Aeroelastic Stability Analysis Research Articles

Aeroelastic Stability Analysis of a Wind Tunnel Wing Model Equipped with a True Scale Morphing Aileron

Aeroelastic Stability Analysis of a Wind Tunnel Wing Model Equipped with a True Scale Morphing Aileron

Erratum to: Aeroelastic stability analysis of flexible overexpanded rocket nozzle

Erratum to: Aeroelastic stability analysis of flexible overexpanded rocket nozzle

Assessment of a comprehensive aeroelastic tool for horizontal‐axis wind turbine rotor analysis

AbstractThis paper presents the development of a computational aeroelastic tool for the analysis of performance, response and stability of horizontal‐axis wind turbines. A nonlinear beam model for blades structural dynamics is coupled with a state‐space model for unsteady sectional aerodynamic loads, including dynamic stall effects. Several computational fluid dynamics structural dynamics coupling approaches are investigated to take into account rotor wake inflow influence on downwash, all based on a Boundary Element Method for the solution of incompressible, potential, attached flows. Sectional steady aerodynamic coefficients are extended to high angles of attack in order to characterize wind turbine operations in deep stall regimes. The Galerkin method is applied to the resulting aeroelastic differential system. In this context, a novel approach for the spatial integration of additional aerodynamic states, related to wake vorticity and dynamic stall, is introduced and assessed. Steady‐periodic blade responses are evaluated by a harmonic balance approach, whilst a standard eigenproblem is solved for aeroelastic stability analyses. Drawbacks and potentialities of the proposed model are investigated through numerical and experimental comparisons, with particular attention to rotor blades unsteady aerodynamic modelling issues. Copyright © 2016 John Wiley & Sons, Ltd.

Analysis of Aeroelastic Stability of Long Straight Wing with Store System

The aeroelastic equations of long straight wing with store system are developed in this paper by applying the Hamilton’s Principle. The dynamical model takes the store as an independent degree of freedom and considers the geometric nonlinearity of wing. The system dynamics is numerically simulated by using the Galerkin’s method. Results show that the critical flutter speed becomes largest when the store locates at wingtip and around 40% half chord before the elastic axis. The critical flutter speed will decrease as the wing-store joint rigidity decreases. On the other hand, it is shown that sudden change of flutter frequency might occur when the wing-store joint rigidity increases. Moreover, numerical results indicate buckling boundary is independent of store parameters. When the joint rigidity is relatively small, the system flutter occurs first. When the joint rigidity is relatively large, buckling occurs first. With the presence of geometric nonlinearity and increasing flow speed, the system behavior will evolve from limit cycle oscillation, to quasi-periodical motion and eventually to chaos.

Geometrically Nonlinear Aeroelastic Stability Analysis and Wind Tunnel Test Validation of a Very Flexible Wing

VFAs (very flexible aircraft) have begun to attract significant attention because of their good flight performances and significant application potentials; however, they also bring some challenges to researchers due to their unusual lightweight designs and large elastic deformations. A framework for the geometrically nonlinear aeroelastic stability analysis of very flexible wings is constructed in this paper to illustrate the unique aeroelastic characteristics and convenient use of these designs in engineering analysis. The nonlinear aeroelastic analysis model includes the geometrically nonlinear structure finite elements and steady and unsteady nonplanar aerodynamic computations (i.e., the nonplanar vortex lattice method and nonplanar doublet-lattice method). Fully nonlinear methods are used to analyse static aeroelastic features, and linearized structural dynamic equations are established at the structural nonlinear equilibrium state to estimate the stability of the system through the quasimode of the stressed and deformed structure. The exact flutter boundary is searched via an iterative procedure. A wind tunnel test is conducted to validate this theoretical analysis framework, and reasonable agreement is obtained. Both the analysis and test results indicate that the geometric nonlinearity of very flexible wings presents significantly different aeroelastic characteristics under different load cases with large deformations.

Aeroelastic stability analysis of a flexible over-expanded rocket nozzle using numerical coupling by the method of transpiration

The aim of this paper is to present and compare two different approaches for aeroelastic stability analysis of a flexible over-expanded rocket nozzle. The first approach is based on the aeroelastic stability models developed in a previous work, while the second uses the numerical fluid–structure coupling via the transpiration method. The aeroelastic frequencies of the nozzle obtained by various stability models are compared with those extracted from the numerical coupling by the method of transpiration. Both set of results show an overall good agreement.

Aeroelastic stability analysis of flexible overexpanded rocket nozzle

The aim of this paper is to present a new aeroelastic stability model taking into account the viscous effects for a supersonic nozzle flow in overexpanded regimes. This model is inspired by the Pekkari model which was developed initially for perfect fluid flow. The new model called the “Modified Pekkari Model” (MPM) considers a more realistic wall pressure profile for the case of a free shock separation inside the supersonic nozzle using the free interaction theory of Chapman. To reach this objective, a code for structure computation coupled with aerodynamic excitation effects is developed that allows the analysis of aeroelastic stability for the overexpanded nozzles. The main results are presented in a comparative manner using existing models (Pekkari model and its extended version) and the modified Pekkari model developed in this work.

Nonlinear aeroelastic stability analysis of hingeless helicopter rotor blades using FRF coupling and condition number

In this paper, aeroelastic stability analysis of hingeless helicopter blades in frequency domain is studied. In this regard, the nonlinear structural beam model of Hodges–Dowell and an unsteady aerodynamic model based on Greenberg theory and using Loewy aerodynamic function are considered to construct the aeroelastic model. Then, the concept of optimum equivalent linear frequency response function (OELF) is implemented to derive the aeroelastic FRF by coupling the aerodynamic and structural FRFs. Finally, for stability analysis, the efficient and simple criterion of condition number (CN) of aeroelastic OELF is applied. The comparison of the obtained results against those in the literature shows the capability of the OELF and condition number criterion for capturing the instability boundaries of a complex, nonlinear, aeroelastic system such as helicopter blades.

Aeroelastic Stability Analysis of High Aspect Ratio Aircraft Wings

Aeroelastic Stability Analysis of High Aspect Ratio Aircraft Wings

Aeroelastic Stability of Thermal Protection System for Inflatable Aerodynamic Decelerator

A theoretical aeroelastic stability analysis has been performed on the flexible thermal protection system for an inflatable aerodynamic decelerator. Structural models consist of one or more truncated conical shells of the Donnell type, which may be elastically supported along the middle surface. The aerodynamic model is first-order piston theory. The Lagrangian of the system is formulated in terms of the generalized coordinates for all shell displacements, and the Rayleigh–Ritz method is used to derive the equations of motion. The aeroelastic stability boundaries and mode shapes are found by calculating the eigenvalues and eigenvectors of a large coefficient matrix. When the thermal protection system is approximated as a single conical shell, circumferentially asymmetric coalescence flutter between the second and third axial modes is observed. When many circumferential elastic supports are included, the shell flutters symmetrically in zero circumferential waves, with the first, second, and third axial modes being the most critical. In this case, the flutter boundary, flutter mechanism, and critical modes may change significantly with the addition of structural damping. Aeroelastic models that consider the thermal protection system as multiple interacting shells tend to flutter asymmetrically at high dynamic pressures relative to the single shell models, with higher axial modes being more critical. It is also found that tension applied at the shell edges, orthotropicity, and elastic support stiffness are important parameters that can dramatically affect the shell’s flutter behavior.

Aeroelastic stability analysis considering a continuous flight envelope

This paper presents a new methodology to analyze aeroelastic stability in a continuous range of flight envelope with varying parameter of velocity and altitude. The focus of the paper is to demonstrate that linear matrix inequalities can be used to evaluate the aeroelastic stability in a region of flight envelope instead of a single point, like classical methods. The proposed methodology can also be used to study if a system remains stable during an arbitrary motion from one point to another in the flight envelope, i.e., when the problem becomes time-variant. The main idea is to represent the system as a polytopic differential inclusion system using rational function approximation to write the model in time domain. The theory is outlined and simulations are carried out on the benchmark AGARD 445.6 wing to demonstrate the method. The classical pk-method is used for comparing results and validating the approach. It is shown that this method is efficient to identify stability regions in the flight envelope.

Design and aeroelastic assessment of a forward-swept wing aircraft

Aeroelastic effects strongly influence the design of an aircraft. To be able to assess those effects early on, reliable simulation models representing the global aeroelastic properties of a new design are required. At a conceptual or a pre-design stage, an intelligent parameterization concept allows for limited changes of the configuration while the simulation models are adapted accordingly. In the DLR project Integrated Green Aircraft, the goal was to investigate the impact of technologies for the reduction of fuel consumption on the aeroelastic properties of aircraft. One main aspect was the influence of laminar wing design on divergence, flutter and dynamic loads. As the reference aircraft in the project, the concept of a forward-swept wing aircraft with rear-mounted engines has been analysed. An aeroelastic model has been built up in the project. The model design procedure is based on the DLR in-house tool set MONA (ModGen/NASTRAN). Focus of this design process is the generation of a parameterized structural model, representing the global dynamic properties of the elastic aircraft, but as detailed as reasonable to capture relevant local effects and to result in a feasible structural design. In the article, the aircraft design is presented. The modelling and sizing process for the structure is described. Results of the loads analysis as well as of the aeroelastic stability analyses are discussed.

Methods and advances in the study of aeroelasticity with uncertainties

Uncertainties denote the operators which describe data error, numerical error and model error in the mathematical methods. The study of aeroelasticity with uncertainty embedded in the subsystems, such as the uncertainty in the modeling of structures and aerodynamics, has been a hot topic in the last decades. In this paper, advances of the analysis and design in aeroelasticity with uncertainty are summarized in detail. According to the non-probabilistic or probabilistic uncertainty, the developments of theories, methods and experiments with application to both robust and probabilistic aeroelasticity analysis are presented, respectively. In addition, the advances in aeroelastic design considering either probabilistic or non-probabilistic uncertainties are introduced along with aeroelastic analysis. This review focuses on the robust aeroelasticity study based on the structured singular value method, namely the μ method. It covers the numerical calculation algorithm of the structured singular value, uncertainty model construction, robust aeroelastic stability analysis algorithms, uncertainty level verification, and robust flutter boundary prediction in the flight test, etc. The key results and conclusions are explored. Finally, several promising problems on aeroelasticity with uncertainty are proposed for future investigation.

Nonlinear aeroelastic stability analysis of wind turbine blade with bending–bending–twist coupling

In this study, the nonlinear aeroelastic stability of wind turbine blade with bending–bending–twist coupling has been investigated for composite thin-walled structure with pretwist angle. The aerodynamic model used here is the differential dynamic stall nonlinear ONERA model. The nonlinear aeroelastic equations are reduced to ordinary equations by Galerkin method, with the aerodynamic force decomposition by strip theory. The nonlinear resulting equations are solved by a time-marching approach, and are linearized by small perturbation about the equilibrium point. The nonlinear aeroelastic stability characteristics are investigated through eigenvalue analysis, nonlinear time domain response, and linearized time domain response.

An investigation on viscous effects in downwash weighting methods for transonic aeroelastic stability analysis

The paper is concerned with downwash correction methods for aeroelastic stability analyses in the transonic regime. The effects of the formulation used in the calculation of nonlinear, unsteady reference pressures are addressed, together with the influence of the motion amplitude. A finite-difference Euler/Navier–Stokes code is used to calculate the unsteady aerodynamic loading due to dynamic angle of attack variations in three-dimensional transonic flow. The computed unsteady pressure coefficients are used as a reference state for flutter analyses using the downwash weighting method. The test case considered is the well-known AGARD wing 445.6 standard aeroelastic configuration. The configuration is subjected to rigid body pitching oscillation about the mid-chord point at the root section. Flutter boundaries are computed using either inviscid or viscous-based unsteady pressures in the downwash correction methodology. The results are compared with available experimental data and they indicate that both viscous and thickness effects play an important role on the flutter prediction capability.

Improved Matrix Fraction Approximation of Aerodynamic Transfer Matrices

Linearized aeroelastic stability and response analyses in the state domain may require the identification of an asymptotically stable finite-state aerodynamic subsystem from available aerodynamic transfer matrices, related to structural motions and gusts. To such an aim, the paper develops an improved rational matrix approximation, combining three nonlinear least squares identification techniques with a system reduction based on a double dynamic residualization. An alternative gust formulation is also presented that, by reconstructing generalized gust forces through the use of special structural motion-like modes called gust modes, makes it possible to determine a gust response even without the usual gust-penetration model in the frequency domain. Examples are presented to demonstrate the behavior of the proposed approaches applied to sample flutter and gust/turbulence response analyses.

Solution of linear systems in Fourier-based methods for aircraft applications

Computational fluid dynamics Fourier-based methods have found increasing use for aircraft applications in the last decade. Two applications which benefit are aeroelastic stability analysis and flight dynamics for which previous work is reviewed here. The implicit solution of the methods considered in this work requires an effective preconditioner for solving the linear systems. New results are presented to understand the performance of an approach to accelerate the convergence of the linear solver. The computational performance of the resulting solver is considered for flutter and dynamic derivative calculations.

The Use of Gramian Matrices for Aeroelastic Stability Analysis

Most of the established procedures for analysis of aeroelastic flutter in the development of aircraft are based on frequency domain methods. Proposing new methodologies in this field is always a challenge, because the new methods need to be validated by many experimental procedures. With the interest for new flight control systems and nonlinear behavior of aeroelastic structures, other strategies may be necessary to complete the analysis of such systems. If the aeroelastic model can be written in time domain, using state-space formulation, for instance, then many of the tools used in stability analysis of dynamic systems may be used to help providing an insight into the aeroelastic phenomenon. In this respect, this paper presents a discussion on the use of Gramian matrices to determine conditions of aeroelastic flutter. The main goal of this work is to introduce how observability gramian matrix can be used to identify the system instability. To explain the approach, the theory is outlined and simulations are carried out on two benchmark problems. Results are compared with classical methods to validate the approach and a reduction of computational time is obtained for the second example.

Aeroelastic stability analysis of heated panel with aerodynamic loading on both surfaces

Focusing on the aeroelastic stability of thin panel structure of airframe component such as engine nozzle of high-speed flight vehicles, a nonlinear aeroelastic model for a two-dimensional heated panel exposing both surfaces to the airflow with different aerodynamic pressures is established. The von Karman large deflection plate theory and the first-order piston theory are used in the formulation of aeroelastic motion. The critical conditions for aeroelastic stability and the stability boundaries are obtained using theoretical analysis and numerical computations, respectively. The results show that the panel is more prone to become unstable when its two surfaces are subject to aerodynamic loading simultaneously; only if the sum of the aerodynamic pressures on both surfaces of the panel satisfies flutter stability condition, can the panel be likely aeroelastically stable; compared with the general panel flutter problem that only one surface is exposed to the airflows, the present condition makes the panel become aeroelastically unstable at relatively small flight aerodynamic pressure.

Flexible Launch Stability Analysis Using Steady and Unsteady Computational Fluid Dynamics

LaunchvehiclesfrequentlyexperienceareducedstabilitymarginthroughthetransonicMachnumberrange.This reduced stability margin can be caused by the aerodynamic undamping one of the lower-frequency flexible or rigidbodymodes. Analysis of the behavior of a flexible vehicle is routinely performed with quasi-steady aerodynamic line loads derived from steady rigid aerodynamics. However, a quasi-steady aeroelastic stability analysis can be unconservative at the critical Mach numbers, where experiment or unsteady computational aeroelastic analysis showareducedorevennegativeaerodynamicdamping.Amethodofenhancingthequasi-steadyaeroelasticstability analysis of a launch vehicle with unsteady aerodynamics is developed that uses unsteady computational fluid dynamics to compute the response of selected lower-frequency modes. The response is contained in a time history of the vehicle line loads. A proper orthogonal decomposition of the unsteady aerodynamic line-load response is used to reduce the scale of data volume and system identification is used to derive the aerodynamic stiffness, damping, and mass matrices. The results are compared with the damping and frequency computed from unsteady computational aeroelasticity and from a quasi-steady analysis. The results show that incorporating unsteady aerodynamics in this way brings the enhanced quasi-steady aeroelastic stability analysis into close agreement with the unsteady computational aeroelastic results.