Non-linear aeroelastic response of high aspect-ratio wings in the frequency domain

Abstract

A current trend in the aeronautic industry is to increase the wing aspect ratio to enhance aerodynamic efficiency by reducing the induced drag and thus reduce fuel consumption. Despite the associated benefits of a large aspect ratio, such as higher lift-to-drag ratios and range, commercial aircraft usually have a relatively low aspect ratio. This is partially explained by the fact that the wing becomes more flexible with increasing aspect ratio and thus more prone to large deflections, which can cause aeroelastic instability problems such as flutter. In this work, an aeroelastic study is conducted on a rectangular wing model of 20 m span and variable chord for a low subsonic speed condition to evaluate the differences between linear and non-linear static aeroelastic responses. Comparisons between linear and non-linear displacements, natural frequencies and flutter boundary are performed. An in-house non-linear aeroelastic framework was employed for this purpose. In this work, the influence of the aspect ratio and geometric non-linearity (highly deformed states) is assessed in terms of aeroelastic performance parameters: flutter speed and divergence speed. A nearly linear correlation of flutter speed difference (relative to linear analysis results) with vertical-tip displacement difference is observed. The flutter and divergence speeds vary substantially as the wing aspect ratio increases, and the divergence speeds always remain above the flutter speed. Furthermore, the flutter mechanism was observed to change as the wing chord is decreased.

On the multi-fidelity approach in surrogate-based multidisciplinary design optimisation of high-aspect-ratio wing aircraft

“…As stated before, the expectation is that increasing AR translates into higher deformations with effects on fuel consumption and flutter speed. Therefore, an FSI calculation coupling an Equivalent Beam Model (EBM) to a Panel Method (PM) is used as the low-fidelity model, using the code developed in Suleman et al [53] and Afonso et al [54]. The same EBM coupled with a RANS aerodynamic solver is used as the high-fidelity model.…”

“…The PM model includes fuselage, wing and tail components and calculates the lift and induced drag of the configuration. More detailed descriptions of these models regarding the formulation can be found in Katz and Plotkin [55] and regarding the validation in Suleman et al [53] and Afonso et al [54]. A friction drag correction is added to the calculations based on flat plate boundary layer models.…”

“…The EBM model can provide estimates of the wingbox mass, as well as the distribution of the maximum absolute value of Von-Mises stress in the beam sections along the span. The model extracts the sectional properties of the wingbox sections and translates those into an Euler-Bernoulli beam model, as described in Afonso et al [54]. The model is then used for linear structural analysis once the loading is defined.…”

“…The static FSI procedure couples the aerodynamic and structural models using an iterative procedure where the structural deformation affects the mass distribution and external geometry of the aircraft, which is then meshed and analysed in the aerodynamic solver to obtain a new load and then recalculate deformation [53,54]. The procedure is considered converged when there is no significant change in the deformation after consecutive iterations.…”

Fuzzy uncertainty analysis and reliability assessment of aeroelastic aircraft wings

“…Flutter is an undesirable phenomenon that may take place in an aeroelastic wing. One way to predict the flutter speed is via theoretical calculations based on experimentally obtained wing parameters (1)(2)(3)(4)(5) . Most of these parameters are physically uncertain due to manufacturing and operational conditions.…”