Nonlinear Aeroelastic Modeling and Analysis of 3D Highly Flexible Wings

This paper explores a low-order modeling approach to analyze dynamic stall and bifurcation behavior in highly flexible wings, with applications in designing and controlling next-generation, highly efficient air transport. The specific focus of this paper is on lower-order unsteady aerodynamic modeling with consideration of three-dimensional effects. A low-order geometrically exact flexible beam model, known as the nonlinear beam shape (NBS) formulation is used to model the flexible wing structure; it can incorporate aerodynamic load models in the form of strip theory or the unsteady vortex lattice method (UVLM). This paper's novelty is the development of a state-space 3D aerodynamic model that allows the application of efficient numerical continuation to generate bifurcation diagrams to assess nonlinear behaviors. Initially, a sectional unsteady aerodynamic model with a dynamic stall module is applied to the flexible wing along with the unsteady lifting line theorem (ULLT) to give a cheap aeroelastic model considering 3D effects. Experimental data is used to assess the ULLT model's accuracy and evaluate the capability of the developed numerical tool to predict the nonlinear aeroelastic phenomena of a high-aspect-ratio wing. However, UVLM is believed to be better at capturing both chordwise and spanwise aerodynamic variations. Thus an effort is made to convert the UVLM into a time-continuous state-space model, and the proposed new approach is based on a frozenwake, where its potential is demonstrated through prescribed motion examples.