranging fidelity tools

AbstractRecent research developments have indicated that substantial reduction of both the fatigue and ultimate loads can be achieved by adopting trailing edge (TE) flap control strategies. Their aeroelastic tools employ blade element momentum (BEM) aerodynamic models enhanced with a sectional 2D treatment of the TE flap, neglecting the 3D effect of the trailed vorticity in the vicinity of the moving flap. In the present paper, a cross comparison of the BEM‐based models used in the aeroelastic analysis tools against higher fidelity, free‐wake lifting line, and fully resolved CFD models is performed, with the aim to highlight limitations of the first. A second level of comparison assesses the differences among tools of the same level of fidelity from different research groups. Moreover, a number of engineering‐based correction models that are used in conjunction with BEM and account for the complex 3D trailed vorticity effect are assessed. Simulations of a stiff rotor configuration of the DTU 10 MW Reference Wind Turbine are performed for a prescribed, harmonic TE flap motion, and aerodynamic loads are compared at the sectional and rotor‐integrated level. For the studied stiff rotor with the chosen flaps configuration, the results of the code‐to‐code comparisons indicate that low‐fidelity BEM tools consistently predict 1P variations of the rotor thrust due to the TE flap motion, but fail to reproduce the details of the load distributions especially in the vicinity of the flap section. BEM‐based corrected models, which account for 3D‐induced velocity effects, provide load distribution predictions closer to higher fidelity free‐wake and CFD models.

A cross-sectional aeroelastic analysis and structural optimization tool for slender composite structures

A fully open-source available framework for the parametric cross-sectional analysis and design optimization of slender composite structures, such as helicopter or wind turbine blades, is presented. The framework—Structural Optimization and Aeroelastic Analysis (SONATA)—incorporates two structural solvers, the commercial tool VABS, and the novel open-source code ANBA4. SONATA also parameterizes the design inputs, postprocesses and visualizes the results, and generates the structural inputs to a variety of aeroelastic analysis tools. It is linked to the optimization library OpenMDAO. This work presents the methodology and explains the fundamental approaches of SONATA. Structural characteristics were successfully verified for both VABS and ANBA4 using box beam examples from literature, thereby verifying the parametric approach to generating the topology and mesh in a cross section as well as the solver integration. The framework was furthermore exercised by analyzing and evaluating a fully resolved highly flexible wind turbine blade. Computed structural characteristics correlated between VABS and ANBA4, including off-diagonal terms. Stresses, strains, and deformations were recovered from loads derived through coupling with aeroelastic analysis. The framework, therefore, proves effective in accurately analyzing and optimizing slender composite structures on a high-fidelity level that is close to a three-dimensional finite element model.

Analysis of the coupled aeroelastic wake behavior of wind turbine

With the development of wind energy in recent years, the aeroelastic performances and the wake characteristics of a wind turbine and their effect on the downstream wind turbine have become research priorities. However, traditional aeroelastic analysis tools based on the Blade Element Momentum theory (BEM) cannot calculate the wake characteristics of a wind turbine. This study focuses on the coupled aeroelastic wake behavior of the wind turbine and developed a new tool called ALFBM, which combines the Actuator Line Method (ALM) and the nonlinear finite element Beam theory. The coupled aeroelastic wake behavior of a single NREL 5 MW wind turbine under the inlet velocity of 8 m/s and 11.4 m/s are studied. The aerodynamic and structural results such as power, thrust, natural frequencies, and tip deflections are compared with the results of former researches to verify this new analysis tool. Also, these results show that the stress stiffening effect and the nonlinear bending effect significantly decrease the frequency of flapwise mode by 12.7% and the tip deflection by 31%. It is found that the modal shape of every asymmetry flapwise mode varies periodically during the wind turbine rotation. The wake results demonstrate that the recovery of the velocity and vorticity in the far wake region (>5D) are underestimated when the deformation of the wind turbine blades are neglected.

Nonlinear aeroelastic response of wind turbines using Simo-Vu-Quoc rods

• Combination of GEBT-based Simo-Vu-Quoc rods and BEMT for large wind turbines. • Lagrangian description obviates the need to explicitly define centrifugal/coriolis forces. • Aeroelastic coupling includes the effects of both structural deformations and vibration velocities. • Priming of aeroelastic solver by moderating structural response in the acceleration phase. • Asymptotic stability and orbital stability (limit-cycles) observed with and without gravity. A methodology is presented to obtain the nonlinear aeroelastic response of horizontal axis wind turbines using accurate and computationally efficient aerodynamic and structural descriptions. For computing the geometrically nonlinear deformations of the rotor blades , we employ Simo-Vu-Quoc’s geometrically exact finite-strain spatial rod model, which treats the displacements of the beam reference line and the rotations of the cross-section as configuration variables, without any restrictions on their magnitudes or those of the resulting 1-D strain measures. The structural description is Lagrangian, obviating the need for an explicit definition of centrifugal/coriolis forces. Towards the aerodynamic side, Blade Element Momentum Theory enhanced with several important corrections is employed, along with a dynamic stall model that accounts for the unsteady effects. A comprehensive treatment of the aeroelastic computations within the restrictions imposed by the aerodynamic theory is presented with the aid of a ‘shadow’ frame of reference rotating rigidly with the deforming blades. A novel strategy ‘primes’ the aeroelastic solver by moderating the response of rotor in its acceleration phase. An integrated MATLAB tool WindGEAR incorporating the two coupled codes is developed to simulate the fully-coupled aeroelastic response of the NREL 5 MW wind turbine. The results, when compared with published data, establish WindGEAR firmly as a robust wind turbine nonlinear aeroelastic analysis tool in time-domain.

Aeroelastic analysis of a floating offshore wind turbine in platform‐induced surge motion using a fully coupled CFD‐MBD method

AbstractModern offshore wind turbines are susceptible to blade deformation because of their increased size and the recent trend of installing these turbines on floating platforms in deep sea. In this paper, an aeroelastic analysis tool for floating offshore wind turbines is presented by coupling a high‐fidelity computational fluid dynamics (CFD) solver with a general purpose multibody dynamics code, which is capable of modelling flexible bodies based on the nonlinear beam theory. With the tool developed, we demonstrated its applications to the NREL 5 MW offshore wind turbine with aeroelastic blades. The impacts of blade flexibility and platform‐induced surge motion on wind turbine aerodynamics and structural responses are studied and illustrated by the CFD results of the flow field, force, and wake structure. Results are compared with data obtained from the engineering tool FAST v8.

Transition piece design for an onshore hybrid wind turbine with multiaxial fatigue life estimation

Steel tubular structures are somewhat entrenched for the wind turbine towers. Recently, steel hybrid lattice/tubular towers are being investigated as a conceivable answer for taller onshore wind turbines for which convectional steel tubular towers are less competitive. Hybrid lattice/tubular towers require a transition piece which serves as a connection between lattice and tubular part. As the transition piece is supposed to transfer all the dynamic and self-weight loads to the lattice and foundation, these structural elements present unique features and are critical components to design and ought to resist strong cyclic bending moments, shear forces, and axial loads. Well-designed transition pieces with optimized ultimate state and fatigue capacities for manufacturing contribute to the structural soundness, reliability, and practicability of new onshore wind turbines hybrid towers. This research focuses on the investigation of the transition piece for an onshore wind turbine hybrid tower. The 5-MW reference wind turbine and a hybrid lattice/tubular tower were simulated in the servo-hydro aero-elastic analysis tool (by ASHES software) from which the loads and dynamic response of the supporting structure were obtained. Cross-sectional forces at the transition piece elevation were calculated and the connection with the lattice structure is designed. The transition piece was designed by finite element model considering ultimate limit load and fatigue load, using nonlinear analysis and multiaxial fatigue for life-time prediction, respectively. Multiaxial fatigue life was calculated based on Brown–Miller and Smith–Watson–Topper methods. In comparison, Smith–Watson–Topper method comes out to be more conservative. Potential of using high-strength steel S690 was investigated.

On Advanced Control Methods toward Power Capture and Load Mitigation in Wind Turbines

Abstract This article provides a survey of recently emerged methods for wind turbine control. Multivariate control approaches to the optimization of power capture and the reduction of loads in components under time-varying turbulent wind fields have been under extensive investigation in recent years. We divide the related research activities into three categories: modeling and dynamics of wind turbines, active control of wind turbines, and passive control of wind turbines. Regarding turbine dynamics, we discuss the physical fundamentals and present the aeroelastic analysis tools. Regarding active control, we review pitch control, torque control, and yaw control strategies encompassing mathematical formulations as well as their applications toward different objectives. Our survey mostly focuses on blade pitch control, which is considered one of the key elements in facilitating load reduction while maintaining power capture performance. Regarding passive control, we review techniques such as tuned mass dampers, smart rotors, and microtabs. Possible future directions are suggested.

Aero-Structural Optimization of Three-Dimensional Adaptive Wings with Embedded Smart Actuators

The design of morphing wings involves the disciplines of aerodynamics and structural mechanics; the aero-structural coupling is of chief importance in case smart materials are used as distributed actuators. Considering these specific requirements, this paper presents an approach to optimize concurrently the variables describing the wing external shape, the internal compliant structure, and the embedded actuators. An aeroelastic analysis tool is developed to simulate the response of distributed compliance three-dimensional wings, considering the activation of the smart materials. A method to formulate the optimization requirements based on the aircraft mission is presented, using the aerodynamic performance from the aeroelastic study in the optimization goal. To prove the validity and the computational feasibility of this methodology, a morphing wing for a 3-m-wingspan radio-controlled plane is optimized. A structural concept actuated by single crystal Macro Fiber Composites and dielectric elastomers is introduced, and its compliant structure is parameterized using a novel compact Voronoi-based representation. The optimized wing design produces rolling moments sufficient to guarantee the controllability of the flight. Numerical evaluation of the aerodynamic efficiency shows that an optimal activation of the embedded actuators further increases the advantages of morphing outside the design condition with respect to rigid wings.

Multidisciplinary Simulations with the Coupling Library MpCCI

Extreme high demands on designing accurate prototypes for example in the fields of medical research, aircraft construction, shipbuilding and automotive industry require multidisciplinary simulations. A large number of tools for monodisciplinary simulations are available today. Each of these provides high quality simulation results in a specific physical domain. Now there is also a solution to do multidisciplinary computations: Parallel monodisciplinary codes are coupled with the Mesh based parallel Code Coupling Interface MpCCI to solve multidisciplinary problems with a loose coupled approach. The paper presents applications in the framework of fluid-structure interaction, which demonstrate the advantages of the parallel coupling library for this kind of problems. The computational fluid dynamics code FLOWer developed at the Institute of Design Aerodynamics/DLR and the structural mechanics code SIMPACK developed at the Institute of Aeroelasticity/DLR are coupled to solve an aeroelastic test problem. The applicability of the coupling library in the field of aeroelasticity is strongly dependent on the integrated interpolations between the involved meshes. In the Institute of Aeroelasticity the aeroelastic analysis tool CAESAR was developed which includes aeroelasticity specific interpolation algorithms. These routines are integrated in MpCCI via a special interface. There are two types of interpolation routines included. The first kind of algorithms is based on the method of finite interpolation elements and the second uses radial basis functions.

Aeroelastic tailoring analysis for preliminary design of advanced propellers with composite blades

An analytical study of aeroelastic tailoring has been conducted to determine the flutter characteristics of advanced turbo propellers for preliminary design purposes. The structural dynamic model for composite propeller blades is combined with an unsteady cascade theory with three-dimensional corrections to produce an aeroelastic analysis tool for pretwisted propeller blades with homogeneous anisotropy exposed to a high subsonic flow. The free-vibration analysis of the SR-3 propeller model built of unidirectiona l graphite/epoxy , revealed that the first-bending frequency of the blade can be changed by 53% from the baseline value by changing fiber orientation. Using/?-k modal flutter analysis it was also found that the fiber orientation with a little larger sweep angle than that of the elastic axis can eliminate flutter without any weight penalty, and that the corresponding first natural mode has the least bending-torsion coupling. However, the flutter velocity is sensitive to fiber orientation and interblade-phase angle.

Aeroelastic tailoring analysis for advanced turbo propellers with composite blades

The development of unsteady aerodynamic analysis with computational fluid dynamics important for investigating the aeroelastic characteristics of rotors made of advanced composite materials. The purpose of the present analysis is to establish an aeroelastic model useful for the preliminary design of advanced turbo propellers. An unsteady aerodynamic model of high subsonic cascade airfoils, including sweep effects and finite span effects, is combined with a structural dynamic model for composite pretwisted propeller blades to produce an aeroelastic analysis tool. The p-k modal flutter analyses for the SR-3 propeller model (made of graphite/epoxy) were conducted. They revealed that suitable combinations of the fiber orientation can eliminate flutter without any weight penalties or strength penalties and that the flutter velocity is found to be sensitive to the interblade phase angle as well as the fiber orientation. These results indicate the effectiveness of aeroelastic tailoring for advanced turbo propellers and also the usefulness of the present analysis.