An Investigation over CFD-Based Models for the Identification of Nonlinear Unsteady Aerodynamics Responses

An investigation is performed to assess the importance of the nonlinear effects on the dynamic behavior of a profile in a transonic flow. The analysis is done by applying a system identification approach to a computational fluid dynamics (CFD) code, considered as a black-box system. The CFD code is based on the Euler equations. Both frequency and time domain approaches are used to evaluate the nonlinear effects on the response of different airfoils. The results show that for weak shocks the aerodynamic operator describing the dynamics of the profile around a steady (transonic) flow condition is linear. For strong shocks results obtained with linear models appear to be conservative.