Computational Investigation into the Use of Response Functions for Aerodynamic-Load Modeling

The generation of reduced-order models (ROM) for the evaluation of unsteady and nonlinear aerodynamic loads are investigated. The ROM considered is an indicial theory based on the convolution of step functions with the derivative of the input signal. The step functions are directly calculated using the results of RANS simulations and a grid movement tool. Results are reported for a two dimensional airfoil and a UCAV configuration. Wind tunnel data are first used to validate the prediction of static and unsteady coefficients at both low and high angles of attack, with good agreement obtained for all cases. The generation of the aerodynamic models is described. The focus of the paper shifts to assess the validity of studied ROMs with respect to new maneuvres. This is accomplished by comparison of the model output with time-accurate CFD simulations. The results show that the ROMs can accurately model the unsteady loads in response to slow and fast pitch and plunge motions.