Transonic aeroelasticity analysis using state-space unsteady aerodynamic modeling

Abstract

An aeroelastic analysis is conducted on a two-degree-of-freedom airfoil in transonic flow using a generalized state-space approximation for the unsteady aerodynamics. The aerodynamic representation is validated against computational fluid dynamic solutions for angle of attack oscillations up to Mach numbers of 0.875 and at reduced frequencies up to 1.0. Despite the inherent nonlinear nature of transonic flow, it is shown that a linear finite-state model with as few as eight states can provide a good approximation to the unsteady lift and moment behavior if appropriate allowance is made for Mach number effects on the airfoil's static lift curve slope and mean aerodynamic center. It is shown how the aerodynamic representation can be coupled to the structural equations of a typical airfoil section with bending and torsional degrees of freedom. The stability of the resulting aeroelastic system is determined by eigenanalysis. This aeroelastic analysis is shown to be in excellent agreement with calculations performed using more sophisticated unsteady aerodynamic theories.