Efficient Computation of Unsteady Aerodynamic Loads Using Computational-Fluid-Dynamics Linearized Methods

Abstract

In the present work, generalized aerodynamic forces concerning the time and frequency domains are analyzed. Thereby, the transonic flow regime is of main interest. For this purpose, the low-frequency structural modes of the AGARD 445.6 wing and a wing–fuselage configuration known as the fuselage cropped delta wing are used to compute the corresponding generalized aerodynamic forces with the Euler methods AER-Eu (nonlinear, time domain) and AER-SDEu (linear, frequency domain). Furthermore, a reduced-order model based on the AER-Eu solver is generated as a linear state-space model for fast computations of generalized aerodynamic forces in the discrete time domain. This is realized by recording the responses of the AER-Eu solver to a set of orthogonal step functions. The resulting time series are further processed to extract the impulse responses required for the system identification with the Eigensystem-Realization Algorithm. The transfer of the time domain results into frequency domain is achieved via the Fourier analysis of the time series of the harmonic responses and the extracted impulse responses for modal movement of the body. It is shown that the linear state-space reduced-order model based on appropriate computational-fluid-dynamics conditioning is an efficient way for the computation of generalized aerodynamic forces required in linear aeroelastic analysis.