F-16 Limit-Cycle Oscillation Analysis Using Nonlinear Damping

Abstract

A well-known F-16 external store configuration was studied using a time-domain computational aeroelasticity code. The code used a medium-fidelity Euler flow solver coupled with a linear modal representation of the structure. A key feature of the code was that it allowed the user to specify nonlinear damping profiles. Four damping profiles were investigated to determine their effects on the efficacy of this approach for predicting aeroelastic limit-cycle oscillations. Damping was specified as a function of the oscillation response, and the solution results were compared to flight test responses as a function of Mach number. Realistic limit-cycle oscillation behaviors were obtained for three of the damping profiles investigated. The oscillation amplitude trends from the analysis compared favorably to the flight tests across a wide range of sub- and transonic Mach numbers. The development of the responses from initial excitation to fully developed limit-cycle oscillations varied appropriately for the different flight conditions examined. It was observed that small variations in the damping profiles for oscillation responses below appreciably altered the predicted limit-cycle oscillation amplitude. Variations in the damping profiles for oscillation responses above were seen to alter the simulation time required to reach fully developed limit-cycle oscillations, but these variations did not significantly affect the peak oscillation amplitudes.