Ks. Breuer et al., LINEAR AND NONLINEAR EVOLUTION OF BOUNDARY-LAYER INSTABILITIES GENERATED BY ACOUSTIC-RECEPTIVITY MECHANISMS, Physics of fluids, 8(6), 1996, pp. 1415-1423
Experimental results are presented concerning the evolution of instabi
lities generated by the interaction between low-level broad-band acous
tic waves and small two-dimensional roughness elements. Streamwise per
turbation velocity spectra are measured and it is found that on the sm
ooth plate, naturally-occurring Tollmien-Schlicting (T-S) waves grow i
n a manner consistent with a resonant subharmonic wave interaction. Ho
wever, in the presence of small two-dimensional roughness elements, a
strong primary T-S mode is forced by an interaction with the backgroun
d acoustic field. This leads to a K-type of nonlinear interaction char
acterized by the generation of harmonics (up to six harmonics are obse
rved) at the expense of the subharmonic. The scaling of the T-S waves
and their harmonics with the number and amplitude of the wall roughnes
s is also considered. (C) 1996 American Institute of Physics.