Alternative Aerodynamic Uncertainty Modeling Approaches for Flutter Reliability Analysis

Abstract

A newly developed Monte Carlo simulation-based computational capability for uncertain aeroelastic and aeroservoelastic systems is used to study flutter prediction statistics, accounting for aerodynamic and structural uncertainties. In the aerodynamics area an element-by-element aerodynamic influence coefficients based uncertainty scheme is introduced and is used to study the uncertainty of flutter predictions in the case of the historical AGARD 445.6 wing-test configuration at a sequence of transonic Mach numbers. Exploring the possibility that in an aerodynamic influence coefficient-based flutter predictions uncertainty is strongly linked to the Mach number zones in which corresponding aerodynamic boxes reside, the relative importance to the flutter velocity and frequency uncertainties of contribution of uncertainties associated with defined Mach number zones on the wing is ranked by using the method of global sensitivity analysis. An alternative approach to aerodynamic uncertainty modeling, focusing on rational function approximation matrix uncertainties, allows examination of the relative impact of uncertainty in aerodynamic stiffness, damping, inertia, or lag terms. The two approaches complement each other regarding the insights they provide into the nature of unsteady aerodynamic uncertainty. With the inclusion of structural uncertainties, the contributions of structural and aerodynamic variation to the uncertainties in flutter predictions for the AGARD 445.6 wing are compared and quantitatively ranked.