Nonlinear Flutter Aspects of the Flexible HIgh-Speed Civil Transport Semispan Model

Abstract

The nonlinear aspects that lead to the flutter of the flexible semispan model of a high-speed civil transport wing configuration are analyzed. A hierarchy of spectral moments was used to determine the characteristics of the aerodynamic loading and structural strains and motions. The results show that the frequency of the bending motion of the wing varied significantly as the Mach number was increased between 0.90 and 0.97. Examination of the pressure coefficients in terms of mean value and fluctuations showed that the flow characteristics over the wing changed significantly around a Mach number of 0.97. A strong shock was identified near the trailing edge. Nonlinear analysis of the pressure fluctuations, under these conditions, showed nonlinear coupling involving lowfrequency components at pressure locations where the mean value was at a local minimum. This shows that the aerodynamic forces acting on the model had nonlinearly coupled frequency components. The presented results show how nonlinear analysis tools can be used to identify nonlinear aspects of the flutter phenomenon, which are needed in the validation of nonlinear computational methodologies.