An Investigation on Viscous Effects in Downwash Weighting Methods for Transonic Aeroelastic Stability Analysis

The paper is concerned with downwash correction methods for aeroelastic stability analyses in the transonic regime. The effects of the formulation used in the calculation of nonlinear, unsteady reference pressures are addressed, together with the influence of the motion amplitude. A finite-difference Euler/Navier–Stokes code is used to calculate the unsteady aerodynamic loading due to dynamic angle of attack variations in three-dimensional transonic flow. The computed unsteady pressure coefficients are used as a reference state for flutter analyses using the downwash weighting method. The test case considered is the well-known AGARD wing 445.6 standard aeroelastic configuration. The configuration is subjected to rigid body pitching oscillation about the mid-chord point at the root section. Flutter boundaries are computed using either inviscid or viscous-based unsteady pressures in the downwash correction methodology. The results are compared with available experimental data and they indicate that both viscous and thickness effects play an important role on the flutter prediction capability.