The paper is concerned with downwash correction methods for aeroelastic stability analyses in the transonic regime. A finite-difference 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 effects of the amplitudes of motion used in the calculation of nonlinear, unsteady reference pressures are addressed. 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 midchord point at the root section. Flutter boundaries are computed using unsteady pressures, in the downwash correction methodology, as reference conditions to compute weighting operators. The results are compared with available experimental data and they indicate that the aerodynamic interference and viscous and thickness effects play an important role on the flutter prediction capability. Nomenclature a = speed of sound b = reference length, taken as the semichord c = chord, 2b C p = pressure coefficient D = kernel function matrix F = substantial derivative operator h = displacement mode shape vector i = receiving point index Im = imaginary part of a complex number inst = index indicating instantaneous quantity j = sending point index k = reduced frequency based on the freestream flow speed k r = reduced frequency based on the speed of the sound K = kernel of the integral relation in terms of the acceleration potential fL a g = aerodynamic load vector M 1 = freestream Mach number n = panel number index nl = index indicating nonlinear quantity q = dynamic pressure Re = real part of a complex number S = lifting surface area S = integration matrix U 1 = freestream speed W = wake surface area [WT] = weighting function fwg= downwash vector f wg = nondimensional downwash vector x, h = planar position of doublet (discrete kernel function method) = angle of attack C p = pressure difference coefficient = dynamic angle of attack = nondimensional time step = coordinate in curvilinear system, aligned with the spanwise direction = coordinate in curvilinear system, normal to the lifting surface = coordinate in curvilinear system, tangent to the lifting surface boundary, in the streamwise direction = nondimensional time 1 = freestream condition
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