Feasibility of the Navier-Stokes harmonic balance method for modelling aircraft unsteady aerodynamics

Traditionally, the models of the unsteady aerodynamic loads needed for aircraft flight simulations have been estimated using the aerodynamic derivatives approach, which, using linear aerodynamic models, provides the influence of the aircraft motion rates on the aerodynamic forces and moments. With increasing aircraft maneuverability resulting in nonlinear unsteady flow regimes, however, the linearity assumption of the conventional aerodynamic derivatives approach makes the method questionable. Methods with higher reliability have been show to be achievable by using knowledge of the aircraft aerodynamic response to harmonic excitations. Prompted by the need of rapidly and accurately estimating such response, this study demonstrates the applicability of the nonlinear frequency–domain Navier–Stokes Harmonic Balance method for predicting periodic aircraft flows with low and high levels of nonlinearity. Using the NASA Common Research Model aircraft case study, it is found that the Harmonic Balance technology yields estimates of the unsteady forces differing negligibly from those of the standard time–domain Navier–Stokes method with a runtime analysis reduced by at least one order of magnitude over that of the time–domain approach