Aero-Structural Dynamics Research Articles

High-fidelity fluid-structure interaction applied to static aeroelasticity in transonic flows

Transonic flows at high Reynolds numbers can lead to high dynamic pressures and, consequently, to aerostructural deflections of aircraft structures. This study aims to develop and validate a high-fidelity static aeroelastic analysis environment that is efficient and that can be used in an industrial setting. The aerodynamics is represented by numerical solutions of the Reynolds-averaged Navier-Stokes equations with appropriate turbulence closures. The load transfer process uses finite element shape functions in order to distribute the aerodynamic loads into the structural discretization. The structural analysis employs a modal basis approach, and a wingtip deflection convergence study is performed to find an adequate modal basis size. Radial basis functions are used for the fluid mesh displacement, and the influence of the support radius is evaluated to determine the optimal values relative to the wing mean aerodynamic chord. The capability is tested using the static aeroelastic benchmarks of the High Reynolds Aerostructural Dynamics Project (HIRENASD) and NASA's Common Research Model (CRM). The static aeroelastic results demonstrate robustness and consistency for the aerodynamic coefficients, pressure distributions, and structural deflection predictions at different normalized dynamic pressure values and grid refinement levels.

A Review of Numerical and Physical Methods for Analyzing the Coupled Hydro–Aero–Structural Dynamics of Floating Wind Turbine Systems

Recently, more wind turbine systems have been installed in deep waters far from the coast. Several concepts of floating wind turbine systems (FWTS) have been developed, among which, the semi-submersible platform—due to its applicability in different water depths, good hydrodynamic performance, and facility in the installation process—constitutes the most explored technology compared to the others. However, a significant obstacle to the industrialization of this technology is the design of a cost-effective FWTS, which can be achieved by optimizing the geometry, size, and weight of the floating platform, together with the mooring system. This is only possible by selecting a method capable of accurately analyzing the FWTS-coupled hydro–aero–structural dynamics at each design stage. Accordingly, this paper provides a detailed overview of the most commonly coupled numerical and physical methods—including their basic assumptions, formulations, limitations, and costs used for analyzing the dynamics of FWTS, mainly those supported by a semi-submersible—to assist in the choice of the most suitable method at each design phase of the FWTS. Finally, this article discusses possible future research directions to address the challenges in modeling FWTS dynamics that persist to date.

Data-driven nonlinear aeroelastic models of morphing wings for control

Accurate and efficient aeroelastic models are critically important for enabling the optimization and control of highly flexible aerospace structures, which are expected to become pervasive in future transportation and energy systems. Advanced materials and morphing wing technologies are resulting in next-generation aeroelastic systems that are characterized by highly coupled and nonlinear interactions between the aerodynamic and structural dynamics. In this work, we leverage emerging data-driven modelling techniques to develop highly accurate and tractable reduced-order aeroelastic models that are valid over a wide range of operating conditions and are suitable for control. In particular, we develop two extensions to the recent dynamic mode decomposition with control (DMDc) algorithm to make it suitable for flexible aeroelastic systems: (1) we introduce a formulation to handle algebraic equations, and (2) we develop an interpolation scheme to smoothly connect several linear DMDc models developed in different operating regimes. Thus, the innovation lies in accurately modelling the nonlinearities of the coupled aerostructural dynamics over multiple operating regimes, not restricting the validity of the model to a narrow region around a linearization point. We demonstrate this approach on a high-fidelity, three-dimensional numerical model of an airborne wind energy system, although the methods are generally applicable to any highly coupled aeroelastic system or dynamical system operating over multiple operating regimes. Our proposed modelling framework results in real-time prediction of nonlinear unsteady aeroelastic responses of flexible aerospace structures, and we demonstrate the enhanced model performance for model predictive control. Thus, the proposed architecture may help enable the widespread adoption of next-generation morphing wing technologies.

A Fast Correction Method of Model Deformation Effects in Wind Tunnel Tests

The influence of model deformation needs to be corrected before the aerodynamic force data measured in the wind tunnel is applied to aircraft design. In order to obtain the aerodynamic forces on rigid model shape, this paper presents a fast correction method by establishing a mathematical modelling method connecting aerodynamic forces and wing section torsion. The aerodynamic force coefficients on rigid model shape can then be calculated quickly just by setting section torsion to zero. A 25-point simulation dataset of the High Reynolds Number Aero-Structural Dynamics (HIRENASD) model generated by Computational Fluid Dynamics (CFD) and Static Computational Aeroelasticity (CAE) approach is used to investigate the influence of section locations, basis function type, support radius, and deformation perturbation on the prediction accuracy. Finally, the present correction method is applied to predict the aerodynamic forces on the rigid shape of a NASA common research model. The results of parametric analysis and application show that the present correction method with the Wendland’s C6 function and a support radius of 1.0 can provide a reasonable prediction of aerodynamic forces on the rigid model shape.

Simulation and Modeling of Rigid Aircraft Aerodynamic Responses to Arbitrary Gust Distributions

The stresses resulting from wind gusts can exceed the limit value and may cause large-scale structural deformation or even failure. All certified airplanes should therefore withstand the increased loads from gusts of considerable intensity. A large factor of safety will make the structure heavy and less economical. Thus, the need for accurate prediction of aerodynamic gust responses is motivated by both safety and economic concerns. This article presents the efforts to simulate and model air vehicle aerodynamic responses to various gust profiles. The computational methods developed and the research outcome will play an important role in the airplane’s structural design and certification. Cobalt is used as the flow solver to simulate aerodynamic responses to wind gusts. The code has a user-defined boundary condition capability that was tested for the first time in the present study to model any gust profile (intensity, direction, and duration) on any arbitrary configuration. Gust profiles considered include sharp edge, one minus cosine, a ramp, and a 1-cosine using tabulated data consisting of gust intensity values at discrete time instants. Test cases considered are a flat plate, a two-dimensional NACA0012 airfoil, and the high Reynolds number aero-structural dynamics (HIRENASD) configuration, which resembles a typical large passenger transport aircraft. Test cases are assumed to be rigid, and only longitudinal gust profiles are considered, though the developed codes can model any gust angle. Time-accurate simulation results show the aerodynamic responses to different gust profiles including transient solutions. Simulation results show that sharp edge responses of the flat plate agree well with the Küssner approximate function, but trends of other test cases do not match because of the thin airfoil assumptions made to derive the analytical function. Reduced order aerodynamic models are then created from the convolution integral of gust amplitude and the time-accurate responses to sharp-edge gusts. Convolution models are next used to predict aerodynamic responses to arbitrary gust profiles without the need of running time-accurate simulations for every gust shape. The results show very good agreement between developed models and simulation data.

Wing aeroelasticity analysis based on an integral boundary-layer method coupled with Euler solver

An interactive boundary-layer method, which solves the unsteady flow, is developed for aeroelastic computation in the time domain. The coupled method combines the Euler solver with the integral boundary-layer solver (Euler/BL) in a “semi-inverse” manner to compute flows with the inviscid and viscous interaction. Unsteady boundary conditions on moving surfaces are taken into account by utilizing the approximate small-perturbation method without moving the computational grids. The steady and unsteady flow calculations for the LANN wing are presented. The wing tip displacement of high Reynolds number aero-structural dynamics (HIRENASD) Project is simulated under different angles of attack. The flutter-boundary predictions for the AGARD 445.6 wing are provided. The results of the interactive boundary-layer method are compared with those of the Euler method and experimental data. The study shows that viscous effects are significant for these cases and the further data analysis confirms the validity and practicability of the coupled method.

Aeroelastic Simulations of High Reynolds Number Aero Structural Dynamics Wind Tunnel Model

This article presents results of numerical simulations of the High Reynolds Number Aero Structural Dynamics wind tunnel configuration. The activities consist of the selection of relevant transonic test cases, the setup and simulation of the numerical models, and the comparison of computational and experimental results. Two steady (static coupling) and three unsteady (forced motion) test cases were selected, all in the transonic flow regime at Mach numbers up to 0.85 and Reynolds numbers up to 23 million. Good agreement between numerical and experimental data was obtained for both the steady and the unsteady test cases. It is shown that the consideration of the static elastic deformation of the wing is indispensable for both the steady and unsteady simulations. The unsteady simulations were executed in such a way that the elastic motion of the wing in a selected structural eigenmode was prescribed in a forced motion computational fluid dynamics simulation using grid deformation. This approach yields very satisfactory results in terms of the unsteady pressure distribution.

Aeroelastic predictions for steady and unsteady flow characteristics of the HIRENASD wing

In this study, we focus on static and dynamic aeroelastic analyses of the HIRENASD wing based on reference experimental data for two different flight conditions for Aeroelastic Prediction Workshop-1. The major anticipations from the HIRENASD project are to improve the knowledge about aero-structural dynamics, and to get experimental and computational data in a wide range of flight conditions. The experiments have been formerly conducted in cryogenic medium to investigate steady and unsteady aeroelastic responses in transonic regime for low and high Reynolds numbers. For current aeroelastic computations, first, a free vibration analysis is performed in Nastran using the latest structural model provided by NASA. Sequentially, the modal solution is imported from the finite element solver to Zeus software which is an Euler equations based aeroelastic solver coupled with integral boundary layer method. The aerodynamic model and fluid structure interaction parameters are constructed in Zeus. Steady and unsteady aeroelastic results are examined for the specified stations along the wing span, and interpolated for chordwise direction so as to match them with the wind tunnel test points. The designated output parameters such as steady aerodynamic lift, moment and drag coefficients, and steady and unsteady pressure distributions along the chordwise direction are compared to the experimental data and NASA's FUN3D code results which are provided in literature.

Dynamic qualification of the HIRENASD elastic wing model

Abstract The High Reynolds Number Aero-Structural Dynamics (HIRENASD) project is conducted by the Collaborative Research Center “Flow Modulation and Fluid-Structure Interaction at Airplane Wings (SFB 401)” at RWTH Aachen University. It is funded by the Deutsche Forschungsgemeinschaft (German Research Foundation, DFG) since 2004. Steady and unsteady state experiments with an elastic semispan wing model were performed under transonic and high Reynolds number conditions in the European Transonic Windtunnel (ETW) in Cologne, Germany. The main components of the complete windtunnel assembly were the wing model itself, a piezoelectric 6-components balance and a mechanical excitation mechanism able to excite the wing model at selected resonance frequencies. These components were designed, sized and assembled at the Department of Aerospace and Lightweight Structures at RWTH Aachen University. The dynamic qualification of the windtunnel assembly under wind-off condition was carried out in the department's test laboratory. Modal survey testing based on the hammer impact method was performed, as well as response decomposition analysis using enforced excitation by means of the mechanical excitation mechanism itself. Within the qualification, a test procedure enabling investigations of modal parameter changes under wind-off and wind-on conditions in a cryogenic windtunnel was also verified.