L. Maestrello
NASA Langley Res. Ctr., Mail Stop 463, Hampton, VA 23681-0001
Measurements are made of the response and acoustic radiation of a panel structure mounted in a wind tunnel and forced by a subsonic turbulent boundary layer and pure-tone sound. Measurements are made at accelerated speed because the resultant response exhibits a variety of behaviors different from data at constant speed. The structure exhibits broadband response with superimposed pure tone and its harmonics over the band, a nonlinear, nonstationary, and non-Gaussian process. The mechanism by which harmonics are generated becomes clear as the amplitudes of the fundamental and low-frequency band reduce with increasing level of the harmonics---a manifestation of energy transfer. Active control of the panel response using a time-invariant system recovers losses in relative stability as it regains partial reduction of the harmonics.