Fluid-structure interaction of a wind turbine blade employing a refined finite element model coupled with a blade-element momentum method

Typically the aero-elastic simulation tools that are used in industry employ simple beam models to represent the blades of a wind turbine. The aerodynamic loads are usually calculated using a fast blade-element momentum (BEM) method. These models allow relatively fast calculation of the aero-elastic behavior of the blade which is required in order to allow the simulation of a large number of load cases as required by the IEC 61400 [1] and GL [2] standards in a feasible amount of time. Such beam models do however not incorporate the level of detail required to provide the complete stress and strain distribution in the blade, nor are they able to take into account nonlinear effects such as the change in cross-section of the blade due to the brazier effect [3]. Alternatively, highly detailed 3d computational fluid dynamics (CFD) simulations can be coupled with refined finite element (FE) models to obtain highly accurate results both regarding the flow around the blade as regarding the stress and strain distribution within the structure. However, the computational cost of such a simulation is enormous. In this work a coupling has been developed between the BEM code HAWC2-aero, which was developed by DTU [4] and the Abaqus FE solver. This allows a fluid-structure interaction (FSI) simulation by means of a so-called “weak” coupling, meaning that the two different solvers are run sequentially in iterations until convergence is achieved. In this way, a refined structural model is coupled with a fast aerodynamics tool, allowing steady-state fluid-structure interaction (FSI) simulations at an acceptable computational cost. The more advanced structural model allows the investigation of the influence of structural properties such as individual composite plies as well as their positioning, orientation and materials on the aero-elastic behavior of the blade. The influence of non-linear effects on the blade’s aero-elastic behavior can also be analyzed. The finite element model is used to locate stress hot-spots or buckling effects. Loads were applied using two different methods. One method uses distributing couplings to spread the load of a spanwise cross-section over all the nodes on that section. The other method uses concentrated forces at specific nodes to introduce the loads

The concept of segmented wind turbine blades : a review

There is a trend to increase the length of wind turbine blades in an effort to reduce the cost of energy (COE). This causes manufacturing and transportation issues, which have given rise to the concept of segmented wind turbine blades. In this concept, multiple segments can be transported separately. While this idea is not new, it has recently gained renewed interest. In this review paper, the concept of wind turbine blade segmentation and related literature is discussed. The motivation for dividing blades into segments is explained, and the cost of energy is considered to obtain requirements for such blades. An overview of possible implementations is provided, considering the split location and orientation, as well as the type of joint to be used. Many implementations draw from experience with similar joints such as the joint at the blade root, hub and root extenders and joints used in rotor tips and glider wings. Adhesive bonds are expected to provide structural and economic efficiency, but in-field assembly poses a big issue. Prototype segmented blades using T-bolt joints, studs and spar bridge concepts have proven successful, as well as aerodynamically-shaped root and hub extenders

Numerical investigation of the effect of tower dam and rotor misalignment on performance and loads of a large wind turbine in the atmospheric boundary layer

A modern horizontal axis wind turbine was simulated by means of computational fluid dynamics (CFD) simulations. The analyzed machine has a diameter of 100 m and is immersed in the atmospheric boundary layer (ABL). The velocity and turbulence stratification of the ABL is correctly preserved along the domain by the adoption of modified wall functions. An overset technique is employed to handle the rotation of the turbine rotor throughout the operation of the machine. The ABL induces periodically oscillating loads and generated torque on the rotor blades. Several configurations are analyzed. First, the results of a rotor-only simulation are compared to the ones obtained from the simulation of the full machine in order to evaluate the effect of the supporting structures on the produced torque and on the loads acting on the blades. Then, a tilt angle is introduced on the analyzed rotor and its effect on the oscillating loads of each blade is highlighted by comparing the results to the untilted configuration. Lastly, a yaw misalignment is also introduced and the results are compared to the unyawed configuration

Fluid–structure interaction simulations of a wind gust impacting on the blades of a large horizontal axis wind turbine

The effect of a wind gust impacting on the blades of a large horizontal-axis wind turbine is analyzed by means of high-fidelity fluid-structure interaction (FSI) simulations. The employed FSI model consisted of a computational fluid dynamics (CFD) model reproducing the velocity stratification of the atmospheric boundary layer (ABL) and a computational structural mechanics (CSM) model loyally reproducing the composite materials of each blade. Two different gust shapes were simulated, and for each of them, two different amplitudes were analyzed. The gusts were chosen to impact the blade when it pointed upwards and was attacked by the highest wind velocity due to the presence of the ABL. The loads and the performance of the impacted blade were studied in detail, analyzing the effect of the different gust shapes and intensities. Also, the deflections of the blade were evaluated and followed during the blade's rotation. The flow patterns over the blade were monitored in order to assess the occurrence and impact of flow separation over the monitored quantities

The effect of gravity in transient fluid-structure interaction simulations of a large wind turbine with composite blades

In this work the effect of the gravity force on the fluid-structure interaction (FSI) simulation of a large horizontal axis wind turbine (HAWT) is analyzed in detail. FSI simulations with and without gravity are carried out and compared in order to highlight the effect of gravity force on the loads and performance of the analyzed HAWT

Comparison of shell and solid finite element models for the static certification tests of a 43 m wind turbine blade

A commercial 43 m wind turbine blade was tested under static loads. During these tests, loads, displacements, and local strains were recorded. In this work, the blade was modeled using the finite element method. Both a segment of the spar structure and the full-scale blade were modeled. In both cases, conventional outer mold layer shell and layered solid models were created by means of an in-house developed software tool. First, the boundary conditions and settings for modeling the tests were explored. Next, the behavior of a spar segment under different modeling methods was investigated. Finally, the full-scale blade tests were conducted. The resulting displacements and longitudinal and transverse strains were investigated. It was found that for the considered load case, the differences between the shell and solid models are limited. Thus, it is concluded that the shell representation is sufficiently accurate