By using a combined analytical–computational methodology, a unified modelling of aerodynamic indicial functions covering the incompressible, subsonic compressible, transonic, and supersonic flight speed regimes is presented. The procedure is carried out in conjunction with a computational fluid dynamic analysis. For a plunging–pitching airfoil, selected unsteady aerodynamic load expressions hav...

In this study, we investigate the Tchebyshev polynomials expansion method for the kernels identification of nonlinear systems. In aerodynamic systems, all the output data to an arbitrary input may be obtained by executing the Computational Fluid Dynamic (CFD) program code. This calculation process may take more than several hours or days to complete. In comparison with the indicial or impulse m...

A basic problem in flight dynamics is the mathematical formulation of the aerodynamic model for aircraft. This study is part of an ongoing effort at NASA Langley to develop a more general formulation of the aerodynamic model for aircraft that includes nonlinear unsteady aerodynamics and to develop appropriate test techniques that facilitate identification of these models. A methodology for mode...

Two 2-D aeroelastic models are presented here to determine instability boundary (flutter speed) and gust response of a typical section airfoil with degrees of freedom in pitch and plunge directions. To build these 2-D aeroelastic models, two different aerodynamic theories including Indicial Aerodynamic Theory and Vortex Lattice Method (VLM) have been employed. Also, a 3-D aeroelastic framework ...

We examine connections between A-hypergeometric di erential equations and the theory of integer programming. In the rst part, we develop a \hypergeometric sensitivity analysis" for small variations of constraint constants with creation operators and b-functions. In the second part, we study the indicial polynomial (b-function) along the hyperplane x i = 0 via a correspondence between the optima...

The goal of this work is to develop low-order models for the unsteady aerodynamic forces on a small wing in response to agile maneuvers and gusts. In a previous study, it was shown that Theodorsen’s and Wagner’s unsteady aerodynamic models agree with force data from DNS for pitching and plunging maneuvers of a 2D flat plate at Reynolds numbers between 100 and 300 as long as the reduced frequenc...

Continued studies have been undertaken to investigate and develop aerodynamic models that predict aircraft response in nonlinear unsteady flight regimes for transport configurations. The models retain conventional static and dynamic terms but replace conventional acceleration terms with indicial functions. In the Subsonic Fixed Wing Project of the NASA Fundamental Aeronautics Program and the In...

Considering the dynamic stall effects in engineering calculations is essential for correcting aerodynamic loads acting on wind turbines, both during power production and stand-still cases, impacts significantly turbine aeroelastic stability. The employed model needs to be accurate robust a wide range of airfoils angle attack. present studies are intended demonstrate performance recently impleme...

This paper proposes a method to determine the flutter derivatives of 2-dimensional streamlined cylinders by means of a modified indicial approach adapted to a Navier-Stokes solver using an Arbitrary Lagrangian Eulerian formulation. The method relies on heave or pitch motion imposed to the section according to smoothed ramp time histories and on the computational evaluation of the transient forc...