LINEAR/NONLINEAR BEHAVIOR IN UNSTEADY TRANSONIC AERODYNAMICS.
The accurate calculation of 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 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 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 airfoil oscillating in pitch over a range of amplitudes, frequencies, and Mach numbers. Comparisons are made with linear subsonic theory, local linearization, and, for steady flow, with a full potential equation code.