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

The generation of reduced-order models for the evaluation of unsteady and nonlinear aerodynamic loads are investigated. The reduced-order model 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 unsteady Reynolds-averaged Navier-Stokes simulations and a grid-movement tool. Results are reported for a two-dimensional airfoil and an unmanned combat air vehicle 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 then described. The focus of the paper next shifts to assess the validity of studied reduced-order models with respect to new maneuvers. This is accomplished by comparison of the model output with time-accurate computational fluid dynamics simulations. Results presented demonstrate the feasibility of the approach for modeling unsteady aerodynamic loads and response-type computational fluid dynamics calculations.