Aeroelastic Effects Research Articles

Aeroelastic characteristics of inflatable reentry vehicle in transonic and supersonic regions

As an emerging space return technology, the inflatable reentry vehicle provides a new technical solution for deep space exploration, recovery of target spacecraft, and freight transport of space products. Aimed at the serious structural failure of inflatable reentry vehicle induced by the aeroelastic effect in transonic and supersonic flows, a fluid-solid coupling approach considering the effect of the inflation gas is established. The proposed model comprehensively considers the nonlinear factors of flexible inflatable film and the feedback of structural deformation on flow field. Based on this model, the static and dynamic aeroelastic problems under transonic and supersonic conditions are carefully studied. The obtained results reveal that the depressed deformations of flexible skin hinder the flow near surface and aggravate the degree of stagnation and heat dissipation, causing the surface temperature and pressure field significantly growing compared to the case of undeformed situation. Under action of the dynamic aeroelasticity, the violent low-frequency vibration induced by the turbulent wake occurs on the vehicle, which is more serious at the transonic stage condition (about Ma 0.8) or asymmetric incoming flow. The performed research indicates that the effects of the static and dynamic aeroelasticity should be fully taken into account in the design process of inflatable reentry vehicles, giving insightful guidance for engineering practice.

Aeroelastic Effect of Corrugation for an Insect-Sized Flapping Wing

The fundamental aeroelastic effect of the corrugation of an insect-sized simple flapping wing is numerically investigated. A baseline model for a corrugated flapping wing is constructed such that the balance among the aerodynamic, elastic, and inertial forces acting on the wing matches that acting on insect wings in accordance with the measured material properties of insect wings. The thickness of the corrugated airfoil and the amplitude of corrugation are systematically varied around the baseline to modulate both the natural frequencies and mode shapes. Unsteady aeroelastic simulation based on three-dimensional Naiver–Stokes equations is conducted for the corrugated flapping wings. The numerical simulation is validated by measuring the natural frequency and mean lift of corrugated flapping wings. The results indicate that the corrugation of insect flapping wings is aeroelastically effective in providing both an appropriate passive deformation and a lightweight wing. To maximize the hovering efficiency, the optimal amplitude of corrugation is 1.7 to 2.6% of the chord length, the wing mass ratio is 0.7 to 1.5, and the natural frequency is 2.1 to 2.6 times as large as the input flapping frequency. These optimal design parameters are close to (but slightly smaller than) those of insect wings.

Flow-measurements in the wake of an oscillating sessile droplet using laser-Doppler velocity profile sensor

Abstract Although relevant in many technical applications, the removal of sessile droplets on surfaces by an (air-) flow is still hard to predict. The flow around the droplet has not been investigated in detail so far but knowledge on the flow structure is essential for the assessment of appropriate drag force correlation. Small droplets (in the range of 5–40 µl) on PMMA substrate in an air flow are investigated. Due to the small size of the droplet the laser-Doppler velocity profile sensor with frequency shift is applied to measure the flow in the wake of the oscillating, still adhering droplet. Thanks to the high spatial and temporal resolution of Laser-Doppler velocity profile sensor and its capability to measure bidirectional flows, the flow behind the droplet can be precisely analyzed. Additional hot-film measurements are used to investigate the temporal behavior of the flow. Complementary, numerical simulation is performed applying a modified VOF (Volume-of-Fluid) method. The combination of the experimental and numerical data gives new insight in the wake flow structure of sessile droplets: With increasing Reynolds number, a backflow can be detected in the wake of the droplet. A separated shear layer stemming from the upper side of the droplet leads to a vortex shedding with formation of a recirculation region in the temporal mean. In contrast to rigid hemispheres, the movement of the air-liquid interface of the droplet leads to an internal flow which is driven by the outer flow structure and vice versa. This is a hint that drag coefficients of sessile droplets cannot be simply derived by analyzing flows of rigid hemispherical structures. Additionally, droplet contour and wake flow exhibit the same characteristic oscillation frequency. The corresponding Strouhal number is almost constant at 0.03 compared to the Strouhal number of a rigid hemisphere of 0.28. Therefore, it can be assumed that an aeroelastic self-excitation effect may be present that eventually leads to droplet movement.

The influence of gap- and chord-widths for multi-box girders: Superposition of flat plate flutter derivatives and section model tests

A two dimensional model based on the superposition of Theodorsen’s flat plate theory generalized to approximate the aeroelastic effects on an arbitrary multi-box bridge girder is developed. The model is compared with wind tunnel test results of a single box girder and two triple-box girders having different gap-widths between the center box and the external boxes. Reasonable agreement between the flutter derivatives obtained from single degree of freedom harmonic forced motion tests and superposition of flat plate flutter derivatives is obtained. For vertical motion, the aerodynamic damping is correlated with the sum of chord-widths of the interconnected boxes. The aerodynamic damping during harmonic torsional motion is correlated with the distance from the elastic axis of the section to the mid-chords of the external boxes. The torsional aerodynamic damping agrees with the superposition of flat plate derivatives while the torsional aerodynamic stiffness disagrees. This means that the flat plate model overestimates the critical flutter wind speed for the present sections, but it can be used to approximate the flutter derivatives: H1, H2, H3 and A2. Empirical results are used to tune the superposed flat plate model, which is then used to approximate the critical flutter wind speed for a 2200 m single span suspension bridge featuring a light-weight triple-box girder. The wind tunnel tests indicate that the light-weight triple-box girder is aerodynamically stable up to at least 70 m/s even though the torsional frequency is lower than the vertical.

Numerical Simulation Research on Static Aeroelastic Effect of the Transonic Aileron of a High Aspect Ratio Aircraf

Numerical Simulation Research on Static Aeroelastic Effect of the Transonic Aileron of a High Aspect Ratio Aircraf

Crosswind response analysis of structures with generalized Van der Pol-type aerodynamic damping by equivalent nonlinear equation method

For lightweight and lightly damped structures such as chimneys, solar towers, tall buildings and so forth, an increased crosswind response due to vortex shedding may trigger significant aero-elastic feedback between wind and structure, leading to undesired crosswind response. This study addressed estimation of the crosswind responses of tall and slender structures, where the aero-elastic effect is considered by generalized Van der Pol-type aerodynamic damping. Firstly, the nonlinear motion equation arising from nonlinear aerodynamic damping was solved by the equivalent nonlinear equation method and an analytical solution was obtained to estimate the crosswind response. Next, the accuracy of the present solution was verified by comparison with stochastic simulated results. Finally, the present analytical solution was applied to estimate the crosswind responses of square tall buildings and verified by experimental data. It was found that the present method can predict statistics of crosswind response efficiently and with satisfactory accuracy.

Flutter of Fan Blades in the Aircraft Engine in the Three-Dimensional Subsonic Gas Flow

Aeroelasticity problems arise in the different fields of technology. The accident-free operation of the airborne machines is one of the most important factors that should be taken into account during their designing and upgrading. The solution of this problem involves the implementation of many measures to provide the system reliability on the whole, including its individual elements, in particular aircraft engine, its fan whose wide-chord blades can be exposed to the wreckage due to different reasons including the aeroelastic effects, i.e. self-excited vibrations. As a result, the origination of the aeroelastic phenomenon (flutter) in design and off-design modes should be eliminated at the stage of the design and operational development of the rotor wheel that would result in a considerable increase of the level of reliability of the aircraft engine. Based on the analysis of the available methods used for the flutter prediction we can draw a conclusion that the most promising approach to the analysis of the aeroelastic behavior of the blade ring of fan is the use of the method based on the three-dimensional model of the aerodynamics and dynamics (the method used for the solution of the coupled aeroelastic problem). By solving the coupled aeroelastic problem of the nonstationary aerodynamics and elastic vibrations of the blades we can get the amplitude –frequency blade vibration spectrum for the three-dimensional gas flow, including forced vibrations and self-excided vibrations in order to increase the reliability of the blade row of turbine machines. The developed numerical method was used for the analysis of the aeroelastic behavior of the blade ring of the fan mounted in the airborne engine for the operation mode of 3520 rmp with appropriate boundary conditions at the inlet and outlet behind the ring. The computation data confirmed the origination of self-vibrations for the given fan operation mode.

Kinematic Optimization of a Flexible Wing Undergoing Flapping and Pitching

In recent years, there has been widespread interest in the design of microair vehicles (MAVs) for flapping flight with high-aspect ratio wings due to their high efficiency and energy savings. However, the flexibility of a flapping wing causes the aeroelastic effect, which remains a subject of investigation. Generally, existing research simulates active bending and twisting of flexible wings under the assumption of neglecting flapping inertia. In this research, the kinematic optimization of a bionic wing with passive deformation in forward flight while undergoing flapping and pitching is considered. To this end, a computational aeroelasticity framework, which includes the three-dimensional unsteady vortex lattice method (UVLM) and the Newmark-β method, is constructed for flapping flight. Under the assumption of linear elastic deformation, this tool is capable of simulating attached flows over a thin wing and capturing unsteady effects of wakes. A bionic numerical wing with an aspect ratio of 6.5, chord Reynolds number of 1.9 × 105, and reduced frequency less than 0.1 is investigated in kinematic optimization. The computational aeroelasticity framework is combined with a global optimization algorithm to identify the optimal kinematics that maximize the propulsive efficiency under the minimum average lift constraint. Two types of numerical wings, rigid wing and flexible wing, are considered here to compare the influence of deformation on the aerodynamics of the flapping wing. The results show that the aeroelastic effect, which increases the flapping amplitude, yields a significant improvement in terms of propulsive efficiency. In addition, the optimization algorithm maximizes the thrust efficiency while satisfying the required lift. Moreover, the optimal kinematics of both the rigid wing and the flexible wing reach the maximum flapping angle, which indicates that a larger range of motions is needed for optimal kinetics when loosening the boundary conditions.

Investigation of Structurally and Aerodynamically Mistuned Oscillating Cascade Using Fully Coupled Method

Abstract There seems to be a lack of clear and systematic understanding of physical behavior and mechanisms of mistuned blade rows, particularly in the context of the aerodynamic mistuning versus the structural (frequency) mistuning. A high-fidelity fully coupled method is desirable to investigate the vibration characteristics of aeroelasticity problems with strong fluid–structure interaction effects, as well as blade mistuning effects. In this work, the direct nonlinear time-domain fully coupled method is adopted to investigate the dynamics mechanism of a mistuned oscillating cascade. The main objectives are two-folds, first to elucidate the basic vibration characteristics of a mistuned blade row, and second to examine the aeroelastic effects of mistuning. Three conditions of interest are considered: (a) the structural mistuning only, (b) the aerodynamic mistuning only, and (c) a combination of the two. The present results show that first a mistuned configuration tends to vibrate with the same frequency and a predominantly constant interblade phase angle. Vibration amplitudes of the blades vary significantly with a strong mode localization effect for the structural mistuning. For the concurrent structural-aerodynamic mistuning, the localization is stronger than in the standalone structural mistuning case. Second, a monotonic increase of the aeroelastic stability with the structural mistuning magnitude is observed. On the other hand, the aerodynamically mistuned cascade shows a stabilizing effect with a small amount of mistuning but exhibits a destabilizing effect with a large mistuning. Furthermore, these results indicate a quite remarkable interplay between the structural and the aerodynamic mistuning. At a condition where the tuned cascade is still stable, an aero-mistuning induced unstable behavior is observed. An introduction of a large magnitude of frequency mistuning which would be stabilizing for a tuned cascade, is instead shown to have a destabilizing effect for the present combined aero-structural mistuning case.

Tuned mass damper for self-excited vibration control: Optimization involving nonlinear aeroelastic effect

The conventional target for self-excited galloping/flutter control of a civil structure often focuses on the critical wind speed. In the present work, a nonlinear control target is introduced, i.e., to ensure that the vibration amplitude is lower than a threshold value (pre-specified according to the expected structural performance) before a target wind speed. Unlike the conventional control target, the nonlinear one can take into account the underlying large-amplitude vibrations before the critical state and/or the structural safety redundancy after the critical state. To obtain the most economical TMD parameters that enable the nonlinear target, an optimization procedure involving nonlinear aeroelastic effect is developed for galloping control based on the quasi-steady aeroelastic force model, and for flutter control based on a nonlinear unsteady model. Three numerical examples involving the galloping/flutter control of different cross-sections are analyzed to demonstrate the different results designed by the conventional and nonlinear targets. It is demonstrated that the nonlinear target and optimization procedure can lead to more economical design results than the conventional ones in the galloping/flutter control for a structure with relatively large post-critical safety redundancy, and they are more reliable than the conventional ones for a structure that may experience large-amplitude vibrations before the critical wind speed. These superiorities of the nonlinear control target and new optimization procedure suggest that they may be utilized in the TMD parameter optimization for galloping/flutter control of structures in a wide domain of engineering fields.

Study of aerodynamic and inertial forces of a dovelike flapping-wing MAV by combining experimental and numerical methods

The force-generation mechanism of a dovelike flapping-wing micro air vehicle was studied by numerical simulation and experiment. To obtain the real deformation pattern of the flapping wing, the digital image correlation technology was used to measure the dynamic deformation of the wing. The dynamic deformation data were subsequently interpolated and embedded into the CFD solver to account for the aeroelastic effects. The dynamic deformation data were further used to calculate the inertial forces by regarding the wing as a system of particles to take into account the wing flexibility. The temporal variation of the forces produced by the flapping wing was measured by a miniature load cell. The numerical results provide more flow details of the unsteady aerodynamics of the flapping wing in terms of vortex formation and evolution. The calculated results of the inertial forces are analyzed and compared with the CFD results which represent the aerodynamic forces. In addition, the total forces, i.e., the sum of the CFD result and inertial result, are compared with the experimental results, and an overall good agreement is obtained.

Gust load alleviation on an aircraft wing by trailing edge Circulation Control

This paper reports an investigation of gust load alleviation using Circulation Control for a three-dimensional wing including aerodynamic and structure interaction. The Field Velocity Method is introduced to the unsteady Reynolds averaged Navier–Stokes solutions for gust response simulations. Structural dynamic equations of motion are coupled with the unsteady Reynolds averaged Navier–Stokes solutions to consider the aeroelastic effects due to the gust response. The effects of gust load alleviation on the BAH wing using Circulation Control are tested under typical ‘one-minus-cosine’ gust profiles from certification specification defined by European Aviation Safety Agency. The results show a promising capability of Circulation Control for gust load alleviation as significant gust load alleviation effects have been achieved for both the rigid and elastic BAH wings in the test cases. For the BAH wing considering aeroelasticity, the displacement oscillations induced by gusts have been effectively suppressed by Circulation Control. The results also show that Circulation Control has the fast frequency response characteristics, where more than 50% of the total change in lift coefficient can be obtained within the non-dimensional time s =U∞tc¯=1.

Numerical Investigation of Aeroelastic Deformation Effect on the NASA Common Research Model

The risk of the aeroelastic deformation of the wings to the flight safety has become increasingly prominent for commercial transport aircraft due to the requirements for lightweight structure. In this work, Reynolds averaged Navier-Stokes (RANS) method coupled with transfinite interpolation were employed to investigate the influence of static elastic deformation of wing on aerodynamic characteristics of NASA CRM. Both bend and twist distributions were scaled in numerical simulations based on dynamic pressure, which was shown to be reasonable by the compassions between the calculations and measurements. The numerical results show premature flow separation in the middle and outboard of the wing for original configuration. Furthermore, the flow separation was supressed by the upward bending of the wing and negative twist in the leading edge, and the aerodynamic characteristics of the aircraft were improved by the aeroelastic deformation.

Dynamic instability analysis of aeroelastic systems with application to aircraft wings

In this research, a set of computational algorithms have been developed to obtain a solution for steady and unsteady aeroelastic effects with specific applications to rectangular and swept aircraft wings. The solution includes calculation for the dynamic response and prediction for the occurrence of aeroelastic instability. Two aircraft wing models, under different combinations of flight conditions, were used in testing. Good results that match with those obtained in the lab have been observed, except in certain conditions where severe external conditions, such as shocks, flow separation, or transonic flow occurred. The results were also validated with multiple computational methods. For instance, the pressure coefficient, Cp, calculated with vortex lattice was also calculated with Woodward's method and showed good match. For the unsteady flow, the calculated pressure coefficient and phase angle were compared with the measured values obtained in the lab, and the calculated and experimental results were very close. The generalized aerodynamic force function (QRS) was determined using two different schemes: a direct formula using the interpolation technique and using the downwash vectors. Both schemes produced very close results. The transfer function was calculated using direct and closed form solutions, producing identical results. The instability calculation showed very close match: for case 3A, the flutter point occurred at dynamic pressure, frequency, and flutter velocity of 20.933 Hz, 0.9 Psi, and 566 fps, respectively, compared with measured values of 20.38 Hz, 0.924 Psi, and 565.8 fps. For case 3B, the results showed flutter occurring at (16.015, 0.605, and 973.2) vs (16.09, 0.62, and 973.4) measured.

Designing of the blades of aircraft propellers by the finite element method, taking into account the strength of structure

The blades of contemporary turboprop engines have a complex spatial configuration. They can be classified as shells. Methods for the shells calculation are well known. A number of computer programs have been created on their basis. However, these programs do not take into account the peculiarities associated with the mutual influence of deformations of the blade and the aerodynamic and inertial loads acting on it. The aim of this work is to develop a method of finite element calculation of aircraft propeller blades taking into account aeroelastic effects and to create a computer program on its basis that is available to a wide range of designers and engineers. The finite element method is used in a geometrically nonlinear formulation. As the initial one, the equilibrium equation is used, which includes a complete nonlinear stiffness matrix and takes into account both conservative and non-conservative loads. The blade of one of the serial propellers was calculated. The effect of deformations on the magnitude of the aerodynamic load and, as a result, on the stresses in the design sections was found and analyzed. The proposed technique and the program compiled on its basis can be used in the design of aircraft propeller blades.

Transient aeroelasticity of structures subjected to thunderstorm outflows

Literature is rich about studies which concern the insurgence of instability of structural systems under the action of steady flows, which have led to well-consolidated methods to assess the structural safety with regard to aeroelastic phenomena induced by synoptic winds. On the other hand, there are no clear references regarding aeroelasticity induced by the effect of thunderstorm outflows, events characterised by irregular variations of the wind speed and direction in a limited duration of time, which prevent the furnishing of a long time interval for the structure and the fluid to synchronise. This paper, based under the hypothesis of applicability of the classic strip and quasi-steady theory, illustrates a mathematical model able to consider the aeroelastic effects of thunderstorm outflows into the dynamic response of slender structures, from which the methodology for synoptic winds may be found as a particular case. After defining three different levels of analysis, applications regarding the Endless Column by Constantin Brâncuși under the action of ten thunderstorm outflows are proposed, whose outcomes are critically analysed and commented.

Modeling and analysis of high aspect ratio wing considering random structural parameters

With the application of advanced composite materials in High-Aspect-Ratio wings (HARW), the randomness of structural parameters, such as elastic modulus and Poisson's ratio, is enhanced. Hence, in order to explore the whole picture of aeroelastic problems, it is of great significance to study the role of random structural parameters in aeroelastic problems. In this paper, the dynamic response of flexible HARW considering random structural parameters is analyzed. An aeroelastic model of a one-dimensional cantilevered Euler–Bernoulli beam considering aerodynamic forces acting on the wing is established based on Hamilton's principle. Adopted the idea of simplifying calculation, the effect of random structural parameters is analyzed. Then, considering the elastic modulus and torsional stiffness as continuously one-dimensional random field functions, and discretized by local method. The first and second order recursive stochastic nonlinear finite element equations of wing are derived by using perturbation method. Based on it, statistical expression of aeroelastic effects of the wing is derived. Monte Carlo method is adopted to verify the effectiveness of the method. Numerical simulations indicate that the method proposed can well mirror the statistical characteristics of aeroelastic response.

Assessment of flight dynamic and static aeroelastic behaviors for jet transport aircraft subjected to instantaneous high g-loads

PurposeThe purpose of this paper is to present a quick inspection method based on the post-flight data to examine static aeroelastic behavior for transport aircraft subjected to instantaneous high g-loads.Design/methodology/approachIn the present study, the numerical approach of static aeroelasticity and two verified cases will be presented. The non-linear unsteady aerodynamic models are established through flight data mining and the fuzzy-logic modeling of artificial intelligence techniques based on post-flight data. The first and second derivatives of flight dynamic and static aeroelastic behaviors, respectively, are then estimated by using these aerodynamic models.FindingsThe flight dynamic and static aeroelastic behaviors with instantaneous high g-load for the two transports will be analyzed and make a comparison study. The circumstance of turbulence encounter of the new twin-jet is much serious than that of four-jet transport aircraft, but the characteristic of stability and controllability for the new twin-jet is better than those of the four-jet transport aircraft; the new twin-jet transport is also shown to have very small aeroelastic effects. The static aeroelastic behaviors for the two different types can be assessed by using this method.Practical implicationsAs the present study uses the flight data stored in a quick access recorder, an intrusive structural inspection of the post-flight can be avoided. A tentative conclusion is to prove that this method can be adapted to examine the static aeroelastic effects for transport aircraft of different weights, different sizes and different service years in tracking static aeroelastic behavior of existing different types of aircraft. In future research, one can consider to have more issues of other types of aircraft with high composite structure weight.Originality/valueThis method can be used to assist airlines to monitor the variations of flight dynamic and static aeroelastic behaviors as a complementary tool for management to improve aviation safety, operation and operational efficiency.

Numerical study on the trajectory of a long-range flexible rocket with large slenderness ratio

With the requirements of the speed, maneuverability and agility, the structure with large slenderness ratio is widely employed in the design of the modern rocket. The interaction among unsteady aerodynamic load, structural elastic response, as well as flight motion will be more significant. This paper focuses on the aeroelastic effects in the trajectory simulation of a rotary rocket with a large slenderness ratio. A calculation method based on computational fluid dynamics / computational structural dynamics / computational flight mechanics (CFD/CSD/CFM) coupling system is proposed, in which an in-house CFD/CSD strong-coupled program is connected with the six-degree-of-freedom flight mechanics' equations. The CFD/CSD coupling subsystem as well as CFD/CFM coupling subsystem are validated by aeroelastic dynamic stability analysis of AGARD wing and trajectory simulation of a spinning projectile, respectively. Then, the coupling algorithm is performed on a long-range trajectory simulation of an uncontrolled rotary flexible rocket. The unsteady aerodynamic loads, structural deformation, flight motions, as well as the varying thrust direction are obtained and analyzed. Through the Monte Carlo Experiment, the landing points dispersion of the elastic rocket is also calculated and compared with the rigid case. The results show that the aeroelastic effect can decrease the range and reduce the landing accuracy of the rocket. The proposed method can provide technical support for the correction of the firing table and the design of the control system of the rocket.

A review of wind turbine drivetrain loads and load effects for fixed and floating wind turbines

AbstractDrivetrain is one of the important subsystems in the wind turbine and faults and damages in the drivetrain significantly affect the wind turbine's downtime and nonavailability. Understanding the drivetrain dynamics and load effects that results in failures has been a major research area due to challenges in the drivetrain operations and maintenance. A systematic literature review of wind turbine drivetrains is presented according to key research areas of drivetrains, such as modeling and load effects on the drivetrain. Special emphasis is given for the floating wind turbine drivetrains. A review on the state‐of‐art modeling techniques of the drivetrain is presented. Studies concerning the aeroelastic load effects on the drivetrain components especially the gearbox and the bearings are discussed. Several key aspects such as aero‐hydro‐elastic interaction load effect and platform motion excitations on the floating wind turbine drivetrain dynamics are reviewed in detail. Finally, challenges related to floating wind turbine drivetrain are also discussed.This article is categorized under: Wind Power > Science and Materials Wind Power > Systems and Infrastructure Energy Research & Innovation > Science and Materials