Nonlinear aeroelastic stability analysis and gust response of airfoil section under stall flutter oscillation

• Ano de defesa: 2021
• Autor(a) principal: Santos, Luiz Guilherme Pancini dos
• Tipo de documento: Dissertação
• Tipo de acesso: Acesso aberto
• Idioma: eng
• Instituição de defesa: Biblioteca Digitais de Teses e Dissertações da USP
• Palavras-chave em Português: atmospheric turbulence; bifurcações; bifurcations; dynamic stall; estol dinâmico; nonlinear dynamical systems; sistemas dinâmicos não-lineares; turbulência atmosférica
• Link de acesso: https://www.teses.usp.br/teses/disponiveis/18/18161/tde-08012026-155540/

A new class of flexible fixed-wing aircraft, denominated as HALE (High-Altitude-Long-Endurance) has come into the spotlight in recent years. As the desire for more flexible structures increases, so does the need to incorporate the intrinsic nonlinearities in their aeroelastic analyses. In the past, more attention has been given to the effects of structural than to aerodynamic nonlinearities. However, the very compliant wings from HALE aircraft may undergo or may need to avoid stall flutter and, therefore, depend on modeling of nolinear aerodynamic behavior such as dynamic stall. Previous prototypes have suffered structural failure under heavy turbulence, through what was believed to be gust-induced stall flutter. Since them the need for prediction of such phenomenon has become evident, but not much work has been published about it. At the preliminary stage, aeroelastic calculations routines place a limit on computational expenses and demand low-order, semi-empirical models. Therefore, in this work, a novel augmentation of the semi-empirical Beddoes-Leishman dynamic stall model to include gust loads is presented, in an effort to investigate the development of instabilities under a turbulence environment. This augmented dynamic stall model is coupled with the typical section equations of motion to yield a complete aeroelastic framework for gust-induced stall flutter analyses. The stability boundary and post-flutter behavior of a classic 2-DOF typical section representative of a HALE is investigated through bifurcation diagrams, showing limit-cycle and chaotic oscillations development in the no-gust regime. A stochastic gust response study reveals that, depending on the turbulence insensity, the probabilities of reaching aeroelastic instability can be quite high even for airspeeds well below the one for linear flutter, and make clear the requirement of modeling dynamic stall for ints accurate prediction.