Physics-Based Identification and Management of Aeroelastic Limit-Cycle Oscillations (LCO)

The Phase II effort presented in this proposal is intended to passively eliminate LCO by suppressing the triggering mechanism of the LCO through the concept of Targeted Energy Transfer (TET) between the aeroelastic modes of the system. The TET is physically realized through the utilization of a device known as a Nonlinear Energy Sink (NES), which provides nonlinear stiffness and inertial loading response to LCO excitations. During Phase II, initial analyses with tools developed during Phase I will be used to assess the Phase II test bed systems response and robustness to the addition of the NES. This will be done with a number of analytical methods including reduced order slow flow modeling to identify the triggering mechanisms, and various levels of CFD/structural solver couplings. The test bed itself is an existing transport wing model which has already been tested in NASA Langley Research Centers Transonic Dynamics Tunnel (TDT). Previous tests with this model have characterized the LCO behavior of the system; therefore there exist known flight conditions at which LCO occurs and will be directly mitigated by the passive application of the NES system to the existing aeroelastic model. BENEFIT: Because of a lack of established analytical methods and verification procedures for dealing with LCO phenomena, the aircraft design team is forced to work with design guidelines based upon historical or empirical findings.  These may be extremely onerous to conform to, and, at the same time, may not preclude LCOs for a particular structure in question. For example, MIL-A-87220, which is often very difficult to meet, establishes maximum allowable freeplay for various types of control surfaces.  These will dictate the use of expensive, close-tolerance bearings and thorough and frequent inspections and servicing during the aircrafts lifetime. Adherence to indirect military specifications of this nature would be rendered unnecessary by a combination of developments in the state-of-the-art of aircraft analysis tools and implementation of the NES. With analysis and design tools, analogous to those currently available for flutter calculations available to the engineer, better designs for both commercial and military aircraft in consideration of LCO behavior will be achieved, leading to vehicles requiring less inspection and maintenance and with expanded operating envelops free of LCO.