ASA 127th Meeting M.I.T. 1994 June 6-10

2aPA12. Nonlinear--nonstationary propagation of acoustic waves.

L. Maestrello

NASA Langley Res. Ctr., MSt 463, Hampton, VA 23681-0001

A study is made of the complex acoustic wave field emanating from a supersonic turbulent jet at constant or accelerated speeds and its interaction with a nearby flexible structure. The acoustic wave propagation from the jet and from the structure manifests period doubling, shock harmonics, and nonstationarity, all superimposed on a broadband random response field. At accelerated speeds, aperiodic (random appearing) transient multi-shock signals highly sensitive to initial conditions dominate the broadband radiation field with positive Lyapunov exponent. The shock harmonics achieve noticeable amplitude with distance with respect to the fundamental. The loading is a combination of continuous broadband stochastic-type excitation and discontinuous events from the shock impact. Transient loading plays a major role in the response dynamics of accelerated supersonic flights due to great stress/strain amplitude and high-intensity noise.