NONLINEAR ASPECTS OF TRANSONIC AEROELASTICITY

Flutter analysis of airfoils in transonic flow has traditionally assumed linearity of the aerodynamic loads and moment with motion amplitude. However, the non-linear nature of the mixed flow, incorporating large amplitude shock wave motion, may significantly invalidate the lipearity assumption. In this thesis, the effect of nonlinear transonic aerodynamics on the flutter analysis is analyzed utilising a simplified linear structural model. The aerodynamic con di ti ons under which these effeds are significant are determined for specific cases using the NA CA 64AOI0 airfoil. In order to accurately determine the aerodynamic loads and moment., an un-steady fuU poten ti al code was developed. This code was joined to an algorithm which integrates the structural equations of motion in time. A flutter analysis based on the assumption of linear aerodynamics was carried out to determine the neutral stability conditions defined by a set of structural and aerodynamic param-eters. These neutral stability conditions we re then used in the structural equations of motion with nonlinear aerodynamic loads and moment. These equations were then integrated in time to determine the response of the system. If the time re-sponse was not neutrally stabie, then the structural parameter, Jl, the airfoil-to-air mass ratio was varied until the time response was neutrally stable. If the difference in the yalue of the "nonlinear " Jl to "linear " Jl was greater than 10 percent, then that case was considered to exhibit significant nonlinearities