Modal Identification of Aerodynamic Models for Spanwise Lift Distribution Control

Abstract

This work presents modal identification results for the unsteady three-dimensional flow around a wing featuring multiple trailing edge flaps. The unsteady spanwise lift distribution is modeled using the unsteady vortex lattice method, which yields a linear, time-invariant, high-order state-space model. The eigensystem realization algorithm is applied for model order reduction and modal identification, providing aerodynamic mode shapes and associated eigenvalues. The wing is considered rigid, so that the dynamic mode shapes associated with the spanwise lift distribution are purely aerodynamic. It is observed that the spatial-temporal discretization of the numerical model and flap dimensions inherently limit the number of modes that can be properly identified. Open-loop simulation results demonstrate the modal behavior of the aerodynamic system. Finally, aerodynamic mode shapes for different wing planforms are also presented for comparison. By expanding the system output (lift distribution) as a truncated superposition of aerodynamic mode shapes, a low-order multiple-input and multiple-output modal representation can be obtained, suitable for controller synthesis. Ultimately, this novel approach will be applied to gust alleviation, in order to keep a desired lift distribution profile using shape control techniques.