A review on non-linear aeroelasticity of high aspect-ratio wings

https://cyberleninka.org/article/n/1513008.pdf

Static aeroelastic analysis of very flexible wings based on non-planar vortex lattice method

Static aeroelastic analysis including geometric nonlinearities based on reduced order model

A linearization method and an engineering approach for the geometric nonlinear aeroelastic stability analysis of the very flexible aircraft with high-aspect-ratio wings are established based on the little dynamic perturbation assumption. The engineering practicability of the method is validated by a complex example. For a high-altitude long-endurance unmanned aircraft, the nonlinear static deformations under straight flight and the gust loads are calculated. At the corresponding nonlinear equilibrium state, the complete aircraft is linearized dynamically and the vibration modes are calculated considering the large deformation effects. Then the unsteady aerodynamics are calculated by the double lattice method. Finally, the aeroelastic stability of the complete aircraft is analyzed. The results are compared with the traditional linear calculation. The work shows that the geometric nonlinearity induced by the large structural deformation leads to the motion coupling of the wing chordwise bending and the torsion, which changes the mode frequencies and mode shapes. This factors change the aeroelastic coupling relationship of the flexible modes leading to the decrease of the flutter speed. The traditional linear method would give not only an imprecise flutter speed but also a possible dramatic mistake on the stability. Hence, for a high-altitude long-endurance unmanned aircraft with high-aspect-ratio wings, or a similar very flexible aircraft, the geometric nonlinear aeroelastic analysis should be a necessary job in engineering practice.

Linearization method of nonlinear aeroelastic stability for complete aircraft with high-aspect-ratio wings

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.

/pdf/geometrically-nonlinear-aeroelastic-stability-analysis-and-1mkji8cb63.pdf

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

A composite high-aspect-ratio wing of a high-altitude long-endurance (HALE) aircraft was modeled with FEM by MSC/NASTRAN, and the nonlinear static equilibrium state is calculated under design load with follower force effect, but without load redistribution. Assuming the little vibration amplitude of the wing around the static equilibrium state, the system is linearized and the natural frequencies and mode shapes of the deformed structure are obtained. Planar doublet lattice method is used to calculate unsteady aerodynamics in frequency domain ignoring the bending effect of the deflected wing. And then, the aeroelastic stability analysis of the system under a given load condition is successively carried out. Comparing with the linear results, the nonlinear displacement of the wing tip is higher. The results indicate that the critical nonlinear flutter is of the flap/chordwise bending type because of the chordwise bending having quite a large torsion component, with low critical speed and slowly growing damping, which dose not appear in the linear analysis. Furthermore, it is shown that the variation of the nonlinear flutter speed depends on the scale of the load and on the chordwise bending frequency. The research work indicates that, for the very flexible HALE aircraft, the nonlinear aeroelastic stability is very important, and should be considered in the design progress. Using present FEM software as the structure solver (e.g. MSC/NASTRAN), and the unsteady aerodynamic code, the nonlinear aeroelastic stability margin of a complex system other than a simple beam model can be determined.

/pdf/geometrical-nonlinear-aeroelastic-stability-analysis-of-a-3y7oiuyxun.pdf

Chao Yang

Papers

Geometrical nonlinear aeroelastic stability analysis of a composite high-aspect-ratio wing