Computational Static Aeroelasticity Using Nonlinear Structures and Aerodynamics Models

Abstract

High-Altitude Long-Endurance (HALE) aircraft has high aspect ratio wings to achieve the mission requirements. HALE aircraft demands high aerodynamic and structural efficiency because of lightweight and flexibility. The wings may undergo large deformations and appear the geometrically nonlinear behavior. Nonlinear structural as well as aerodynamic modeling are necessary for the aeroelastic analysis and design of HALE aircraft. The aeroelasticity of HALE aircraft has been widely studied and several nonlinear aeroelastic solvers have been developed. Van Schoor and von Flotow studied very flexible aircraft using linear finite element analysis and 2D unsteady strip theory aerodynamics. Their results indicate that unsteady aerodynamics and flexibility of the aircraft should be considered so as to correctly model the dynamic system. Patil,Hodges, and Cesnik investigated the aeroelasticity and flight dynamics of HALE aircraft. They modeled a very flexible wing as an exact intrinsic beam model with Peter’s finite-state aerodynamics. The results indicate the overall flight dynamic characteristics of the aircraft change due to wing flexibility. Drela developed an integrated design and analysis package which incorporated a nonlinear beam model with lifting-line aerodynamics. Cesnik and his co-workers have developed Nonlinear Aeroelastic Simulation Toolbox (UM/NAST) which uses a strain-based structural formulation and Peter’s finite-state aerodynamics. Several aeroealstic issues in HALE aircraft have been addressed: nonlinear aeroelastic modeling, integral wing actuation for generating maneuver loads, flutter boundary enhancement, gust load alleviation, and overall nonlinear vehicle optimization of unconventional configuration. Garcia et al. studied the the effects of transonic aerodynamics of a slender wing by coupling a Navier-Stokes solver with a nonlinear beam model. Smith et al. coupled an Euler solver with a geometrically exact beam model to investigate the effect of nonlinear aerodynamics and structures compared to various linear solutions. They concluded that linear aerodynamics theories result in larger steady state displacements and conservative flutter predictions. Palacios and Cesnik coupled a nonlinear, quasi-3D structural solver with ENS3DAE to investigate static aeroelasticity of HALE wings in compressible flow. Hallissy and Cesnik studied static and dynamic aeroelasticity of HALE wings using CFD code coupled quasi-3D, slender structural model. These solvers use the nonlinear beam models for structural descretization. This paper describes the development of structural solver based on the corotational approach using the three-node triangular shell element and the integration of existing aeroelastic solver. The static nonlinear aeroelastic responses of a high aspect ratio wing are also presented.