  The current work is concerned with studying processes for constructing
reduced-order models capable of performing transonic aeroelastic stability
analyses in the frequency domain based on computational fluid dynamics (CFD)
techniques. The CFD calculations are based on the Euler equations, and the code
uses a finite volume formulation for general unstructured grids. A centered
spatial discretization with added artificial dissipation is used, and an
explicit Runge-Kutta time marching method is employed. The dynamic system
considered in the present work is a NACA 0012 airfoil-based typical section in
the transonic regime. Unsteady calculations are performed for mode-by-mode and
simultaneous excitation approaches, the latter defined by orthogonal Walsh
functions. System identification techniques are employed to allow the splitting
of the aerodynamic coefficient time histories into the contribution of each
individual mode to the corresponding aerodynamic transfer functions.
Generalized unsteady aerodynamic forces are approximated by a rational transfer
function in the Laplace domain, in which nonlinear parameters are selected
through a non-gradient optimization process. Different types of interpolating
polynomials are tested and the results are compared. Results show that the
proposed procedure can reproduce literature aeroelastic analysis data with a
single unsteady CFD run.
