Aeroelastic Wind Tunnel Models Research Articles

Experimental error analysis of dynamic properties for a reduced-scale high-rise building model and implications on full-scale behaviour

This paper presents a method to predict the uncertainty associated with dynamic identification of a reduced-scale model of a building structure from laboratory experiments. Systematic repetitions of dynamic identification experiments and their results were expanded through Hermite Polynomial chaos. The study describes the degree of uncertainty related to structural engineering properties of the model due to laboratory errors. Uncertainties in the physical experimental system should be adequately modelled to obtain an accurate estimate of structural safety. This is crucial to reduce prediction errors of full-scale structural performance. The method works using reliability-based optimization. Applicability of the framework is illustrated using a reduced-scale model of a high-rise building, constructed for multi-hazard dynamic experiments on a shaking table and in a wind tunnel. The still-air dynamic identification of model parameters closely affects the wind tunnel results. The method accounts for system variability and experimental error propagation, enabling evaluation of structural reliability for the corresponding full-scale structure. Results reveal that the variability introduced by laboratory errors propagates onto the estimation of structural frequencies and damping, leading to non-negligible variation of full-scale structural parameters. The corresponding probability density function of some relevant-mode full-scale vibration magnitudes is discussed as a compelling example for structural safety. The study demonstrates that experimental variability must be taken into account, particularly in the case of aeroelastic wind tunnel models, because structural response measurements are affected by this uncertainty.

Design and construction of aeroelastic wind tunnel models

AbstractThe design and building of accurately scaled aeroelastic wind-tunnel models is difficult, time consuming and very costly. With the increasing usefulness of computational methods for predicting aeroelastic phenomena, few complex models have been built in recent years. New fighter aircraft projects are also becoming more and more scarce, and transport aircraft have essentially the same configuration since half a decade. This also significantly reduces the need for aeroelastic wind-tunnel models. However, there still is an interest in the results from aeroelastic testing. In some cases new and radical configurations may warrant wind-tunnel testing and in other cases complex phenomena arising in fight testing may need carefully performed experiments to resolve problems. However, there is definitely a trend towards building models and performing testing in the support of the development of computational methods.The developments in computer technology do not only improve the computational methods for aeroelasticity. Modern Computer Aided Design and Manufacturing techniques can significantly improve the quality and efficiency of the design and build process for aeroelastic models. There have also been some recent improvements in measurement techniques which have proven very useful for testing of aeroelastic wind-tunnel models. The paper will present some new design and build techniques developed for the manufacturing of a large scale wind-tunnel model of a canard delta wing fighter aircraft configuration. In the build process fiber-reinforced composites will be used, hence, challenges and possible solutions concerning the ability to produce a model with well defined material properties and fiber angles will be discussed. Further challenges arise when both measurement equipment and adjustable control surfaces should be attached inside the model using techniques that are possible to describe with computational methods. In addition, equipment, such as pressure taps, and control surface mechanics need to fit and function in a flexible structure. As a result, the above requirements will lead to necessary compromises in the design, hence, the paper will present the choices taken during the build process and for which reasons. The use of an optical positioning measurement system will also be discussed for both the validation of model properties and non-contact measurement of model deformations during wind-tunnel testing.

Design and fabrication of an aircraft static aeroelastic model based on rapid prototyping

Purpose – The purpose of this paper is to introduce a novel method for developing static aeroelastic models based on rapid prototyping for wind tunnel testing. Design/methodology/approach – A metal frame and resin covers are applied to a static aeroelastic wind tunnel model, which uses the difference of metal and resin to achieve desired stiffness distribution by the stiffness similarity principle. The metal frame is made by traditional machining, and resin covers are formed by stereolithgraphy. As demonstrated by wind tunnel testing and stiffness measurement, the novel method of design and fabrication of the static aeroelastic model based on stereolithgraphy is practical and feasible, and, compared with that of the traditional static elastic model, is prospective due to its lower costs and shorter period for its design and production, as well as avoiding additional stiffness caused by outer filler. Findings – This method for developing static aeroelastic wind tunnel model with a metal frame and resin covers is feasible, especially for aeroelastic wind tunnel models with complex external aerodynamic shape, which could be accurately constructed based on rapid prototypes in a shorter time with a much lower cost. The developed static aeroelastic aircraft model with a high aspect ratio shows its stiffness distribution in agreement with the design goals, and it is kept in a good condition through the wind tunnel testing at a Mach number ranging from 0.4 to 0.65. Research limitations/implications – The contact stiffness between the metal frame and resin covers is difficult to calculate accurately even by using finite element analysis; in addition, the manufacturing errors have some effects on the stiffness distribution of aeroelastic models, especially for small-size models. Originality/value – The design, fabrication and ground testing of aircraft static aeroelastic models presented here provide accurate stiffness and shape stimulation in a cheaper and sooner way compared with that of traditional aeroelastic models. The ground stiffness measurement uses the photogrammetry, which can provide quick, and precise, evaluation of the actual stiffness distribution of a static aeroelastic model. This study, therefore, expands the applications of rapid prototyping on wind tunnel model fabrication, especially for the practical static aeroelastic wind tunnel tests.

Design and Testing of a Blended Wing Body Aeroelastic Wind-Tunnel Model

Introduction E LASTIC wind tunnel models are frequently used to validate performanceand aeroelasticbehaviorof full size aircraft structures, for example, see Sensburg et al.,1 Schneider et al.2 and Baker et al. The model usually represents a full-size structure in an aeroelastically scaled sense. Techniques based on numerical optimization are sometimes used to achieve representativemodel behavior. For example, French and Eastep4 present an approach for matching both static and dynamic aeroelasticproperties.Once manufactured, the stiffness properties of the model are usually Ž xed, but the mass distributionmay be modiŽ ed by addingmasses at various locations. Modular elastic models, for which the stiffness andmass properties can be changed,are also being developedand are used for multipurpose investigations, for example, see Amiryants and Ishmuratov.5 Both the manufacturingand the experimental testing of aeroelastic wind-tunnel models can be very complicated due to the complexity of the models and the equipment required for aeroelastic measurements.This study focuseson an experimentalapproach that allows for short design and testing cycles using limited resources. Hence, experimental data for validation purposes can be delivered at a very early phase of a new project. The aim is to use a relatively simplemodular aeroelasticmodel in combinationwithmore sophisticated,yet easy to use, experimentalequipmentfor data acquisition. For validationof aeroelasticanalysis, access to experimentaldata in terms of both aerodynamic loads and aeroelastic deformations is normally required. Whereas load measurements are routinely performed using various types of wind-tunnel balances, the concern of deformationmeasurements is usually more involved. In the present study,an opticaltechniquebasedonmultiple-cameraphotogrammetry is used in combinationwith passive re ecting markers attached to the model. One signiŽ cant advantage with passive-type markers is that no cabling inside the model is required, hence, further simplifying the model manufacturing and testing. Experiments usingmultiple-cameraphotogrammetryandpassivemarkershavealso been conducted at NASA, as reported by Burner and Liu. The particular wind tunnel model considered in this paper is designed for low-speed aeroelastic investigations of a Blended Wing Body (BWB) transport aircraft. The BWB type of nonconventional subsonic transport concept has been the objective for several studies concerning potential beneŽ ts compared to more conventional aircraft. An overview of the BWB concept and promising results are presented by Roman et al. and Liebeck et al. One important issue with the study of the BWB concept is that tools for analysis of conventional aircraft have been developed for decades, although the developmentof the BWB provides new challenges.This implies that veriŽ cation of numerical results, by using, for example, wind-tunnelmodels, becomes very important.

Transonic aeroelastic models of highly swept hypersonic lifting surfaces

Transonic aeroelastic wind-tunnel models simulating geometric and dynamic properties of lightweight, highly swept hypersonic lifting surfaces have been designed, fabricated, and tested. The aeroelastic model designs were consistent with preliminary designs of lifting surfaces for single-stage-to-orbit vehicles. The models were tested in the NASA Langley Research Center's Transonic Dynamics Tunnel. This article summarizes the design and tests conducted for each of the two models. Wind-tunnel test results are presented showing aeroelastic instability boundaries. Aeroelastic analyses, conducted for correlation with wind-tunnel results, are also presented.

Structural modeling for optimization of low aspect ratio composite wings

minor importance in the case of some hollow wings, its inclusion is essential in the case of solid core structures, such as canards, cruise-missile components, and aeroelastic windtunnel models, for which this formulation is intended. Moreover, fuselage rigid-body DOFs must also be included. Two compromises on generality help toward the goal of low computational effort without significantly affecting the effort to include all the relevant physical effects. Realistic amounts of airfoil camber have little effect on displacements due to unsteady pressure loading, suggesting that camber can be omitted for aeroelastic problems. Similarly, rotatory inertia terms can be ignored for wings of practical thickness, as shown in the text by Librescu.4 The interest lies in a structural model incorporating the physical characteristics essential to a flutter analysis of modern low AR composite wings. The model should be sufficiently accurate to account for all important structural parameters and yet sufficiently simple so as not to be computationally intensive. Such a structural model consists of a trapezoidal plate with root and tip chords parallel to the flow and with 2k symmetrically stacked, variable thickness, generally orthotropic laminae in the laminate (Figs. 1 and 2). Mindlin shear deformability5 is included with a shear correction factor (SCF) of 1.0. The wing is attached to a rigid fuselage capable of pitch and plunge. Note that the SCF generally appears as a proportionalit y factor in the coefficient Aah [Eq. (12)]. In the present parametric study, it was chosen arbitrarily as 1.0, but is to be replaced by an appropriate value in actual design. This is the simplest model retaining the essential physical

A generalized model for assessment of vortex-induced vibrations of flexible structures

The present paper proposes a one degree of freedom (1DOF) non-linear model of self limiting cyclic wind loads for application in finite element method analyses of light structures subjected to vortex shedding excitation under lock-in conditions. Being empirical by nature, the model includes three independent parameters to be determined from response tests with representative aero-elastic wind tunnel models or prototypes. The paper discusses methods for parameter identification from response data. The paper also evaluates the proposed load model versus other 1DOF empirical vortex shedding models which have found some acceptance in wind engineering.

Circu‐Rectangular Bundled Tube Office Tower—A Case History

This paper documents the structural design and analysis as it evolved in the planning of the new Four Allen Center Tower in Houston, Texas. The 1,440,000 sq ft (133,920m2) tower consists of 50 levels above grade and two levels below grade. Aeroelastic wind tunnel models predicted that extreme dynamic oscillation of the tower may occur due to the configuration of existing tall buildings surrounding the site. Dynamic wind force resistance for the silver reflective glass structure was, provided by a four‐celled “bundled framed tube” system. The bundled tube frames are comprised of two‐story high “tree column” modules located at 15 ft (4.58 m) on centers around the building perimeter. The interior tubular cell partitions are framed by three “tree beam” diagonal truss frames quadsecting the tower's curvirectangular plan shape. The superstructure gravity and lateral loadings were transferred to the soil substratum through the medium of an 8 ft‐6 in. thick concrete foundation mat.

Design and Evaluation of Miniature Control Surface Actuation Systems for Aeroelastic Models

Miniature control surface actuation systems with wide bandpass performance have been developed for two airplane aeroelastic wind tunnel models. Analysis, design, and test results are presented for: 1) electromechanical systems for the elevator, aileron, canard, and flaperon control surfaces of a 1/30 scale B-52 model, and 2) electrohydraulic systems for the trailing edge and leading edge aileron control surfaces of a 1/17 scale semispan delta wing model. The electromechanical systems utilize d.c. torque motors with position and rate feedback to achieve a bandpass capability of 50 Hz. A rotary vane hydraulic actuator (weighing less than 3 oz) and servovalve compensated with position and load pressure feedback have demonstrated a bandpass performance of over 100 Hz.