Aeroelastic Effects Research Articles

Wind‐induced fatigue of large HAWT coupled tower–blade structures considering aeroelastic and yaw effects

SummaryAn efficient approach for predicting wind‐induced fatigue in large horizontal axis wind turbine coupled tower–blade structures subject to aeroelastic and yaw effects is presented. First, aerodynamic loads under yaw conditions are simulated based on the harmonic superposition method and modified blade element momentum theory, in which wind shear, tower shadow, tower–blade interactions, aeroelastic, and rotational effects are taken into account. Then, a nonlinear time‐history of wind‐induced responses under simulated aerodynamic loads is obtained. Finally, based on these results, wind‐induced fatigue damage and lifespan are predicted according to linear cumulative damage theory. For completeness, the influences of mean wind speed, aeroelasticity, and yaw angle on horizontal axis wind turbine fatigue life are discussed. The results indicate that the aerodynamic loads and residual fatigue life can be estimated accurately by the proposed model, which can be used to simulate the 3D wind fields of wind turbines under given wind conditions. The wind energy of the wind turbine blade is mainly concentrated at its edge and is weaker at the hub. Estimation of wind turbine fatigue life is therefore suggested to be based on the component with the shortest life, being the blade root. Furthermore, yaw conditions significantly shorten fatigue life and should not be ignored. Fatigue life is also rather sensitive to mean wind speed.

Data-driven modeling of vortex-induced vibration of a long-span suspension bridge using decision tree learning and support vector regression

In recent years, vortex-induced vibrations (VIVs) have been observed on a few long-span bridges. Although a number of studies of VIV on structures have been conducted, and semi-empirical models have been proposed based on wind tunnel experiments, it is very difficult to accurately simulate the VIVs of prototype full-scale structures because of the complicated associated wind conditions, the Reynolds number effect, three-dimensional (3D) aeroelastic effects, uncertainties in the dynamic structure model, etc. In this paper, a data-driven approach using a machine learning (ML) scheme is proposed to model VIV response based on a database of field-measured VIVs for a full-scale long-span suspension bridge over six recent years. First, a decision tree learning algorithm is adopted to train the VIV mode classification model by mapping the relationship between wind characteristics and VIV mode; this can be employed to automatically identify VIV modes. Next, a support vector regression (SVR) algorithm is employed to model the VIV response of the bridge deck in the time domain for separate VIV modes. In this ML scheme, the wind speeds and wind directions at three different locations along the bridge span are used as the exogenous inputs of the classification model and regression model, taking the nonuniformity of the wind field into account. For the regression model, the VIV response at a previous step is also involved as an additional input variable. The trained models are validated for a few measured VIV events, which are randomly selected from the field measurement database. Further, the parametric analysis of the VIV response is performed using the trained model. The results indicate that the classification model and regression model can, respectively, accurately identify and predict the VIV response for various modes of the investigated bridge. The wind speed, wind direction, and nonuniformity are the critical parameters for the overall process (developing stage, steady stage, and vanishing stage) and amplitude of the VIV response.

Study on the aeroelastic responses of a wind turbine using a coupled multibody-FVW method

Abstract The present study aimed at developing an aeroelastic method of a wind turbine and highlighting the influences of aeroelasticity on both the aerodynamic and the structural performances. System's governing equations considering the aeroelastic effects of large scale wind turbines are derived by coupling a multibody method with a free vortex wake (FVW) method. The resulting differential-algebraic equations (DAE) are transformed to algebraic equations whose Jacobian matrices are difficult to be calculated. Based on an inverse Broyden-Fletcher-Goldfarb-Shanno (BFGS) approach, a quasi-Newton method with a suitable linear search is developed and used to solve those nonlinear equations, thus a new aeroelastic method without Jacobian matrices calculation is proposed. The time domain aeroelastic responses of the NH1500 1.5-MW wind turbine are obtained. The simulation results indicate that aeroelasticity of a blade has significant effects on the wake geometries and structural responses. Flexibility of the tower can cause more violent fluctuations for the power and loads compared with the results of a blade, which can considerably affect the blade fatigue life design.

Comparison of different dynamic models for floating wind turbines

There are different approaches utilized to establish dynamic models for floating offshore wind turbines, but their distinction and applicability are often confusing. This paper presents the theories about four different dynamic models developed for simulating floating wind turbines, including a single-rigid-body model, a corrected single-rigid-body model, a multi-rigid-body model, and a multi-rigid-flexible-body model. Subsequently, a series of comparisons between the four dynamic models are conducted to assess their differences and applicability for simulating floating offshore wind turbines. The results show that the multi-rigid-flexible-body model is most accurate but most time-consuming. In most cases, the multi-rigid-body model and the multi-rigid-flexible-body model can be performed, except for the aeroelastic effects and global dynamic responses caused by the vibration of the tower and blades. In contrast, the single-rigid-body model has simpler dynamical methodologies and less computational cost. However, it has some internal limitations, for instance, limited degrees of freedom, neglecting aeroelastic effects, neglecting gyroscopic effects, etc. Hence, the corrected single-rigid-body model is proposed and performs better than the original single-rigid-body model at the cost of a little time-consumption.

Aeroelastic effect on modal interaction and dynamic behavior of acoustically excited metallic panels

This paper details the study of the aeroelastic effect on modal interaction and dynamic behavior of acoustically excited square metallic panels with fully clamped edges using finite element method. The first-order shear deformation plate theory and von Karman nonlinear strain–displacement relationships are employed to consider the structural geometric nonlinearity caused by large vibration deflections. Piston aerodynamic theory and Gaussian white noise are used to simulate the aerodynamic load and the acoustic load, respectively. Motion equations are derived by the principle of virtual work in the physical coordinates and then transformed into the truncated modal coordinates with reduced orders. Runge–Kutta method is employed to obtain the system response, and the modal interaction mechanism is quantitatively valued by the modal participation distribution. Results show that in the pre-/near-flutter regions, in addition to the dominant fundamental resonant mode, the first twin companion antisymmetric modes can be largely excited by the aeroelastic coupling mechanism; thus, aeroelastic modal participation distribution and the spectrum response can be altered, while the dynamic behavior still exhibits linear random vibrations. In the post-flutter region, the dominant flutter motion can be enriched by highly ordered odd order super-harmonic motion occurs due to 1:1 internal resonances. Correspondingly, the panel dynamic behavior changes from random vibration to highly ordered motions in the fashion of diffused limit-cycle oscillations (LCOs). However, this LCOs motion can be affected by the intensifying acoustic excitation through changing the aeroelastic modal interaction mechanism. Accompanied with these changes, the panel can experience various stochastic bifurcations.

Design of Dynamic Systems Using Surrogate Models of Derivative Functions

Optimization of dynamic systems often requires system simulation. Several important classes of dynamic system models have computationally expensive time derivative functions, resulting in simulations that are significantly slower than real time. This makes design optimization based on these models impractical. An efficient two-loop method, based on surrogate modeling, is presented here for solving dynamic system design problems with computationally expensive derivative functions. A surrogate model is constructed for only the derivative function instead of the simulation response. Simulation is performed based on the computationally inexpensive surrogate derivative function; this strategy preserves the nature of the dynamic system, and improves computational efficiency and accuracy compared to conventional surrogate modeling. The inner-loop optimization problem is solved for a given derivative function surrogate model (DFSM), and the outer loop updates the surrogate model based on optimization results. One unique challenge of this strategy is to ensure surrogate model accuracy in two regions: near the optimal point in the design space, and near the state trajectory in the state space corresponding to the optimal design. The initial evidence of method effectiveness is demonstrated first using two simple design examples, followed by a more detailed wind turbine codesign problem that accounts for aeroelastic effects and simultaneously optimizes physical and control system design. In the last example, a linear state-dependent model is used that requires computationally expensive matrix updates when either state or design variables change. Results indicate an order-of-magnitude reduction in function evaluations when compared to conventional surrogate modeling. The DFSM method is expected to be beneficial only for problems where derivative function evaluation expense, and not large problem dimension, is the primary contributor to solution expense (a restricted but important problem class). The initial studies presented here revealed opportunities for potential further method improvement and deeper investigation.

Gust response and body freedom flutter of a flying-wing aircraft with a passive gust alleviation device

The effectiveness of a passive gust alleviation device (PGAD) mounted at the wingtip of aircraft in conventional and flying-wing configurations have been studied in previous research. However the PGAD influence on the aeroelastic stability in particular the body freedom flutter (BFF) of a flying-wing aircraft remains as a concern. This present investigation is focused on evaluating the beneficial effect of PGAD on both gust load alleviation and BFF of a small flying-wing aircraft of high aspect ratio wing made of composite. A small range of (1-cos) type of gust load has been considered to select a representative critical gust load case for the study. A parametric study indicates that there is a narrow band of optimal key parameters for the PGAD design. Subsequently a set of optimal parameters is selected to further the analysis of the PGAD mechanism. The case study results show that the PGAD can make the bending moment at the wing root due to gust reduced by 16%. In addition, the BFF speed of the flying-wing aircraft is increased by 4.2%. The investigation reveals that the PGAD mode and its interaction with the wing bending mode and short period oscillation of the aircraft can have beneficial aeroelastic effect on both gust alleviation and flutter suppression.

Effect of orthotropy ratio of the shear web on the aero-elasticity and torque generation of a hybrid wind turbine blade

The present work is concerned with the design of an improved turbine blade which reduces the aeroelastic effect and increases the output torque. The NPS100 rotor is taken as the baseline blade and modelled in NuMAD. The rotor is analysed for actual wind load computed using the Blade Element Momentum theory and an improved design of the NPS100 is suggested having different aerofoil profiles throughout the span. The effect of aero-elasticity on the output power generation is studied and a method to minimize the aeroelastic coupling is proposed.

TAS Code, FaSTAR, and Cflow Results for the Sixth Drag Prediction Workshop

Three mixed-element unstructured Reynolds-averaged Navier–Stokes solvers, the TAS code, FaSTAR, and Cflow, were applied to the Sixth AIAA Drag Prediction Workshop test cases to investigate the accuracy of the solvers with committee-provided grids and custom participant-generated grids by MEGG3D, BOXFUN, and the Cflow built-in grid generator. Solutions were obtained for the verification study using the two-dimensional NACA 0012 airfoil (test case 1), the NASA common research model nacelle–pylon drag incremental study (test case 2), and the common research model wing/body static aeroelastic effect study (test case 3). In test case 1, the three solvers used the same turbulence model, the Spalart–Allmaras one-equation turbulence model without the trip term for transition and without the ft2 function, and their grid convergence trends for lift, drag, and pitching moment coefficients were similar to that of FUN3D, CFL3D, and TAU. In test case 2, the TAS code with the NASA GeoLab grids and with MEGG3D grids, FaSTAR with the NASA GeoLab grids, and Cflow with its own grids predicted nacelle–pylon drag increment well. In test case 3, the three solvers predicted force and moment fairly comparable with experiment if support system interference effects were considered.

Numerical Investigations of the NASA Common Research Model with Aeroelastic Twist

Numerical investigations of the NASA Common Research Model from the 6th AIAA CFD Drag Prediction Workshop are performed with in-house solver MFlow. The solver is based on a cell-centered finite volume method and is capable of handling various element types. Hybrid grids supplied by the committee and generated in-house are used in the simulations. Grid convergence properties, polar lines, and pressure distributions are analyzed and compared with experimental data. A nearly linear convergence property is achieved with grid refinement for own-generated hybrid grids. The drag increment due to nacelle and pylon is well predicted. As angle of attack increases, the simulations with the original Spalart–Allmaras or shear-stress transport model exhibit a large side-of-body separation, whereas the results obtained with quadratic constitutive relation present a negligible separation bubble, which is more reasonable judging from experimental data. The solver shows good agreement with experiment. The predictions are much improved with the static aeroelastic effect considered in simulations.

Numerical studies of static aeroelastic effects on grid fin aerodynamic performances

The grid fin is an unconventional control surface used on missiles and rockets. Although aerodynamics of grid fin has been studied by many researchers, few considers the aeroelastic effects. In this paper, the static aeroelastic simulations are performed by the coupled viscous computational fluid dynamics with structural flexibility method in transonic and supersonic regimes. The developed coupling strategy including fluid–structure interpolation and volume mesh motion schemes is based on radial basis functions. Results are presented for a vertical and a horizontal grid fin mounted on a body. Horizontal fin results show that the deformed fin is swept backward and the axial force is increased. The deformations also induce the movement of center of pressure, causing the reduction and reversal in hinge moment for the transonic flow and the supersonic flow, respectively. For the vertical fin, the local effective incidences are increased due to the deformations so that the deformed normal force is greater than the original one. At high angles of attack, both the deformed and original normal forces experience a sudden reduction due to the interference of leeward separated vortices on the fin. Additionally, the increment in axial force is shown to correlate strongly with the increment in the square of normal force.

Effects of aeroelasticity on the performance of hypersonic inlet

Effects of the aeroelasticity on the performance of the hypersonic inlet have been investigated numerically in this study. The aeroelasticity has been simulated using the coupled computational fluid dynamics/computational structural dynamics method, which is solved by the in-house code. The unsteady Reynolds-averaged Navier–Stokes equations have been solved in the computational fluid dynamics simulation, and the modal method has been adopted in the computational structural dynamics simulation. Two cases have been utilized to validate the numerical method. Finally, the aeroelasticity has been simulated for inlet plate with different thicknesses. The effects of aeroelasticity on performance parameters and flow structure have been discussed in detail. The results show that the generalized displacements present the “beat” phenomenon in the time domain. The power spectral density of the generalized displacements implies that the aeroelastic instability is mainly caused by the coupling between the fourth- and fifth-order modes. The time-average flow rate coefficient and pressure rise ratio increase relative to the initial value, while the total pressure recovery coefficient decreases. The fluctuation amplitude of the flow rate coefficient is small, while that of the total pressure recovery coefficient and pressure rise ratio are relatively large. Besides, the phases of the three performance parameters are greatly different. Furthermore, the aeroelasticity has significant effect on the shock wave structure especially at the exit of the inlet.

Experimental Nonlinear Control for Flutter Suppression in a Nonlinear Aeroelastic System

Experimental implementation of input–output feedback linearization in controlling the dynamics of a nonlinear pitch–plunge aeroelastic system is presented. The control objective is to linearize the system dynamics and assign the poles of the pitch mode of the resulting linear system. The implementation 1) addresses experimentally the general case where feedback linearization-based control is applied using as the output a degree of freedom other than that where the physical nonlinearity is located, using a single trailing-edge control surface, to stabilize the entire system; 2) includes the unsteady effects of the airfoil’s aerodynamic behavior; 3) includes the embedding of a tuned numerical model of the aeroelastic system into the control scheme in real time; and 4) uses pole placement as the linear control objective, providing the user with flexibility in determining the nature of the controlled response. When implemented experimentally, the controller is capable of not only delaying the onset of limit-cycle oscillation but also successfully eliminating a previously established limit-cycle oscillation. The assignment of higher levels of damping results in notable reductions in limit-cycle oscillation decay times in the closed-loop response, indicating good controllability of the aeroelastic system and effectiveness of the pole-placement objective. The closed-loop response is further improved by incorporating adaptation so that assumed system parameters are updated with time. The use of an optimum adaptation parameter results in reduced response decay times.

Urban Integration of Aeroelastic Belt for Low-Energy Wind Harvesting

In this modern age low-energy devices are pervasive especially when considering their applications in the built-environment. The multitude of low-energy applications extend from wireless sensors, radio-frequency transceivers, charging devices, cameras and other small-scale electronic devices. The energy consumptions of these devices range in the milliwatt and microwatt scale which is a result of continuous development of these technologies. Thus, renewable wind energy harnessed from the aeroelastic effect can play a pivotal role in providing sufficient power for extended operation with little or no battery replacement. An aeroelastic belt is a simple device composed of a tensioned membrane coupled to electromagnetic coils and power conditioning components. This simplicity of the aeroelastic belt translates to its low cost and overall modularity. The aim of this study is to investigate the potential of integrating the aeroelastic belt into the built environment using Computational Fluid Dynamics (CFD) simulations. The work will investigate the effect of various external conditions (wind speed, wind direction and physical parameters, positioning and sizing) on the performance of the aeroelastic belt. The results from this study can be used for the design and integration of low-energy wind generation technologies into buildings.

Improvement of Computational Results of NASA Airliner Model by Wing Modal Analysis

The NASA Common Research Model of an airliner was used for the evaluation of the effect of aeroelasticity on aerodynamic forces and local flowfield. A computational fluid dynamics analysis of the rigid model showed large differences between the computational and experimental data. It was observed that the model (in particular, the wing) deformation has a significant effect on the aerodynamic characteristics. Online mesh deformation on the basis of wing modal analysis was used to improve the accuracy of the computational results. Twenty modes in total were used during coupled simulations. The results from these simulations showed that adding the wing deformation into the computational fluid dynamics simulation improved the accuracy of obtained aerodynamic coefficients. The same methodology was applied to the full-model configuration considering the deformation of all parts of the model. The results from the computational fluid dynamics analyses with online mesh deformation of the semispan and full model are the focus of this paper.

Aeroelastic and aerodynamic interference effects on a high-rise building

The 492m high Shanghai World Financial Centre is an interesting high-rise building in that the cross-section varies with the height. It is surrounded by a number of other buildings, including some of about half the height of it, a slightly lower nearby Jin Mao building, and a higher Shanghai Centre (not considered here). A series of wind tunnel tests for aeroelastic model vibration measurement and rigid model pressure measurement were carried out to investigate the aeroelasticity and aerodynamic interference effects on this building. The results show that, the densely clustered high-rise buildings (excluding the Jin Mao building) located upstream may cause the mean positive pressures of the lower obscured surface of the World Financial Centre to decrease, and the RMS pressures to increase or decrease for different configuration, which would exert some influences on the average and RMS responses. When buildings are located downstream, the wind-induced aerodynamic interference is negligible. When the Jin Mao building lies upstream, the mean positive pressures on the obscured surface of the World Financial Centre would decrease and even may become negative (the maximum absolute values may increase obviously), and the RMS pressures may also increase significantly, which cause the average displacement responses along-wind to reduce, the RMS horizontal displacement responses to increase, and the rotational displacement responses to increase for asymmetrical pressure. Moreover, it will weaken the energy and periodicity of vortex shedding of the World Financial Centre so as to reduce the possibility or amplitude of vortex resonance. More specifically, when the Jin Mao building lies downstream, the interference effects of the wind loads and wind-induced vibration of rigid World Financial Centre are less obvious, however, when the aeroelasticity is considered at the same time, a significant vortex resonance arose in the direction along the first order modal of the World Financial Centre at a lower wind speed, for which the natural frequency is close to the vortex shedding frequency. The findings derived from the present study are believed to be useful to gain further insight into the aeroelasticity and aerodynamic interference effects of high-rise buildings.

Stability of dynamic response of suspension bridges

The potential occurrence of internal parametric resonance phenomena has been recently indicated as a potential contributory cause of the appearance of critical dynamic states in long-span suspension bridges. At the same time, suspension bridges, in view of their flexibility, are prone to aeroelastic response, such as vortex shedding, torsional divergence and flutter. In this paper, a non-linear dynamic model of a suspension bridge is devised, with the purpose of providing a first attempt toward a unified framework for the study of aeroelastic and internal resonance instabilities. Inspired by the pioneering work of Herrmann and Hauger, the analyses have been based on a linearized formulation that is able to represent the main structural non-linear effects and the coupling given by aerodynamic forces. The results confirm that the interaction between aeroelastic effects and non-linear internal resonance leads to unstable conditions for wind speeds which can be lower than the critical threshold for standard aeroelastic predictions.

Structural Optimization Design of Large Wind Turbine Blade considering Aeroelastic Effect

This paper presents a structural optimization design of the realistic large scale wind turbine blade. The mathematical simulations have been compared with experimental data found in the literature. All complicated loads were applied on the blade when it was working, which impacts directly on mixed vibration of the wind rotor, tower, and other components, and this vibration can dramatically affect the service life and performance of wind turbine. The optimized mathematical model of the blade was established in the interaction between aerodynamic and structural conditions. The modal results show that the first six modes are flapwise dominant. Meanwhile, the mechanism relationship was investigated between the blade tip deformation and the load distribution. Finally, resonance cannot occur in the optimized blade, as compared to the natural frequency of the blade. It verified that the optimized model is more appropriate to describe the structure. Additionally, it provided a reference for the structural design of a large wind turbine blade.

Small morphing wing aerial vehicle dynamic modelling basing on simulation and flight test

Morphing wings can be more stable and more robust to gust in the flow of low Reynolds number compared with normal fixed wings. In contrast to big airplanes, small ones with morphing wings can rely on passive wing deformation to reduce disturbance rather than active control by multi-control surfaces. Engineering modelling for the prototype in the paper ignores aeroelastic effect because of the small deformation amount in terms of static aeroelasticity and high modal frequency in terms of dynamic aeroelasticity. Aerodynamic coefficients are determined through flight test and software calculation. An accurate trim condition is solved using a 6DOF flight model. The preciseness of the trim result is proved by comparing experiment results. The longitudinal and lateral state-space equations benchmarked against trim point is built. Dynamic response of the non-control perturbation motion are analysed.

The influence of material properties on the aeroelastic behavior of a composite wind turbine blade

The main objective of this research is to investigate the degree to which variations in mechanical properties of constitutive composite materials can influence the aeroelastic behavior of a wind turbine blade. First, structural behavior of a full-scale wind turbine blade is evaluated from different aspects of bending, torsional and axial rigidities. For this purpose, simplified model of the blade is constructed and it is validated with experimental data of the full-scale blade. Then, a parametric study is performed to determine the most dominant mechanical properties which have a severe impact on the structural behavior of the blade. Identified dominant properties are varied randomly and independently. Thus, stochastic analysis is performed to investigate the variations in natural frequencies of the blade as the governing parameter in defining aeroelastic behavior. Finally, susceptibility of the blade to dynamics instability is also examined. Aeroelastic effects are found to have a stronger effect on the blade with lower material properties that lead to more power reduction.