Aeroelastic Response Research Articles

Hypersonic Aeroelastic Response of Elastic Boundary Panel Based on a Modified Fourier Series Method

In this paper, an analytical method is proposed to directly obtain the aeroelastic time domain response of the elastic boundary panel. Based on a modified Fourier series method (MFSM), the vibration analysis of elastic boundary panels is carried out, after the dynamics equation of the panel is obtained. Then, the vibrational functions are combined with the supersonic piston theory to establish the aeroelastic equation. The aeroelastic time domain response of the panel is obtained to analyze the flutter speed of the panel more intuitively. Finally, the flutter speeds of panels with different length-width ratios, thicknesses, and elastic boundary conditions are discussed in detail.

Nonlinear Aeroelastic Analysis of Large Wind Turbines Under Turbulent Wind Conditions

We investigate in this Paper the nonlinear aeroelastic response of large horizontal axis wind turbines under a stochastically simulated turbulent wind field, which is instantaneously sampled by the rotating and deforming blades of the rotor. The aeroelastic code combines the unsteady blade element momentum theory, equipped with several important corrections, with the displacement-based nonlinear finite element implementation of the geometrically exact beam theory. The structural model is both shearable and extensible and does not place any restrictions on the magnitudes of the configuration variables or those of the resulting one-dimensional strain measures. The aeroelastic coupling takes into account the beam axis deformations, elastic twist, and vibration-induced velocities. The three-component, three-dimensional turbulent wind field is obtained using the Mann spectrum, from which the instantaneously sampled wind speeds are extracted by spatiotemporal interpolation in the spirit of Taylor’s frozen turbulence hypothesis. The structural and unsteady aerodynamic analysis components of the aeroelastic code are validated using benchmark examples. A fully coupled nonlinear aeroelastic simulation is carried out for the National Renewable Energy Laboratory’s 5 MW research wind turbine. The influence of three-dimensional instantaneous sampling, transverse (lateral and vertical) components of turbulence, vertical wind shear, and flow unsteadiness on the aeroelastic response under turbulence is examined along with the effects of coupling parameters including the vibration-induced velocities and elastic twist of the rotor blades. The dominant frequency contributions in key aeroelastic response variables due to each of these effects are identified.

Energy Harvesting Performance of Plate Wing from Discrete Gust Excitation

Energy harvesting from aeroelastic response tends to have a wide application prospect, especially for small-scale unmanned aerial vehicles. Gusts encountered in flight can be treated as a potential source for sustainable energy supply. The plate model is more likely to describe a low aspect ratio, thin plate wing structure. In this paper, the Von Kármán plate theory and 3D doublet lattice method, coupled with a piezoelectric equation, are used to build a linear state-space equation. Under the load of “one-minus-cosine” discrete gust, the effects of flow speed and gust amplitude, thickness of piezoelectric ceramic transducer (PZTs) layers, and mounted load resistance are investigated. Results reveal that the PZTs layers on the wing root of the leading edge can obtain the highest electrical parameters. The flow velocity, thickness of the PZTs layers and load resistance are used to optimize energy harvesting data.

Geometrically nonlinear static aeroelastic analysis of composite morphing wing with corrugated structures

In this paper, an integrated geometrically nonlinear aeroelastic framework to analyze the static nonlinear aeroelastic response of morphing composite wing with orthotropic materials has been developed. A flat plate/shell finite element, which can model plate-like wings, has been accommodated to model composite/corrugated panels to investigate effects of different laminate orientations and corrugations. A corotational approach is used to consider the geometrical nonlinearity due to large deformation produced by wing morphing. An unsteady vortex-lattice method is implemented to couple with the structural model subject to the large deformations. A homogenization method is also implemented to model corrugated panels as equivalent orthotropic plates. Individual structural, aerodynamic, and corrugated panel models, as well as the complete nonlinear aeroelastic framework, are verified. Numerical studies explore the static aeroelastic responses of a flat wing with composite/corrugated panels. This work helps to understand the nonlinear aeroelastic characteristics of composite/corrugated wings and demonstrates the capability of the framework to analyze the nonlinear aeroelasticity of such morphing wings.

Experimental and theoretical correlations for energy harvesting from a large flapping flag response

Two experimental models are constructed, i.e. partially covered and fully covered, cantilevered plates with piezoelectric piezo patches and film sensors. Two different experimental methods are used to obtain large flapping vibrations, a mechanically forced vibration and a limit cycle oscillation from an aeroelastic responses. AC voltage outputs from the piezo patch or film sensors and a DC power extraction through a AC/DC converter circuit are obtained. These experiments are used to evaluate a new computational model and code for a piezoelectric-aeroelastic system.

Dynamic Data-Driven Multi-Step-Ahead Prediction with Simulation Data and Sensor Measurements

In this paper, the authors propose a dynamical data-driven prediction framework to estimate a system’s behavior multiple steps ahead. The main contribution of this work is in the construction of a new recursive multi-input/multi-output (REC-MIMO) strategy, which can attain real-time estimation through a combination of expensive simulation data (offline) and sensor measurements (online). This framework is composed of an offline phase and an online phase. In the offline phase, a multi-input/multi-output strategy is employed for constructing a predictive model for the system’s dynamical responses from simulation data. The offline phase is accomplished through a combination of proper orthogonal decomposition and Gaussian process. By using the measurement data collected from sensors, a recursive strategy is used to iteratively enhance multi-step-ahead predictions by using a new reduced-order particle filter method during the online phase. An illustrative example involving aeroelastic responses of a joined-wing SensorCraft is used to demonstrate the effectiveness of the proposed framework. It has been shown that state predictions obtained through the REC-MIMO strategy have accuracy comparable to those obtained from high-fidelity simulations with significant reduction in computational expense. It is envisioned that the proposed methodology can be used to support system decision making in an efficient manner.

On the validation of variable fidelity multi-physics simulations

The difficulties encountered in applying current normative approaches for validation to computational models of complex multi-physics engineering systems are identified and are associated with the untestable, and sometimes unprincipled, nature of these models. The behaviour of a structural panel on the surface of a hypersonic flight vehicle when subject to complex interactions between aerothermal, aeroelastic and material responses is employed as a key exemplar. A wide range of positions in the philosophy of science, that are applicable to validation, are discussed within the context of a schematic matrix, which allows models to be categorised according to whether they are testable and principled. In the absence of test data against which to assess the accuracy of predictions, it is proposed that a model's credibility should be established based on its epistemic values, theoretical ancestry and the credentials of the modelling techniques. This shift from an objectivist to a relativist approach requires the assignment of experts who acknowledge their biases while engaging intellectually and ethically with the model, the community of knowledge and stakeholders, in a hermeneutical approach.

Wing Elasticity Effects on Store Separation

The study explores wing elasticity effects on the store-separation process. The nominal test case is that of an unmanned aerial vehicle that carries two identical stores on two wing stations. The stores are ejected during straight and level flight at , 2500 m. Simultaneous, time-accurate analysis of the dynamic aeroelastic wing response and the store’s trajectory reveals that the most significant aeroelastic effect is a roll motion developed by the store. This roll motion is due to misalignment of the ejection force vector and the store’s center of gravity, due to the wing’s static and dynamic elastic deformations. The second part of the paper presents a parametric study of the effects of various structural and configurational parameters on the wing’s response and consequently on the store’s rolling motion. A more flexible wing, a heavier store, a larger ejection force, or a shorter ejection period all result in increased store rolling. Store ejection from an asymmetric configuration (of a single store) yielded a very similar store roll compared to the symmetric ejection. The dynamic wing response plays a major role in generating the store roll, in different conditions of friction between the store body and ejection piston. A practical observation is that the store roll is dependent on the relation between the ejection period and the low structural frequencies of the wing. This can be used to plan an optimal ejection profile.

Numerical simulations of wind circumfluence around a Tensairity cylindrical beam and predictions of its response

Numerical simulations of wind circumfluence around Tensairity cylindrical beams and predictions of their response are presented in the paper. An appropriate computational fluid dynamics model (CFD) and a fluid-structure interaction (FSI) method are used to study circumfluent wind fields and wind-induced vibrations of the Tensairity cylindrical beams. Navier-Stokes equations for the incompressible fluid dynamic simulations and FSI analysis of the Tensairity cylindrical beam subjected to the wind flow are applied. Constant and simulated fluctuating wind fields were assigned to the investigated structure. A Spalart-Allmaras (SA) one-equation turbulence model that uses an eddy-viscosity variable with a nonlinear transport equation was applied in the CFD analysis. The finite element method is used to simulate the aeroelastic behavior of the Tensairity cylindrical beam subjected to constant and fluctuating wind effects. Aeroelastic response characterized by wind velocity fields and vortex-shedding phenomena around the cross-section of the inflatable structure are presented. Results obtained from the CFD and FSI analysis were compared. The vortex shedding effects may produce significant lateral (cross-wind) vibrations with nonlinear redistributions of forces and displacements as well as introduce additional deformations to the individual structural members of the Tensairity system. The wind-structure interaction analysis of the Tensairity cylindrical beam revealed, in particular, the sensitivity of the pneumatic structure to vortex induced vibrations with galloping effects.

Aeroelastic Study for HART II Rotor Using Unstructured Mixed Meshes

In the present study, aeroelastic response of HART II rotor blade has been numerically investigated using a coupled CFD/CSD method. Aerodynamic forces were calculated from a Navier–Stokes CFD flow solver based on unstructured mixed meshes. In the mixed meshes methodology, body-fitted prismatic/tetrahedral mesh was used in the near-body flow region to handle complex geometries easily. Cartesian mesh was used in the off-body flow region and high-order accurate weighted essentially non-oscillatory scheme was employed to implement high-order spatial accuracy. In the FEM-based CSD solver, an elastic deformation of the rotor blade was obtained on the basis of nonlinear Euler–Bernoulli beam theory. The coupling between the CFD and CSD solver was performed in a loosely coupled manner by exchanging the aerodynamic loads and elastic deformation of the rotor blade. An overset mesh technique was adopted to simulate rotating motion of the rotor blade and to exchange flow information between two different meshes. In addition, spring analogy was used to implement elastic deformation of the rotor blade. Coupled CFD/CSD method was applied to the HART II rotor in forward flight to examine aerodynamic performance and aeroelastic effect of the rotor. Aerodynamic loads and elastic deformation of the rotor blade were calculated and compared with experimental results and other research efforts. Overall, the present results were in good agreement with the experimental data. In addition, adaptive fine mesh was used to capture tip vortex trajectory and BVI (blade–vortex interaction) phenomenon more accurately.

Dielectric Barrier Discharge Plasma Actuator for Load Alleviation and Instability Control in a Compressor Cascade

The aim of this study is to investigate the performance of dielectric barrier discharge plasma actuators (DBD-PAs) applied to control the aeroelastic response of a compressor cascade in subsonic flow conditions. Simulations involve a cascade composed by 7-blade, 3 of which show a not-synchronous pitching behaviour. Two different inter blade phase angle (IBPA) have been tested and compared. Actuators capabilities in terms of load alleviation and instability control have been evaluated through the measurement of mean value, standard deviation and hysteresis area of the airfoil response in terms of lift and moment coefficients.

Preliminary design of aeroelastically tailored wing box structures with bend-twist coupling

Nowadays the composite materials have become the materials of choice to be used in the new aerospace structures that need to be not only larger and larger in size but also to be better performing in terms of aeroelastic responses inherent to thin-walled, slender structures. The advantage of composite materials airframes stems from their low structural weight which determines lower fuel consumption while preserving at the same time the airworthiness of the designed aircraft. But more important than the fuel consumption, the composite materials allow for the optimal tailoring of its layers in terms of specific design objectives. The paper presents such an aeroelastically tailored load carrying wing model which can passively control specific aeroelastic effects. The article focuses on the bend-twist coupling of the structural response to aerodynamic forces and on the parameter estimation/model updating techniques used to characterize the finite element model of the composite wing. Results are compared and validated with analytical, numerical and experimental data available in published literature.

Nonlinear fluid-structure interaction of bridge deck: CFD analysis and semi-analytical modeling

Nonlinear behavior in fluid-structure interaction (FSI) of bridge decks becomes increasingly significant for modern bridges with increasing spans, larger flexibility and new aerodynamic deck configurations. Better understanding of the nonlinear aeroelasticity of bridge decks and further development of reduced-order nonlinear models for the aeroelastic forces become necessary. In this paper, the amplitude-dependent and neutral angle dependent nonlinearities of the motion-induced loads are further highlighted by series of computational fluid dynamics (CFD) simulations. An effort has been made to investigate a semi-analytical time-domain model of the nonlinear motion induced loads on the deck, which enables nonlinear time domain simulations of the aeroelastic responses of the bridge deck. First, the computational schemes used here are validated through theoretically well-known cases. Then, static aerodynamic coefficients of the Great Belt East Bridge (GBEB) cross section are evaluated at various angles of attack, leading to the so-called nonlinear backbone curves. Flutter derivatives of the bridge are identified by CFD simulations using forced harmonic motion of the cross-section with various frequencies. By varying the amplitude of the forced motion, it is observed that the identified flutter derivatives are amplitude-dependent, especially for A_2* and H_2* parameters. Another nonlinear feature is observed from the change of hysteresis loop (between angle of attack and lift/moment) when the neutral angles of the cross-section are changed. Based on the CFD results, a semi-analytical time-domain model for describing the nonlinear motion-induced loads is proposed and calibrated. This model is based on accounting for the delay effect with respect to the nonlinear backbone curve and is established in the state-space form. Reasonable agreement between the results from the semi-analytical model and CFD demonstrates the potential application of the proposed model for nonlinear aeroelastic analysis of bridge decks.

On aeroelastic response of an airfoil under dynamic stall using time delay neural network

To clarify the mechanism of the complex aeroelastic responses of flexible blades of helicopter rotors under dynamic stall, an aeroelastic system of a 2D airfoil forced to oscillate is investigated. A reduced-order model based on time delay neural network is introduced to cut down the cost in parametric study of the aeroelastic system. The model is validated against full-order model results both with and without elasticity, which is proved to be an accurate and computational efficient method. The model is then applied to study the influence of system’s natural frequency on the aeroelastic responses, and a phenomenon of secondary resonance is found in the results. Detailed investigation and full-order simulation are performed on the cases of secondary resonances. The phenomenon is believed to be associated with the strong aerodynamic nonlinearity under dynamic stall where the instability of the vortex shedding or interaction leads to subharmonics of the aerodynamic loads. When the structure’s natural frequency is coincident with the multiples of the subharmonic, secondary resonances happen.

A fully-coupled CFD/CSD computational approach for aeroelastic studies of helicopter blade-vortex interaction

Blade-vortex interaction (BVI) is one of the main sources of noise and vibrations in helicopters. The aeroelastic response of the blade, to BVI phenomenon, is one of the main factors affecting the helicopter's aerodynamic performance and stability. In the present research we developed and implemented a novel CFD-based, strong (two-way) time-domain coupling, mathematical model, for the numerical prediction of the aeroelastic response of the helicopter blade to BVI. Another novelty, of the fully coupled CFD/CSD approach, is that the fluid flow is solved using the large-eddy simulation (LES) approach. In the present research, the aeroelastic response of a symmetric NACA0012 airfoil to BVI is computed using a two-degree of freedom (2-DOF) mass/spring model. The numerical studies show that the blade-vortex offset distance, (h), plays a key role in the mechanism of BVI and therefore, it influences the aerodynamic coefficients. The computational studies show that the BVI phenomenon diminishes with the increase of the offset distance (h). Also, it was observed that the elastic nature of the airfoil acts as a damper and it diminishes the effect of BVI on the aerodynamic coefficients. Therefore, for a flexible airfoil, the lift coefficient exhibits a decay, at the instant of blade-vortex interaction, when compared with rigid airfoil.

An efficient implementation of aeroelastic tailoring based on efficient computational fluid dynamics-based reduced order model

Current and future trends in the aerospace industry leverage on the potential benefits provided by lightweight materials that can be tailored to realize desired mechanical characteristics when loaded. For aircraft design, the deployment of aeroelastic tailoring is hindered by the need to re-compute, for any possible modification of the structure, the dependence of the aerodynamic field on the underlying structural properties. To make progress in this direction, the work presents a rapid computational fluid dynamics based aeroelastic tool which is built around a reduced order model for the aerodynamics that is updated for any modification of the structure by using the structural dynamics reanalysis method. The aeroelastic tailoring tool is demonstrated in transonic flow for the AGARD 445.6 wing, suitably modified with composite materials. It was found that the proposed method provides accurate engineering predictions for the aeroelastic response and stability when the structure is modified from the baseline model.

Optimal locations of magnetorheological fluid pockets embedded in an elastically supported honeycomb sandwich beams for supersonic flutter suppression

In this paper, the optimal locations of finite number of embedded magneto-rheological fluid (MRF) pockets are calculated by using Single Objective Genetic Algorithm (SOGA) to suppress the supersonic flutter of an elastically supported sandwich beam with regular honeycomb interlayer. The structural formulation is based on the classical beam theory along with the Winkler-Pasternak foundation model, the MRF is modeled as a first order Kelvin-Voigt material, and the quasi-steady first order supersonic piston theory is employed to define the aerodynamic loading. The aeroelastic time response of honeycomb sandwich beams with different number of embedded MRF pockets are measured with/without foundation and flow stream under impact load. The simulation shows that by using MRF pockets in optimized locations in honeycomb sandwich structure, not only both lightness of honeycombs and variability of structural damping of MRF are considered, but also the supersonic flutter can be postponed to higher dynamic pressure compared to entirely honeycomb or MRF sandwich beams. Finally, in order to achieve the optimum compromise between mass and the flutter suppression, the best number of MR pockets along with the optimum magnetic field values in honeycomb sandwich structure is presented.

Effects of the pylon–store system on the nonlinear aeroelastic responses of a slender wing

The aeroelastic behaviors of wing–pylon–store system have been researched for several decades. However, the effects of pylon–store system on the nonlinear aeroelastic characteristics of slender wings have not been sufficiently understood. In this paper, the nonlinear aeroelastic properties of a slender wing with a pylon–store system are discussed. The nonlinear equations of motion about the wing–pylon–store system are established, where the nonlinearities about the wing deformation and store motion are considered. The aerodynamic loads on the wing are determined by using two aerodynamic models with strip theory. One is the linear unsteady aerodynamic model based on Wagner function, the other is the nonlinear ONERA aerodynamic model. By comparing the nonlinear responses obtained with different aerodynamic models, it is found that the interaction between the aerodynamic nonlinearities induced by dynamic stall and the structural nonlinearities may simplify the bifurcation diagram structure of the system. For some typical cases of the wing–pylon–store system, the aeroelastic responses are analyzed. It is observed that the store-induced kinematic nonlinearities may affect the bending oscillation equilibrium position of the wing. This effect will be reduced by using soft spring in the pylon. Additionally, in the case of pylon with soft spring, the limit cycle oscillation (LCO) onset velocity and the post-critical response peak of torsional motion are insensitive to the store mass center position. But the post-critical response of store pitch is violent if the store mass center is not under the elastic center. In the case of pylon with hard spring, the post-critical response of store pitch becomes very complex. Though the response peak of the store is small, the LCO onset velocity changes obviously with the variation of the store mass center position. The store-related kinematics will play an important role on the nonlinear responses of the system in this situation.

Modeling of airfoil aeroelastic response to gust and rain coupled loads

The aeroelastic response of an airfoil featuring plunging-pitching coupled motion in an incompressible flow field to gust and rain coupled loads is primarily investigated in this paper. The equations of airfoil coupled motion are derived by the “typical section” approach and the aeroelastic model is achieved by coupling these to 2D unsteady aerodynamics models for incompressible potential flows. The modelings of the unsteady aerodynamic and gust loads are established by the use of the Wagner’s and the Küssner’s functions, respectively. The incorporation of the rain effect is implemented via substituting the values of the slope of lift curve in the rain conditions in the aeroelastic response equations. Numerical modelings of the aeroelastic response to gusts of different velocity distributions and comparisons with the solution obtained for the rigid and elastic models featuring plunging or pitching motion alone and plunging-pitching coupled motion are provided. The pertinent results agree well with the results from other literature. The influences of gust, rain and airfoil control parameters are specially presented and discussed in detail. These results seem new and should have important reference value to the optimization of aircraft structure for the industrial aviation community.

Nonlinear Static Aeroelastic and Trim Analysis of Highly Flexible Joined-Wing Aircraft

The static aeroelastic responses and trim solutions of a high-aspect-ratio all-wing joined-wing aircraft are presented. The basics of the computational framework are the coupling of a geometrically nonlinear three-dimensional (3-D) corotational double-spar structural model with a 3-D nonplanar vortex lattice aerodynamic model. Inertia relief is exploited in the aeroelastic calculation for the first time to account for the effects of mass distribution on the static deformations of the unconstrained flying aircraft. A static structural test of the outer wing and a qualitative flight test are conducted to verify the numerical model. Numerical results of the aeroelastic deformations, lift predictions, the aerodynamic coefficients and their derivatives, as well as the trim solutions are presented and analyzed in detail and compared with rigid, linear, and nonlinear structural models. The present work provides sound insights on the aeroelastic behaviors of the flexible high-aspect-ratio joined-wing aircraft, which emphasize once more the importance of taking into account the geometric nonlinearity in the design and analysis of flexible aircraft.