NASA Technical Memorandum 87708 NASA - TM - 8770819860016812 A COMPUTATIONAL TRANSONIC FLUTTER BOUNDARY TRACKING PROCEDURE

An automated flutter boundary tracking procedure is presented for the efficient calculation of transonic flutter boundaries. The new procedure uses aeroelastic responses to march along the boundary by taking steps in speed and Mach number, thereby reducing the number of response calculations prevlously requi red to determi ne a transoni c fl utter boundary. The tracking procedure reduces computational costs since only two response calculations are required per Mach number and provides a complete boundary in a single Job submission. Flutter boundary results are presented for a typical airfoil section oscillating with pitch and plunge degrees of freedom. These transonic flutter boundaries are in good agreement with "exact" boundaries calculated using the conventional time-marching method. The tracking procedure was also extended to include static aeroelastic twist as a simulation of the static deformation of a wing and thus contains all of the essential features that are required to apply it to practical three-dlmensional cases. Application of the procedure is also made to flutter boundaries as a function of structural parameters, the capability of which is useful as a design tool.