System Identification Applied to Dynamic CFD Simulation and Wind Tunnel Data

Abstract

Demanding aerodynamic modeling requirements for military and civilian aircraft have provided impetus for researchers to improve computational and experimental techniques. Model validation is a key component for these research endeavors so this study is an initial effort to extend conventional time history comparisons by comparing model parameter estimates and their standard errors using system identification methods. An aerodynamic model of an aircraft performing one-degree-of-freedom roll oscillatory motion about its body axes is developed. The model includes linear aerodynamics and deficiency function parameters characterizing an unsteady effect. For estimation of unknown parameters two techniques, harmonic analysis and two-step linear regression, were applied to roll-oscillatory wind tunnel data and to computational fluid dynamics (CFD) simulated data. The model used for this study is a highly swept wing unmanned aerial combat vehicle. Differences in response prediction, parameters estimates, and standard errors are compared and discussed.

Unsteady Aerodynamic Modeling in Roll for the NASA Generic Transport Model

“…A previous study 11 presented initial efforts to compare unsteady model parameters estimated using both CFD and dynamic wind-tunnel data. The promising results of that study have prompted the authors to extend the use of CFD simulation in this study.…”

“…An initial investigation demonstrating the potential benefits of this approach was reported in Ref. 11 …”

Investigation of Reduced-Order Modeling for Aircraft Stability and Control Prediction

“…In wind tunnels, conventional practice to obtain damping derivatives is accomplished by measuring the in-phase and out-of-phase responses from sinusoidal forced oscillations (FO) on wind-tunnel models. Initial attempts to include CFD data involved mimicking the classic FO approach with CFD tools [9][10][11]. A key advantage of the computational approach is that the limitation of very low speeds and hence Reynolds numbers due to wind-tunnel model loads is not an issue.…”

Hybrid Wing Body Model Identification Using Forced-Oscillation Water Tunnel Data

“…This approach allows for the inclusion of nonlinear behaviors and unsteady behaviors. The method takes advantage of indicial models that have been successfully applied to both transports and fighter aircraft over many years [5][6][7][8][9][10][11][12][13][14][15] . An advantage of the method is that the models retain conventional static and dynamic terms but replace conventional acceleration terms with indicial functions.…”