Linear/nonlinear behavior in unsteady transonic aerodynamics
The accurate calculation of the aerodynamic forces in unsteady transonic flow requires the solution of the nonlinear flow equations. The aeroelastician, on the other hand, seeks to treat his problems (flutter, for example) by means of linear equations whenever possible. He may do this, even when the underlying flow is nonlinear, if the perturbation forces are linear over some (perhaps small) range of unsteady amplitude of motion. This paper assesses the range of parameters over which linear behavior occurs. In particular, calculations are made for an NACA 64A006 and also an MBB-A3 airfoil oscillating in pitch over a range of amplitudes, frequencies, and Mach numbers. The primary aerodynamic method used is the well known LTRAN2 code of Ballhaus and Goorjian that provides a finite difference solution to the low frequency, small disturbance, two-dimensional potential flow equation. Comparisons are made with linear subsonic theory, local linearization theory, and, for steady flow, with the full potential equation code of Bauer, Garabedian, and Korn in both its conservative and nonconservative form. © 1983 American Institute of Aeronautics and Astronautics, Inc., All rights reserved.
Dowell, EH; Bland, SR; Williams, MH
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